An extended motor network generates beta and gamma oscillatory perturbations during development

Parietal Oscillatory Dynamics Mediate Developmental Improvement in Motor Performance

Numerous recent studies have sought to determine the developmental trajectories of motor-related oscillatory responses from youth to adulthood. However, most of this work has relied on simple movements, and rarely have these studies linked developmental neural changes with maturational improvements in motor performance. In this study, we recorded magnetoencephalography during a complex finger-tapping task in a large sample of 107 healthy youth aged 9-15 years old. The relationships between region-specific neural activity, age, and performance metrics were examined using structural equation modeling. We found strong developmental effects on behavior and beta oscillatory activity during movement planning, as well as associations between planning-related beta activity and activity within the same region during the movement execution period. However, when all factors were tested, we found that only right parietal cortex beta dynamics mediated the relationship between age and performance on the task. These data suggest that strong, sustained beta activity within the right parietal cortex enhances motor performance, and that these sustained oscillations develop through childhood into early adolescence. In sum, these are the first data to link developmental trajectories in beta oscillatory dynamics with distinct motor performance metrics and implicate the right parietal cortex as a crucial hub in movement execution.

Can EEG and MEG detect signals from the human cerebellum?

The cerebellum plays a key role in the regulation of motor learning, coordination and timing, and has been implicated in sensory and cognitive processes as well. However, our current knowledge of its electrophysiological mechanisms comes primarily from direct recordings in animals, as investigations into cerebellar function in humans have instead predominantly relied on lesion, haemodynamic and metabolic imaging studies. While the latter provide fundamental insights into the contribution of the cerebellum to various cerebellar-cortical pathways mediating behaviour, they remain limited in terms of temporal and spectral resolution. In principle, this shortcoming could be overcome by monitoring the cerebellum's electrophysiological signals. Non-invasive assessment of cerebellar electrophysiology in humans, however, is hampered by the limited spatial resolution of electroencephalography (EEG) and magnetoencephalography (MEG) in subcortical structures, i.e., deep sources. Furthermore, it has been argued that the anatomical configuration of the cerebellum leads to signal cancellation in MEG and EEG. Yet, claims that MEG and EEG are unable to detect cerebellar activity have been challenged by an increasing number of studies over the last decade. Here we address this controversy and survey reports in which electrophysiological signals were successfully recorded from the human cerebellum. We argue that the detection of cerebellum activity non-invasively with MEG and EEG is indeed possible and can be enhanced with appropriate methods, in particular using connectivity analysis in source space. We provide illustrative examples of cerebellar activity detected with MEG and EEG. Furthermore, we propose practical guidelines to optimize the detection of cerebellar activity with MEG and EEG. Finally, we discuss MEG and EEG signal contamination that may lead to localizing spurious sources in the cerebellum and suggest ways of handling such artefacts. This review is to be read as a perspective review that highlights that it is indeed possible to measure cerebellum with MEG and EEG and encourages MEG and EEG researchers to do so. Its added value beyond highlighting and encouraging is that it offers useful advice for researchers aspiring to investigate the cerebellum with MEG and EEG.

The supplementary motor area syndrome and the cerebellar mutism syndrome: a pathoanatomical relationship?

PURPOSE

The supplementary motor area (SMA) syndrome affects adults after tumour resection in SMA neighbouring motor cortex. Cerebellar mutism syndrome (CMS) affects children after tumour resection in the posterior fossa. Both syndromes include disturbances in speech and motor function. The causes of the syndromes are unknown; however, surgical damage to the dentato-thalamo-cortical pathway (DTCP) has been associated with CMS. Thus, an anatomical link between the areas associated with the syndromes is possible. We discuss the syndromes and their possible relationship through the DTCP.

METHODS

We identified 61 articles (cohort studies, case reports and reviews) in MEDLINE and Embase searching for CMS, SMA syndrome or DTCP or synonyms and reviewed for evidence linking CMS and SMA.

RESULTS

We found that SMA syndrome and CMS are similar regarding (1) surgical causation; (2) symptoms including speech impairment, disturbance in motor function and facial dysfunction; (3) delayed onset; (4) the courses of the syndromes are transient; and (5) long-term sequelae are seen in both. Relevant differences include age predominance of adults in SMA syndrome versus children in CMS.

CONCLUSIONS

The similarities of the two syndromes could be traced back to their mutual connection through the DTCP and their membership to a cerebro-cerebellar circuit. The connectivity network could explain the emotional changes and speech reduction in CMS. The difference in time of post-surgical onset may be related to the anatomical distance between the surgical damage to the cerebellum and the SMA, respectively, and the effector neural loop underpinning symptoms.

Local cortical thickness predicts somatosensory gamma oscillations and sensory gating: A multimodal approach

Two largely distinct bodies of research have demonstrated age-related alterations and disease-specific aberrations in both local gamma oscillations and patterns of cortical thickness. However, seldom has the relationship between gamma activity and cortical thickness been investigated. Herein, we combine the spatiotemporal precision of magnetoencephalography (MEG) with high-resolution magnetic resonance imaging and surface-based morphometry to characterize the relationships between somatosensory gamma oscillations and the thickness of the cortical tissue generating the oscillations in 94 healthy adults (age range: 22-72). Specifically, a series of regressions were computed to assess the relationships between thickness of the primary somatosensory cortex (S1), S1 gamma response power, peak gamma frequency, and somatosensory gating of identical stimuli. Our results indicated that increased S1 thickness significantly predicted greater S1 gamma response power, reduced peak gamma frequency, and improved somatosensory gating. Furthermore, peak gamma frequency significantly and partially mediated the relationship between S1 thickness and the magnitude of the S1 gamma response. Finally, advancing age significantly predicted reduced S1 thickness and decreased gating of redundant somatosensory stimuli. Notably, this is the first study to directly link somatosensory gamma oscillations to local cortical thickness. Our results demonstrate a multi-faceted relationship between structure and function, and have important implications for understanding age- and disease-related deficits in basic sensory processing and higher-order inhibitory function.

Beta and gamma oscillations index cognitive interference effects across a distributed motor network

The planning and execution of an efficient motor plan is essential to everyday cognitive function, and relies on oscillatory neural responses in both the beta (14-30 ​Hz) and gamma (>30 ​Hz) bands. Such motor control requires not only the integration of salient information from the environment, but also the inhibition of irrelevant or distracting inputs that often manifest as forms of cognitive interference. While the effects of cognitive interference on motor neural dynamics has been an area of increasing interest recently, it remains unclear whether different subtypes of interference differentially impact these dynamics. We address this issue using magnetoencephalography and a novel adaptation of the Multi-Source Interference Task, wherein two common subtypes of cognitive interference are each presented in isolation, as well as simultaneously. We find evidence for the subtype-invariant indexing of cognitive interference across a widely distributed set of motor regions oscillating in the beta range, including the bilateral primary motor and posterior parietal cortices. Further, we find that superadditive effects of cognitive interference subtypes on behavior are paralleled by gamma oscillations in the contralateral premotor cortex, and determine that these gamma oscillations also predict the superadditive effects on behavior.

Neural oscillatory dynamics serving abstract reasoning reveal robust sex differences in typically-developing children and adolescents

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A cohort of 10–16 year-olds completed an abstract reasoning task during MEG.

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Performance on the abstract reasoning task correlated with fluid intelligence.

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The task was associated with increased cortical dynamics in frontoparietal areas.

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Youth showed sexually divergent patterns of distributed cortical activity with age.

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Specific frontoparietal activity differentially predicted aspects of task behavior.

Fluid intelligence, the ability to problem-solve in novel situations, is linked to higher-order cognitive abilities, and to academic achievement in youth. Previous research has demonstrated that fluid intelligence and the underlying neural circuitry continues to develop throughout adolescence. Neuroimaging studies have predominantly focused on identifying the spatial distribution of brain regions associated with fluid intelligence, with only a few studies examining the temporally-sensitive cortical oscillatory dynamics underlying reasoning abilities. The present study collected magnetoencephalography (MEG) during an abstract reasoning task to examine these spatiotemporal dynamics in a sample of 10-to-16 year-old youth. We found increased cortical activity across a distributed frontoparietal network. Specifically, our key results showed: (1) age was associated with increased theta activity in occipital and cerebellar regions, (2) robust sex differences were distributed across frontoparietal regions, and (3) that specific frontoparietal regions differentially predicted abstract reasoning performance among males versus females despite similar mean performance. Among males, increased theta activity mediated the relationship between age and faster reaction times; conversely, among females, decreased theta mediated the relationship between age and improved accuracy. These findings may suggest that males and females engage in distinct neurocognitive strategies across development to achieve similar behavioral outcomes during fluid reasoning tasks.

Individual differences in motor development during early childhood: An MEG study

In a previous study, we reported the first measurements of pre-movement and sensorimotor cortex activity in preschool age children (ages 3-5 years) using a customized pediatric magnetoencephalographic system. Movement-related activity in the sensorimotor cortex differed from that typically observed in adults, suggesting that maturation of cortical motor networks was still incomplete by late preschool age. Here we compare these earlier results to a group of school age children (ages 6-8 years) including seven children from the original study measured again two years later, and a group of adults (mean age 31.1 years) performing the same task. Differences in movement-related brain activity were observed both longitudinally within children in which repeated measurements were made, and cross-sectionally between preschool age children, school age children, and adults. Movement-related mu (8-12 Hz) and beta (15-30 Hz) oscillations demonstrated linear increases in amplitude and mean frequency with age. In contrast, movement-evoked gamma synchronization demonstrated a step-like transition from low (30-50 Hz) to high (70-90 Hz) narrow-band oscillations, and this occurred at different ages in different children. Notably, pre-movement activity ('readiness fields') observed in adults was absent in even the oldest children. These are the first direct observations of brain activity accompanying motor responses throughout early childhood, confirming that maturation of this activity is still incomplete by mid-childhood. In addition, individual children demonstrated markedly different developmental trajectories in movement-related brain activity, suggesting that individual differences need to be taken into account when studying motor development across age groups.

Evaluating motor cortical oscillations and age-related change in autism spectrum disorder

Autism spectrum disorder (ASD) is primarily characterized by impairments in social communication and the appearance of repetitive behaviors with restricted interests. Increasingly, evidence also points to a general deficit of motor tone and coordination in children and adults with ASD; yet the neural basis of motor functional impairment in ASD remains poorly characterized. In this study, we used magnetoencephalography (MEG) to (1) assess potential group differences between typically developing (TD) and ASD participants in motor cortical oscillatory activity observed on a simple button-press task and (2) to do so over a sufficiently broad age-range so as to capture age-dependent changes associated with development. Event-related desynchronization was evaluated in Mu (8-13 Hz) and Beta (15-30 Hz) frequency bands (Mu-ERD, Beta-ERD). In addition, post-movement Beta rebound (PMBR), and movement-related gamma (60-90 Hz) synchrony (MRGS) were also assessed in a cohort of 123 participants (63 typically developing (TD) and 59 with ASD) ranging in age from 8 to 24.9 years. We observed significant age-dependent linear trends in Beta-ERD and MRGS power with age for both TD and ASD groups; which did not differ significantly between groups. However, for PMBR, in addition to a significant effect of age, we also observed a significant reduction in PMBR power in the ASD group (p < 0.05). Post-hoc tests showed that this omnibus group difference was driven by the older cohort of children >13.2 years (p < 0.001) and this group difference was not observed when assessing PMBR activity for the younger PMBR groups (ages 8-13.2 years; p = 0.48). Moreover, for the older ASD cohort, hierarchical regression showed a significant relationship between PMBR activity and clinical scores of ASD severity (Social Responsiveness Scale (SRS T scores)), after regressing out the effect of age (p < 0.05). Our results show substantial age-dependent changes in motor cortical oscillations (Beta-ERD and MRGS) occur for both TD and ASD children and diverge only for PMBR, and most significantly for older adolescents and adults with ASD. While the functional significance of PMBR and reduced PMBR signaling remains to be fully elucidated, these results underscore the importance of considering age as a factor when assessing motor cortical oscillations and group differences in children with ASD.

Hand Motor Actions of Children With Cerebral Palsy Are Associated With Abnormal Sensorimotor Cortical Oscillations

Background. The neuroimaging literature on cerebral palsy (CP) has predominantly focused on identifying the structural aberrations (eg, fiber track integrity), with very few studies examining neural activity within the key networks that serve the production of hand movements. Objective. We aimed to start to fill this knowledge gap by using magnetoencephalographic brain imaging to quantify the temporal dynamics of the sensorimotor oscillations during a hand motor action. Methods: Children with CP (n = 12; MACS [Manual Abilities Classification System] levels I-III) and typically developing (TD) children (n = 26) performed an arrow-based version of the Eriksen flanker task where a button press was performed with either the second or third digit of the right hand depending on the arrow's direction. Results: Overall, the children with CP were less accurate and had slower reaction times compared with the TD children. These behavioral differences were closely linked with aberrant sensorimotor cortical oscillations seen in the children with CP. Compared with the TD children, the children with CP had a weaker gamma (68-82 Hz) response during motor execution and a weaker post-movement beta rebound (PMBR; 14-26 Hz) response on movement termination. Moreover, we observed a significant correlation between the amplitude of the gamma and PMBR with reaction time, with weaker gamma and PMBR responses being linked with slower reaction times. Conclusions: Overall, these results suggest that aberrations in motor-related gamma and beta cortical oscillations are associated with the impaired hand motor actions seen in children with CP.

Modulation of Motor Cortical Activities by Action Observation and Execution in Patients with Stroke: An MEG Study

Action observation therapy has recently attracted increasing attention; however, the mechanisms through which action observation and execution (AOE) modulate neural activity in stroke patients remain unclear. This study was aimed at investigating the effects of action observation and two types of AOE on motor cortical activations after stroke using magnetoencephalography. Twenty patients with stroke and 20 healthy controls were recruited for the collection of data on the beta oscillatory activity in the primary motor cortex (M1). All participants performed the conditions of resting, observation only, and video observation combined with execution (video AOE). Stroke patients performed one additional condition of affected hand observation combined with execution (affected hand AOE). The relative change index of beta oscillations was calculated, and nonparametric tests were used to examine the differences in conditions. In stroke patients, the relative change index of M1 beta oscillatory activity under the video AOE condition was significantly lower than that under the observation only and affected hand AOE conditions. Moreover, M1 cortical activity did not significantly differ under the observation only and affected hand AOE conditions. For healthy controls, the relative change index under the video AOE condition was significantly lower than that under the observation only condition. In addition, no significant differences in relative change indices were found under the observation only and video AOE conditions between the 2 groups. This study provides new insight into the neural mechanisms underlying AOE, which supports the use of observing videos of normal movements during action observation therapy in stroke rehabilitation.

Prefrontal theta modulates sensorimotor gamma networks during the reorienting of attention

The ability to execute a motor plan involves spatiotemporally precise oscillatory activity in primary motor (M1) regions, in concert with recruitment of “higher order” attentional mechanisms for orienting toward current task goals. While current evidence implicates gamma oscillatory activity in M1 as central to the execution of a movement, far less is known about top‐down attentional modulation of this response. Herein, we utilized magnetoencephalography (MEG) during a Posner attention‐reorienting task to investigate top‐down modulation of M1 gamma responses by frontal attention networks in 63 healthy adult participants. MEG data were evaluated in the time–frequency domain and significant oscillatory responses were imaged using a beamformer. Robust increases in theta activity were found in bilateral inferior frontal gyri (IFG), with significantly stronger responses evident in trials that required attentional reorienting relative to those that did not. Additionally, strong gamma oscillations (60–80 Hz) were detected in M1 during movement execution, with similar responses elicited irrespective of attentional reorienting. Whole‐brain voxel‐wise correlations between validity difference scores (i.e., attention reorienting trials—nonreorienting trials) in frontal theta activity and movement‐locked gamma oscillations revealed a robust relationship in the contralateral sensorimotor cortex, supplementary motor area, and right cerebellum, suggesting modulation of these sensorimotor network gamma responses by attentional reorienting. Importantly, the validity difference effect in this distributed motor network was predictive of overall motor function measured outside the scanner and further, based on a mediation analysis this relationship was fully mediated by the reallocation response in the right IFG. These data are the first to characterize the top‐down modulation of movement‐related gamma responses during attentional reorienting and movement execution.

Altered motor dynamics in type 1 diabetes modulate behavioral performance

Type 1 diabetes (T1D) has been linked to alterations in both brain structure and function. However, the neural basis of the most commonly reported neuropsychological deficit in T1D, psychomotor speed, remains severely understudied. To begin to address this, the current study focuses on the neural dynamics underlying motor control using magnetoencephalographic (MEG) imaging. Briefly, 40 young adults with T1D who were clear of common comorbidities (e.g., vascular disease, retinopathy, etc.) and a demographically-matched group of 40 controls without T1D completed an arrow-based flanker movement task during MEG. The resulting signals were examined in the time-frequency domain and imaged using a beamforming approach, and then voxel time series were extracted from peak responses to evaluate the dynamics. The resulting time series were statistically examined for group and conditional effects using a rigorous permutation testing approach. Our primary hypothesis was that participants with T1D would have altered beta and gamma oscillatory dynamics within the primary motor cortex during movement, and that these alterations would reflect compensatory processing to maintain adequate performance. Our results indicated that the group with T1D had a significantly stronger post-movement beta rebound (PMBR) contralateral to movement compared to controls, and a smaller neural flanker effect (i.e., difference in neural activity between conditions). In addition, a significant group-by-condition interaction was observed in the ipsilateral beta event-related desynchronization (bERD) and the ipsilateral PMBR. We also examined the relationship between oscillatory motor response amplitude and reaction time, finding a differential effect of the driving oscillatory responses on behavioral performance by group. Overall, our findings suggest compensatory activity in the motor cortices is detectable early in the disease in a relatively healthy sample of adults with T1D. Future studies are needed to examine how these subtle effects on neural activity in young, otherwise healthy patients affect outcomes in aging.

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Type 1 diabetes has been repeatedly associated with deficits in psychomotor speed.

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These deficits may reflect the impact of diabetes or common comorbidities.

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A large group of otherwise healthy patients and matched controls underwent MEG.

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Motor-related neural oscillations were imaged and statistically examined.

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Two key oscillations were aberrant in type 1 diabetics and impacted performance.

Practice modulates motor-related beta oscillations differently in adolescents and adults

KEY POINTS

Magnetoencephalography data were acquired during a leg force task in pre-/post-practice sessions in adolescents and adults. Strong peri-movement alpha and beta oscillations were mapped to the cortex. Following practice, performance improved and beta oscillations were altered. Beta oscillations decreased in the sensorimotor cortex in adolescents after practice, but increased in adults. No pre-/post-practice differences were detected for alpha oscillations.

ABSTRACT

There is considerable evidence that there are motor performance and practice differences between adolescents and adults. Behavioural studies have suggested that these motor performance differences are simply due to experience. However, the neurophysiological nexus for these motor performance differences remains unknown. The present study investigates the short-term changes (e.g. fast motor learning) in the alpha and beta event-related desynchronizations (ERDs) associated with practising an ankle plantarflexion motor action. To this end, we utilized magnetoencephalography to identify changes in the alpha and beta ERDs in healthy adolescents (n = 21; age = 14 ± 2.1 years) and middle-aged adults (n = 22; age = 36.6 ± 5 years) after practising an isometric ankle plantarflexion target-matching task. After practice, all of the participants matched more targets and matched the targets faster, and had improved accuracy, faster reaction times and faster force production. However, the motor performance of the adults exceeded what was seen in the adolescents regardless of practice. In conjunction with the behavioural results, the strength of the beta ERDs across the motor planning and execution stages was reduced after practice in the sensorimotor cortices of the adolescents, but was stronger in the adults. No pre-/post-practice changes were found in the alpha ERDs. These outcomes suggest that there are age-dependent changes in the sensorimotor cortical oscillations after practising a motor task. We suspect that these noted differences might be related to familiarity with the motor task, GABA levels and/or maturational differences in the integrity of the white matter fibre tracts that comprise the respective cortical areas.

Aberrant brain dynamics in neuroHIV: Evidence from magnetoencephalographic (MEG) imaging

Magnetoencephalography (MEG) is a noninvasive, silent, and totally passive neurophysiological imaging method with excellent temporal resolution (~1ms) and good spatial precision (~3-5mm). While MEG studies of neuroHIV remain relatively rare, the number of studies per year has sharply increased recently and this trend will likely continue into the foreseeable future. The current in-depth review focuses on the studies that have been conducted to date, which include investigations of somatosensory and visual modalities, resting-state, as well as motor control and higher-level functions such as working memory and visual attention. The review begins with an introduction to the principles and methods of MEG, and then transitions to a review of each of the empirical studies that have been conducted to date, separated by sensory modality for the basic studies and cognitive domain for the higher-level investigations. As such, this review attempts to be exhaustive in its coverage of empirical MEG studies of neuroHIV. Across studies major themes emerge including aberrant neural oscillatory activity in HIV-infected adults, both in primary sensory regions of the brain and higher-order executive regions. Many studies have also connected the amplitude of neural oscillations to behavioral and/or neuropsychological function in the study population, making a vital connection to performance and improving the veracity of the findings. One conspicuous emerging area is the use of MEG to distinguish cognitively-impaired from unimpaired HIV-infected adults, with major success reported and future studies sure to come. The review concludes with a summary of findings and suggested focus areas for future studies.

The developmental trajectory of sensorimotor cortical oscillations

Numerous studies of motor control have confirmed beta and gamma oscillations in the primary motor cortices during basic movements. These responses include a robust beta decrease that precedes and extends through movement onset, a transient gamma response that coincides with the movement, and a post-movement beta rebound (PMBR) response that occurs after movement offset. While the existence of these responses has been confirmed by many studies, very few studies have examined their developmental trajectory. In the current study, we utilized magnetoencephalography (MEG) to investigate age-related changes in sensorimotor cortical oscillations in a large cross-section of children and adolescents (n = 94; age range = 9 -15 years-old). All participants performed a stimulus detection task with their right finger and the resulting MEG data were examined using oscillatory analysis methods and imaged using a beamformer. Consistent with adult studies, these youth participants exhibited characteristic beta (16-24 Hz) decreases prior to and during movement, as well as PMBR responses following movement offset, and a transient gamma (74-84 Hz) response during movement execution. Our primary findings were that the strength of the PMBR increased with age, while the strength of the gamma synchronization decreased with chronological age. In addition, the strength of each motor-related oscillatory response was significantly correlated with the power of spontaneous activity in the same frequency range and same voxel. This was the case for all three oscillatory responses. In conclusion, we investigated motor-related oscillatory activity in the largest cohort of children and adolescents reported to date, and our results indicated that beta and gamma cortical oscillations continue to develop as children transition into adolescents, and that these responses may not be fully matured until young to middle adulthood.

Neuromagnetic Beta-Band Oscillations during Motor Imitation in Youth with Autism

Children with ASD often exhibit early difficulties with action imitation, possibly due to low-level sensory or motor impairments. Impaired cortical rhythms have been demonstrated in adults with ASD during motor imitation. While those oscillations reflect an age-dependent process, they have not been fully investigated in youth with ASD. We collected magnetoencephalography data to examine patterns of oscillatory activity in the mu (8-13 Hz) and beta frequency (15-30 Hz) range in 14 adolescents with and 14 adolescents without ASD during a fine motor imitation task. Typically developing adolescents exhibited adult-like patterns of motor signals, e.g., event-related beta and mu desynchronization (ERD) before and during the movement and a postmovement beta rebound (PMBR) after the movement. In contrast, those with ASD exhibited stronger beta and mu-ERD and reduced PMBR. Behavioral performance was similar between groups despite differences in motor cortical oscillations. Finally, we observed age-related increases in PBMR and beta-ERD in the typically developing children, but this correlation was not present in the autism group. These results suggest reduced inhibitory drive in cortical rhythms in youth with autism during intact motor imitation. Furthermore, impairments in motor brain signals in autism may not be due to delayed brain development. In the context of the excitation-inhibition imbalance perspectives of autism, we offer new insights into altered organization of neurophysiological networks.

Neurophysiological changes in the visuomotor network after practicing a motor task

Although it is well appreciated that practicing a motor task updates the associated internal model, it is still unknown how the cortical oscillations linked with the motor action change with practice. The present study investigates the short-term changes (e.g., fast motor learning) in the α- and β-event-related desynchronizations (ERD) associated with the production of a motor action. To this end, we used magnetoencephalography to identify changes in the α- and β-ERD in healthy adults after participants practiced a novel isometric ankle plantarflexion target-matching task. After practicing, the participants matched the targets faster and had improved accuracy, faster force production, and a reduced amount of variability in the force output when trying to match the target. Parallel with the behavioral results, the strength of the β-ERD across the motor-planning and execution stages was reduced after practice in the sensorimotor and occipital cortexes. No pre/postpractice changes were found in the α-ERD during motor planning or execution. Together, these outcomes suggest that fast motor learning is associated with a decrease in β-ERD power. The decreased strength likely reflects a more refined motor plan, a reduction in neural resources needed to perform the task, and/or an enhancement of the processes that are involved in the visuomotor transformations that occur before the onset of the motor action. These results may augment the development of neurologically based practice strategies and/or lead to new practice strategies that increase motor learning. NEW & NOTEWORTHY We aimed to determine the effects of practice on the movement-related cortical oscillatory activity. Following practice, we found that the performance of the ankle plantarflexion target-matching task improved and the power of the β-oscillations decreased in the sensorimotor and occipital cortexes. These novel findings capture the β-oscillatory activity changes in the sensorimotor and occipital cortexes that are coupled with behavioral changes to demonstrate the effects of motor learning.

tDCS Modulates Visual Gamma Oscillations and Basal Alpha Activity in Occipital Cortices: Evidence from MEG

Transcranial direct-current stimulation (tDCS) is now a widely used method for modulating the human brain, but the resulting physiological effects are not understood. Recent studies have combined magnetoencephalography (MEG) with simultaneous tDCS to evaluate online changes in occipital alpha and gamma oscillations, but no study to date has quantified the offline (i.e., after tDCS) alterations in these responses. Thirty-five healthy adults received active or sham anodal tDCS to the occipital cortices, and then completed a visual stimulation paradigm during MEG that is known to elicit robust gamma and alpha oscillations. The resulting MEG data were imaged and peak voxel time series were extracted to evaluate tDCS effects. We found that tDCS to the occipital increased the amplitude of local gamma oscillations, and basal alpha levels during the baseline. tDCS was also associated with network-level effects, including increased gamma oscillations in the prefrontal cortex, parietal, and other visual attention regions. Finally, although tDCS did not modulate peak gamma frequency, this variable was inversely correlated with gamma amplitude, which is consistent with a GABA-gamma link. In conclusion, tDCS alters gamma oscillations and basal alpha levels. The net offline effects on gamma activity are consistent with the view that anodal tDCS decreases local GABA.

Primary Sensorimotor Cortex Drives the Common Cortical Network for Gamma Synchronization in Voluntary Hand Movements

Background: Gamma synchronization (GS) may promote the processing between functionally related cortico-subcortical neural populations. Our aim was to identify the sources of GS and to analyze the direction of information flow in cerebral networks at the beginning of phasic movements, and during medium-strength isometric contraction of the hand.

Methods: We measured 64-channel electroencephalography in 11 healthy volunteers (age: 25 ± 8 years; four females); surface electromyography detected the movements of the dominant hand. In Task 1, subjects kept a constant medium-strength contraction of the first dorsal interosseus muscle, and performed a superimposed repetitive voluntary self-paced brisk squeeze of an object. In Task 2, brisk, and in Task 3, constant contractions were performed. Time-frequency analysis of the EEG signal was performed with the multitaper method. GS sources were identified in five frequency bands (30–49, 51–75, 76–99, 101–125, and 126–149 Hz) with beamformer inverse solution dynamic imaging of coherent sources. The direction of information flow was estimated by renormalized partial directed coherence for each frequency band. The data-driven surrogate test, and the time reversal technique were performed to identify significant connections.

Results: In all tasks, we depicted the first three common sources for the studied frequency bands that were as follows: contralateral primary sensorimotor cortex (S1M1), dorsolateral prefrontal cortex (dPFC) and supplementary motor cortex (SMA). GS was detected in narrower low- (∼30–60 Hz) and high-frequency bands (>51–60 Hz) in the contralateral thalamus and ipsilateral cerebellum in all three tasks. The contralateral posterior parietal cortex was activated only in Task 1. In every task, S1M1 had efferent information flow to the SMA and the dPFC while dPFC had no detected afferent connections to the network in the gamma range. Cortical-subcortical information flow captured by the GS was dynamically variable in the narrower frequency bands for the studied movements.

Conclusion: A distinct cortical network was identified for GS in voluntary hand movement tasks. Our study revealed that S1M1 modulated the activity of interconnected cortical areas through GS, while subcortical structures modulated the motor network dynamically, and specifically for the studied movement program.

The lifespan trajectory of neural oscillatory activity in the motor system

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The lifespan trajectory of resting and motor-related beta oscillations is unknown.

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These beta dynamics were examined in participants aged 9–75 years using MEG imaging.

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Resting beta levels and motor-related beta oscillations follow unique trajectories.

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The dynamic relationship between these two measures predicts motor performance.

Numerous studies connect beta oscillations in the motor cortices to volitional movement, and beta is known to be aberrant in multiple movement disorders. However, the dynamic interplay between these beta oscillations, motor performance, and spontaneous beta power (e.g., during rest) in the motor cortices remains unknown. This study utilized magnetoencephalography (MEG) to investigate these three parameters and their lifespan trajectory in 57 healthy participants aged 9–75 years old. Movement-related beta activity was imaged using a beamforming approach, and voxel time series data were extracted from the peak voxels in the primary motor cortices. Our results indicated that spontaneous beta power during rest followed a quadratic lifespan trajectory, while movement-related beta oscillations linearly increased with age. Follow-on analyses showed that spontaneous beta power and the beta minima during movement, together, significantly predicted task performance above and beyond the effects of age. These data are the first to show lifespan trajectories among measures of beta activity in the motor cortices, and suggest that the healthy brain compensates for age-related increases in spontaneous beta activity by increasing the strength of beta oscillations within the motor cortices which, when successful, enables normal motor performance into later life.

Attention training modulates resting-state neurophysiological abnormalities in posttraumatic stress disorder

Recent research indicates the relative benefits of computerized attention control treatment (ACT) and attention bias modification treatment (ABMT) for posttraumatic stress disorder (PTSD); however, neural changes underlying these therapeutic effects remain unknown. This study examines how these two types of attention training modulate neurological dysfunction in veterans with PTSD. A community sample of 46 combat veterans with PTSD participated in a randomized double-blinded clinical trial of ACT versus ABMT and 32 of those veterans also agreed to undergo resting-state magnetoencephalography (MEG) recordings. Twenty-four veterans completed psychological and MEG assessments at pre- and post-training to evaluate treatment effects. MEG data were imaged using an advanced Bayesian reconstruction method and examined using statistical parametric mapping. In this report, we focus on the neural correlates and the differential treatment effects observed using MEG; the results of the full clinical trial have been described elsewhere. Our results indicated that ACT modulated occipital and ABMT modulated medial temporal activity more strongly than the comparative treatment. PTSD symptoms decreased significantly from pre- to post-test. These initial neurophysiological outcome data suggest that ACT modulates visual pathways, while ABMT modulates threat-processing regions, but that both are associated with normalizing aberrant neural activity in veterans with PTSD.

Veterans with PTSD demonstrate amygdala hyperactivity while viewing threatening faces: A MEG study

Posttraumatic stress disorder (PTSD) is a major psychiatric disorder that is prevalent in combat veterans. Previous neuroimaging studies have found elevated amygdala activity in PTSD in response to threatening stimuli, but previous work has lacked the temporal specificity to study fast bottom-up fear responses involving the amygdala. Forty-four combat veterans, 28 with PTSD and 16 without, completed psychological testing and then a face-processing task during magnetoencephalography (MEG). The resulting MEG data were pre-processed, transformed into the time-frequency domain, and then imaged using a beamforming approach. We found that veterans with PTSD exhibited significantly stronger oscillatory activity from 50 to 450 ms in the left amygdala compared to veterans without PTSD while processing threatening faces. This group difference was not present while viewing neutral faces. The current study shows that amygdala hyperactivity in response to threatening cues begins quickly in PTSD, which makes theoretical sense as an adaptive bottom-up fear response.

Cerebellar Mutism Syndrome and Other Complications After Surgery in the Posterior Fossa in Adults: A Prospective Study

BACKGROUND

Cerebellar mutism syndrome (CMS) is rarely described in adults; however, data on self-assessed linguistic complications after posterior fossa surgery do not exist.

METHODS

Through a prospective single-center study, data on 59 tumor operations in the posterior fossa were collected preoperatively as well as 1 week and 1 month postoperatively. Data on self-assessed problems in 5 CMS-related domains, CMS scores, and neurology as well as surgical procedure and complications were obtained.

RESULTS

Data on CMS-related complications were obtained on 56 of the 59 operations. None was found to have CMS according to the CMS score. Within each of the 5 domains, at least 9 operations (16%) were followed by development or worsening of self-assessed CMS-related complications. Self-assessed complications were found to be most frequent after primary tumor surgeries, although they were significant only for speech and motor complications (P value = 0.01 and 0.02). Speech and language complications occurred more frequently in midline tumors compared with lateral tumors (40% vs. 7%; P = 0.004). Surgical complications were similar to other studies.

CONCLUSIONS

We propose that speech and language problems in adults undergoing surgery in the posterior fossa occur more frequently than previously assumed. Some of the self-assessed complications might reflect components of the cerebellar cognitive affective syndrome. Our findings are consistent with the fact that midline location of the tumor is one of the few known risk factors for CMS in children. Thus, the cerebellar midline seems to be a vulnerable region for speech and language complications also in adults.

The peak frequency of motor-related gamma oscillations is modulated by response competition

Movement execution generally occurs in an environment with numerous distractors, and requires the selection of a motor plan from multiple possible alternatives. However, the impact of such distractors on cortical motor function during movement remains largely unknown. Previous studies have identified two movement-related oscillatory responses that are critical to motor planning and execution, and these responses include the peri-movement beta event-related desynchronization (ERD) and the movement-related gamma synchronization (MRGS). In the current study, we investigate how visual distractors cuing alternative movements modulate the beta ERD and MRGS responses. To this end, we recorded magnetoencephalography (MEG) during an arrow-based version of the Eriksen flanker task in 42 healthy adults. All MEG data were transformed in to the time-frequency domain and the beta ERD and MRGS responses were imaged using a beamformer. Virtual sensors (voxel time series) were then extracted from the peak voxels of each response for the congruent and incongruent flanker conditions separately, and these data were examined for conditional differences during the movement. Our results indicated that participants exhibited the classic "flanker effect," as they responded significantly slower during incongruent relative to congruent trials. Our most important MEG finding was a significant increase in the peak frequency of the MRGS in the incongruent compared to the congruent condition, with no conditional effect on response amplitude. In addition, we found significantly stronger peri-movement beta ERD responses in the ipsilateral motor cortex during incongruent compared to congruent trials, but no conditional effect on frequency. These data are the first to show that the peak frequency of the MRGS response is linked to the task parameters, and varies from trial to trial in individual participants. More globally, these data suggest that beta and gamma oscillations are modulated by visual distractors causing response competition.

Children with cerebral palsy have altered oscillatory activity in the motor and visual cortices during a knee motor task

The neuroimaging literature on cerebral palsy (CP) has predominantly focused on identifying structural aberrations within the white matter (e.g., fiber track integrity), with very few studies examining neural activity within the key networks that serve the production of motor actions. The current investigation used high-density magnetoencephalography to begin to fill this knowledge gap by quantifying the temporal dynamics of the alpha and beta cortical oscillations in children with CP (age = 15.5 ± 3 years; GMFCS levels II–III) and typically developing (TD) children (age = 14.1 ± 3 years) during a goal-directed isometric target-matching task using the knee joint. Advanced beamforming methods were used to image the cortical oscillations during the movement planning and execution stages. Compared with the TD children, our results showed that the children with CP had stronger alpha and beta event-related desynchronization (ERD) within the primary motor cortices, premotor area, inferior parietal lobule, and inferior frontal gyrus during the motor planning stage. Differences in beta ERD amplitude extended through the motor execution stage within the supplementary motor area and premotor cortices, and a stronger alpha ERD was detected in the anterior cingulate. Interestingly, our results also indicated that alpha and beta oscillations were weaker in the children with CP within the occipital cortices and visual MT area during movement execution. These altered alpha and beta oscillations were accompanied by slower reaction times and substantial target matching errors in the children with CP. We also identified that the strength of the alpha and beta ERDs during the motor planning and execution stages were correlated with the motor performance. Lastly, our regression analyses suggested that the beta ERD within visual areas during motor execution primarily predicted the amount of motor errors. Overall, these data suggest that uncharacteristic alpha and beta oscillations within visuomotor cortical networks play a prominent role in the atypical motor actions exhibited by children with CP.

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Children with CP performed an isometric task with the knee joint.

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Children with CP had stronger alpha and beta ERD during motor planning.

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These ERD differences extended through the motor execution period.

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Occipital cortices and visual MT area alpha and beta ERD were weaker.

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Altered alpha and beta ERD were accompanied by impaired motor actions.

Altered sensorimotor cortical oscillations in individuals with multiple sclerosis suggests a faulty internal model

Multiple sclerosis (MS) is a demyelinating disease that results in a broad array of symptoms, including impaired motor performance. How such demyelination of fibers affects the inherent neurophysiological activity in motor circuits, however, remains largely unknown. Potentially, the movement errors associated with MS may be due to imperfections in the internal model used to make predictions of the motor output that will meet the task demands. Prior magnetoencephalographic (MEG) and electroencephalographic brain imaging experiments have established that the beta (15-30 Hz) oscillatory activity in the sensorimotor cortices is related to the control of movement. Specifically, it has been suggested that the strength of the post-movement beta rebound may indicate the certainty of the internal model. In this study, we used MEG to evaluate the neural oscillatory activity in the sensorimotor cortices of individuals with MS and healthy individuals during a goal-directed isometric knee force task. Our results showed no difference between the individuals with MS and healthy individuals in the beta activity during the planning and execution stages of movement. However, we did find that individuals with MS exhibited a weaker post-movement beta rebound in the pre/postcentral gyri relative to healthy controls. Additionally, we found that the behavioral performance of individuals with MS was aberrant, and related to the strength of the post-movement beta rebound. These results suggest that the internal model may be faulty in individuals with MS. Hum Brain Mapp 38:4009-4018, 2017. © 2017 Wiley Periodicals, Inc.

Resting-State Neurophysiological Abnormalities in Posttraumatic Stress Disorder: A Magnetoencephalography Study

Posttraumatic stress disorder (PTSD) is a debilitating psychiatric condition that is common in veterans returning from combat operations. While the symptoms of PTSD have been extensively characterized, the neural mechanisms that underlie PTSD are only vaguely understood. In this study, we examined the neurophysiology of PTSD using magnetoencephalography (MEG) in a sample of veterans with and without PTSD. Our primary hypothesis was that veterans with PTSD would exhibit aberrant activity across multiple brain networks, especially those involving medial temporal and frontal regions. To this end, we examined a total of 51 USA combat veterans with a battery of clinical interviews and tests. Thirty-one of the combat veterans met diagnostic criteria for PTSD and the remaining 20 did not have PTSD. All participants then underwent high-density MEG during an eyes-closed resting-state task, and the resulting data were analyzed using a Bayesian image reconstruction method. Our results indicated that veterans with PTSD had significantly stronger neural activity in prefrontal, sensorimotor and temporal areas compared to those without PTSD. Veterans with PTSD also exhibited significantly stronger activity in the bilateral amygdalae, parahippocampal and hippocampal regions. Conversely, healthy veterans had stronger neural activity in the bilateral occipital cortices relative to veterans with PTSD. In conclusion, these data suggest that veterans with PTSD exhibit aberrant neural activation in multiple cortical areas, as well as medial temporal structures implicated in affective processing.

The functional role of post-movement beta oscillations in motor termination

Shortly after movement termination, there is a strong increase or resynchronization of the beta rhythm (15-30 Hz) across the sensorimotor network of humans, known as the post-movement beta rebound (PMBR). This response has been associated with active inhibition of the motor network following the completion of a movement, sensory afferentation of the sensorimotor cortices, and other functions. However, studies that have directly probed the role of the PMBR in movement execution have reported mixed results, possibly due to differences in the amount of total motor output and/or movement complexity. Herein, we used magnetoencephalography during an isometric-force control task to examine whether alterations in the timing of motor termination demands modulate the PMBR, independent of differences in the motor output itself. Briefly, we manipulated the amount of time between the cue to initiate the force and the cue to terminate the force, such that participants were either forced to terminate quickly or slowly. We also performed a control experiment to test for temporal predictability effects. Our results indicated that the PMBR was stronger immediately following movement termination in the prefrontal cortices, supplementary motor area, left postcentral gyrus, paracentral lobule, and parietal cortex when participants were forced to terminate more quickly. These results were not attributable to the temporal predictability of each condition. These findings support the notion that the PMBR response at least partially serves motor inhibition, independent of the parameters within the motor output itself, and that particular nodes of the motor network may be differentially modulated by motor termination.

The cortical signature of symptom laterality in Parkinson's disease

Patients with Parkinson's disease (PD) often present with unilateral motor symptoms that eventually spread to the other side. This symptom lateralization is diagnostically important, as it serves to distinguish PD from other motor disorders with overlapping symptom profiles. Further, recent studies have shown that the side of symptom onset is important for prognosis, as there are differences in the rate of disease progression and the incidence of secondary symptoms between right- and left-dominant (RD, LD) patients. Physiologically, previous studies have shown asymmetrical decline in structure and metabolism throughout the basal ganglia, although connecting this directly to motor function has been difficult. To identify the neurophysiological basis of symptom laterality in PD, we recorded magnetoencephalography (MEG) during left- and right-hand movement paradigms in patients with PD who exhibited either RD or LD symptomatology. The beta oscillations serving these movements were then imaged using beamforming methods, and we extracted the time series of the peak voxel in the left and right primary motor cortices for each movement. In addition, each patient's symptom asymmetry was quantitated using the Unified Parkinson's Disease Rating Scale (UPDRS), which allowed the relationship between symptom asymmetry and neural asymmetry to be assessed. We found that LD patients had stronger beta suppression during movement, as well as greater post-movement beta rebound compared to patients with RD symptoms, independent of the hand that was moved. Interestingly, the asymmetry of beta activity during right-hand movement uniquely correlated with symptom asymmetry, such that the more LD the symptom profile, the more left-lateralized (i.e., contralateral to movement) the beta response; conversely, the more RD the symptom profile, the more right-lateralized (i.e., ipsilateral to movement) the beta response. This study is the first to directly probe the relationship between symptom asymmetry and the laterality of neural activity during movement in patients with PD, and suggests that LD patients have a fundamentally different and more “healthy” oscillatory pattern relative to RD patients.

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Right-dominant expression of Parkinson's has been connected to faster progression.

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Linkage between symptom asymmetry and cortical physiology remains unknown.

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Cortical motor activity was measured in patients with left/right-dominant symptoms.

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Patients with left-dominant symptoms had “healthier” pattern of motor responses.

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Laterality of cortical activity during movement was related to symptom laterality.

Neuroimaging with magnetoencephalography: A dynamic view of brain pathophysiology

Magnetoencephalography (MEG) is a noninvasive, silent, and totally passive neurophysiological imaging method with excellent temporal resolution (∼1 ms) and good spatial precision (∼3-5 mm). In a typical experiment, MEG data are acquired as healthy controls or patients with neurologic or psychiatric disorders perform a specific cognitive task, or receive sensory stimulation. The resulting data are generally analyzed using standard electrophysiological methods, coupled with advanced image reconstruction algorithms. To date, the total number of MEG instruments and associated users is significantly smaller than comparable human neuroimaging techniques, although this is likely to change in the near future with advances in the technology. Despite this small base, MEG research has made a significant impact on several areas of translational neuroscience, largely through its unique capacity to quantify the oscillatory dynamics of activated brain circuits in humans. This review focuses on the clinical areas where MEG imaging has arguably had the greatest impact in regard to the identification of aberrant neural dynamics at the regional and network level, monitoring of disease progression, determining how efficacious pharmacologic and behavioral interventions modulate neural systems, and the development of neural markers of disease. Specifically, this review covers recent advances in understanding the abnormal neural oscillatory dynamics that underlie Parkinson's disease, autism spectrum disorders, human immunodeficiency virus (HIV)-associated neurocognitive disorders, cerebral palsy, attention-deficit hyperactivity disorder, cognitive aging, and post-traumatic stress disorder. MEG imaging has had a major impact on how clinical neuroscientists understand the brain basis of these disorders, and its translational influence is rapidly expanding with new discoveries and applications emerging continuously.

Developmental Trajectory of Beta Cortical Oscillatory Activity During a Knee Motor Task

There is currently a void in the scientific literature on the cortical beta oscillatory activity that is associated with the production of leg motor actions. In addition, we have limited data on how these cortical oscillations may progressively change as a function of development. This study began to fill this vast knowledge gap by using high-density magnetoencephalography to quantify the beta cortical oscillatory activity over a cross-section of typically developing children as they performed an isometric knee target matching task. Advanced beamforming methods were used to identify the spatiotemporal changes in beta oscillatory activity during the motor planning and motor action time frames. Our results showed that a widespread beta event-related desynchronization (ERD) was present across the pre/postcentral gyri, supplementary motor area, and the parietal cortices during the motor planning stage. The strength of this beta ERD sharply diminished across this fronto-parietal network as the children initiated the isometric force needed to match the target. Rank order correlations indicated that the older children were more likely to initiate their force production sooner, took less time to match the targets, and tended to have a weaker beta ERD during the motor planning stage. Lastly, we determined that there was a relationship between the child's age and the strength of the beta ERD within the parietal cortices during isometric force production. Altogether our results suggest that there are notable maturational changes during childhood and adolescence in beta cortical oscillatory activity that are associated with the planning and execution of leg motor actions.

Is an absolute level of cortical beta suppression required for proper movement? Magnetoencephalographic evidence from healthy aging

Previous research has connected a specific pattern of beta oscillatory activity to proper motor execution, but no study to date has directly examined how resting beta levels affect motor-related beta oscillatory activity in the motor cortex. Understanding this relationship is imperative to determining the basic mechanisms of motor control, as well as the impact of pathological beta oscillations on movement execution. In the current study, we used magnetoencephalography (MEG) and a complex movement paradigm to quantify resting beta activity and movement-related beta oscillations in the context of healthy aging. We chose healthy aging as a model because preliminary evidence suggests that beta activity is elevated in older adults, and thus by examining older and younger adults we were able to naturally vary resting beta levels. To this end, healthy younger and older participants were recorded during motor performance and at rest. Using beamforming, we imaged the peri-movement beta event-related desynchronization (ERD) and extracted virtual sensors from the peak voxels, which enabled absolute and relative beta power to be assessed. Interestingly, absolute beta power during the pre-movement baseline was much stronger in older relative to younger adults, and older adults also exhibited proportionally large beta desynchronization (ERD) responses during motor planning and execution compared to younger adults. Crucially, we found a significant relationship between spontaneous (resting) beta power and beta ERD magnitude in both primary motor cortices, above and beyond the effects of age. A similar link was found between beta ERD magnitude and movement duration. These findings suggest a direct linkage between beta reduction during movement and spontaneous activity in the motor cortex, such that as spontaneous beta power increases, a greater reduction in beta activity is required to execute movement. We propose that, on an individual level, the primary motor cortices have an absolute threshold of beta power that must be reached in order to move, and that an inability to suppress beta power to this threshold results in an increase in movement duration.

Cue-related Temporal Factors Modulate Movement-related Beta Oscillatory Activity in the Human Motor Circuit

In humans, there is a strong beta (15-30 Hz) event-related desynchronization (ERD) that begins before movement, which has been tentatively linked to motor planning operations. The dynamics of this response are strongly modulated by whether a pending movement is cued and the inherent parameters of the cue. However, previous studies have focused on the information content of cues and not on parameters such as the timing of the cue relative to other events. Variations in such timing are critical, as they directly impact the amount of time that participants have to plan pending movements. In this study, participants performed finger-tapping sequences during magnetoencephalography, and we manipulated the amount of time (i.e., "long" vs. "short") between the presentation of the to-be-executed sequence and the cue to initiate the sequence. We found that the beta ERD was stronger immediately after the cue to move in the contralateral postcentral gyrus and bilateral parietal cortices during the short compared with long planning time condition. During movement execution, the beta ERD was stronger in the premotor cortex and the SMA in the short relative to long condition. Finally, peak latency in the SMA significantly correlated with RT, such that the closer the peak beta ERD was to the cue to move, the quicker the participant responded. The results of this study establish that peri-movement beta ERD activity across the cortical motor circuit is highly sensitive to cue-related temporal factors, with a direct link to motor performance.

Age-related differences in the motor planning of a lower leg target matching task

While the development and execution of upper extremity motor plans have been well explored, little is known about how individuals plan and execute rapid, goal-directed motor tasks with the lower extremities. Furthermore, the amount of time needed to integrate the proper amount of visual and proprioceptive feedback before being able to accurately execute a goal-directed movement is not well understood; especially in children. Therefore, the purpose of this study was to initially interrogate how the amount of motor planning time provided to a child before movement execution may influence the preparation and execution of a lower leg goal-directed movement. The results displayed that the amount of pre-movement motor planning time provided may influence the reaction time and accuracy of a goal directed leg movement. All subjects in the study had longer reaction times and less accurate movements when no pre-movement motor planning time was provided. In addition, the children had slower reaction times, slower movements, and less accurate movements than the adults for all the presented targets and motor planning times. These results highlight that children may require more time to successfully plan a goal directed movement with the lower extremity. This suggests that children may potentially have less robust internal models than adults for these types of motor skills.

Ipsilateral cortical motor desynchronisation is reduced in Benign Epilepsy with Centro-Temporal Spikes

OBJECTIVE

Magnetoencephalography (MEG) and a simple motor paradigm were used to study induced sensorimotor responses and their relationship to motor skills in children diagnosed with Benign Epilepsy with Centro-Temporal Spikes (BECTS).

METHODS

Twenty-one children with BECTS and 15 age-matched controls completed a finger abduction task in MEG; movement-related oscillatory responses were derived and contrasted between groups. A subset of children also completed psycho-behavioural assessments. Regression analyses explored the relationship of MEG responses to manual dexterity performance, and dependence upon clinical characteristics.

RESULTS

In children with BECTS, manual dexterity was below the population mean (p=.002) and three showed severe impairment. Our main significant finding was of reduced ipsilateral movement related beta desynchrony (MRBDi) in BECTS relative to the control group (p=.03) and predicted by epileptic seizure recency (p=.02), but not age, medication status, or duration of epilepsy. Laterality scores across the entire cohort indicated that less lateralised MRBD predicted better manual dexterity (p=.04).

CONCLUSIONS

Altered movement-related oscillatory responses in ipsilateral motor cortex were associated with motor skill deficits in children with BECTS. These changes were more marked in those with more recent seizures.

SIGNIFICANCE

These findings may reflect differences in inter-hemispheric interactions during motor control in BECTS.

Coding complexity in the human motor circuit

Cortical oscillatory dynamics are known to be critical for human movement, although their functional significance remains unclear. In particular, there is a strong beta (15-30 Hz) desynchronization that begins before movement onset and continues during movement, before rebounding after movement termination. Several studies have connected this response to motor planning and/or movement selection operations, but to date such studies have examined only the early aspects of the response (i.e., before movement) and a limited number of parameters. In this study, we used magnetoencephalography (MEG) and a novel motor sequence paradigm to probe how motor plan complexity modulates peri-movement beta oscillations, and connectivity within activated circuits. We also examined the dynamics by imaging beta activity before and during movement execution and extracting virtual sensors from key regions. We found stronger beta desynchronization during complex relative to simple sequences in the right parietal and left dorsolateral prefrontal cortex (DLPFC) during movement execution. There was also an increase in functional connectivity between the left DLPFC and right parietal shortly after movement onset during complex but not simple sequences, which produced a significant conditional effect (i.e., complex > simple) that was not attributable to differences in response amplitude. This study is the first to demonstrate that complexity modulates the dynamics of the peri-movement beta ERD, which provides crucial new data on the functional role of this well-known oscillatory motor response. These data further suggest that execution of complex motor behavior may recruit key regions of the fronto-parietal network, in addition to traditional sensorimotor regions.

Spatiotemporal oscillatory dynamics during the encoding and maintenance phases of a visual working memory task

Many electrophysiology studies have examined neural oscillatory activity during the encoding, maintenance, and/or retrieval phases of various working memory tasks. Together, these studies have helped illuminate the underlying neural dynamics, although much remains to be discovered and some findings have not replicated in subsequent work. In this study, we examined the oscillatory dynamics that serve visual working memory operations using high-density magnetoencephalography (MEG) and advanced time-frequency and beamforming methodology. Specifically, we recorded healthy adults while they performed a high-load, Sternberg-type working memory task, and focused on the encoding and maintenance phases. We found significant 9-16 Hz desynchronizations in the bilateral occipital cortices, left dorsolateral prefrontal cortex (DLPFC), and left superior temporal areas throughout the encoding phase. Our analysis of the dynamics showed that the left DLPFC and superior temporal desynchronization became stronger as a function of time during the encoding period, and was sustained throughout most of the maintenance phase until sharply decreasing in the milliseconds preceding retrieval. In contrast, desynchronization in occipital areas became weaker as a function of time during encoding and eventually evolved into a strong synchronization during the maintenance period, consistent with previous studies. These results provide clear evidence of dynamic network-level processes during the encoding and maintenance phases of working memory, and support the notion of a dynamic pattern of functionally-discrete subprocesses within each working memory phase. The presence of such dynamic oscillatory networks may be a potential source of inconsistent findings in this literature, as neural activity within these networks changes dramatically with time.

Neurophysiological abnormalities in the sensorimotor cortices during the motor planning and movement execution stages of children with cerebral palsy

AIM

This investigation used magnetoencephalography (MEG) to examine the neural oscillatory responses of the sensorimotor cortices during the motor planning and movement execution stages of children with typical development and children with cerebral palsy (CP).

METHOD

The study involved 13 children with CP (nine males, four females; mean [SD] age 14y 3mo [9mo], range 10-18y; height 1.61m [0.08m]; weight 52.65kg [13kg]), and 13 age- and sex-matched typically developing children (height 1.64m [0.06m]; weight 56.88kg [10kg]). The experiment required the children to extend their knee joint as whole-head MEG recordings were acquired. Beamformer imaging methods were employed to quantify the source activity of the beta-frequency (14-28Hz) event-related desynchronization (ERD) that occurs during the motor planning period, and the gamma-frequency (~50Hz) event-related synchronization (ERS) that occurs at the motor execution stage.

RESULTS

The children with CP had a stronger mean beta ERD during the motor planning phase and reduced mean gamma ERS at the onset of movement.

INTERPRETATION

The uncharacteristic beta ERD in the children with CP suggests that they may have greater difficulty planning knee joint movements. We suggest that these aberrant beta ERD oscillations may have a cascading effect on the gamma ERS, which ultimately affects the execution of the motor command.

Circadian modulation of motor-related beta oscillatory responses

Previous electrophysiological investigations have evaluated movement-related beta (14-28 Hz) oscillatory activity in healthy participants. These studies have described an abrupt decrease in beta activity that starts before movement onset, and a sharp increase in beta power that peaks after movement termination. These neural responses have been respectively termed the event-related beta desynchronization or pre-movement beta ERD, and the post-movement beta rebound (PMBR). Previous studies have shown that a variety of movement parameters and demographic factors (e.g., age) modulate the amplitude of these oscillatory responses, and in the current study we evaluated whether the amplitudes follow a biological temporal rhythm (e.g., circadian), as it is known that spontaneous beta levels increase from morning to afternoon in some brain areas. To this end, we used magnetoencephalography (MEG) to evaluate oscillatory activity during a right hand finger-tapping task in four participants who were recorded at three different times (09:00, 12:00, 16:00) on three consecutive days (i.e., 36 total MEG sessions). All MEG data were corrected for head motion and examined in the time-frequency domain using beamforming methods. We found a significant linear increase in beta ERD amplitude from 09:00 to 16:00 h in the left precentral gyrus, left premotor cortices, left supplementary motor area (SMA), and right precentral and postcentral gyri. In contrast, the amplitude of the PMBR was very steady across the day in all brain regions except the left SMA, which exhibited a linear increase from morning to afternoon. Finally, beta levels during the baseline period also increased from 09:00 to 16:00 in most regions of the cortical sensorimotor network. These data show that both the pre-movement beta ERD and spontaneous beta levels strongly increase from morning to afternoon in the motor cortices, which may indicate that the amplitude of the beta ERD response is determined by the spontaneous beta level during the motor planning period.

Movement-related neuromagnetic fields in preschool age children

We examined sensorimotor brain activity associated with voluntary movements in preschool children using a customized pediatric magnetoencephalographic system. A videogame-like task was used to generate self-initiated right or left index finger movements in 17 healthy right-handed subjects (8 females, ages 3.2-4.8 years). We successfully identified spatiotemporal patterns of movement-related brain activity in 15/17 children using beamformer source analysis and surrogate MRI spatial normalization. Readiness fields in the contralateral sensorimotor cortex began ∼0.5 s prior to movement onset (motor field, MF), followed by transient movement-evoked fields (MEFs), similar to that observed during self-paced movements in adults, but slightly delayed and with inverted source polarities. We also observed modulation of mu (8-12 Hz) and beta (15-30 Hz) oscillations in sensorimotor cortex with movement, but with different timing and a stronger frequency band coupling compared to that observed in adults. Adult-like high-frequency (70-80 Hz) gamma bursts were detected at movement onset. All children showed activation of the right superior temporal gyrus that was independent of the side of movement, a response that has not been reported in adults. These results provide new insights into the development of movement-related brain function, for an age group in which no previous data exist. The results show that children under 5 years of age have markedly different patterns of movement-related brain activity in comparison to older children and adults, and indicate that significant maturational changes occur in the sensorimotor system between the preschool years and later childhood.

EEG changes caused by spontaneous facial self-touch may represent emotion regulating processes and working memory maintenance

Spontaneous facial self-touch gestures (sFSTG) are performed manifold every day by every human being, primarily in stressful situations. These movements are not usually designed to communicate and are frequently accomplished with little or no awareness. The aim of the present study was to investigate whether sFSTG are associated with specific changes in the electrical brain activity that might indicate an involvement of regulatory emotional processes and working memory. Fourteen subjects performed a delayed memory task of complex haptic stimuli. The stimuli had to be explored and then remembered for a retention interval of 5min. The retention interval was interrupted by unpleasant sounds from The International Affective Digitized Sounds and short sound-free periods. During the experiment a video stream of behavior, 19-channel EEG, and EMG (of forearm muscles) were recorded. Comparisons of the behavioral data and spectral power of different EEG frequency bands (theta, alpha, beta, and gamma) were conducted. An increase of sFSTG during the application of unpleasant sounds was observed. A significant increase of spectral theta and beta power was observed after exploration of the stimuli as well as after sFSTG in centro-parietal electrodes. The spectral theta power extremely decreased just before sFSTG during the retention interval. Contrary to this, no significant changes were detected in any of the frequencies when the spectral power before and after instructed facial self-touch movements (b-iFSTG and a-iFSTG) were compared. The changes of spectral theta power in the intervals before and after sFSTG in centro-parietal electrodes imply that sFSTG are associated with cortical regulatory processes in the domains of working memory and emotions.

Aberrant synchrony in the somatosensory cortices predicts motor performance errors in children with cerebral palsy

Cerebral palsy (CP) results from a perinatal brain injury that often results in sensory impairments and greater errors in motor performance. Although these impairments have been well catalogued, the relationship between sensory processing networks and errors in motor performance has not been well explored. Children with CP and typically developing age-matched controls participated in this investigation. We used high-density magnetoencephalography to measure event-related oscillatory changes in the somatosensory cortices following tactile stimulation to the bottom of the foot. In addition, we quantified the amount of variability or errors in the isometric ankle joint torques as these children attempted to match a target. Our results showed that neural populations in the somatosensory cortices of children with CP were desynchronized by the tactile stimulus, whereas those of typically developing children were clearly synchronized. Such desynchronization suggests that children with CP were unable to fully integrate the external stimulus into ongoing sensorimotor computations. Our results also indicated that children with CP had a greater amount of errors in their motor output when they attempted to match the target force, and this amount of error was negatively correlated with the degree of synchronization present in the somatosensory cortices. These results are the first to show that the motor performance errors of children with CP are linked with neural synchronization within the somatosensory cortices.

MEG studies of motor cortex gamma oscillations: evidence for a gamma "fingerprint" in the brain?

The human motor cortex exhibits transient bursts of high frequency gamma oscillations in the 60–90 Hz range during movement. It has been proposed that gamma oscillations generally reflect local intracortical activity. However, movement-evoked gamma is observed simultaneously in both cortical and subcortical (basal ganglia) structures and thus appears to reflect long-range cortical-subcortical interactions. Recent evidence suggests that gamma oscillations do not simply reflect sensory reafference, but have a facilitative role in movement initiation. Here we summarize contributions of MEG to our understanding of movement-evoked gamma oscillations, including evidence that transient gamma bursts during the performance of specific movements constitutes a stereotyped spectral and temporal pattern within individuals—a gamma “fingerprint”—that is highly stable over time. Although their functional significance remains to be fully understood, movement-evoked gamma oscillations may represent frequency specific tuning within cortical-subcortical networks that can be monitored non-invasively using MEG during a variety of motor tasks, and may provide important information regarding cortical dynamics of ongoing motor control.

Functional brain abnormalities during finger-tapping in HIV-infected older adults: a magnetoencephalography study

Despite the availability of combination antiretroviral therapy, at least mild cognitive dysfunction is commonly observed in HIV-infected patients, with an estimated prevalence of 35-70 %. Neuropsychological studies of these HIV-associated neurocognitive disorders (HAND) have documented aberrations across a broad range of functional domains, although the basic pathophysiology remains unresolved. Some of the most common findings have been deficits in fine motor control and reduced psychomotor speed, but to date no neuroimaging studies have evaluated basic motor control in HAND. In this study, we used magnetoencephalography (MEG) to evaluate the neurophysiological processes that underlie motor planning in older HIV-infected adults and a matched, uninfected control group. MEG is a noninvasive and direct measure of neural activity with good spatiotemporal precision. During the MEG recording, participants fixated on a central crosshair and performed a finger-tapping task with the dominant hand. All MEG data was corrected for head movements, preprocessed, and imaged in the time-frequency domain using beamforming methodology. All analyses focused on the pre-movement beta desynchronization, which is known to be an index of movement planning. Our results demonstrated that HIV-1-infected patients have deficient beta desynchronization relative to controls within the left/right precentral gyri, and the supplementary motor area. In contrast, HIV-infected persons showed abnormally strong beta responses compared to controls in the right dorsolateral prefrontal cortex and medial prefrontal areas. In addition, the amplitude of beta activity in the primary and supplementary motor areas correlated with scores on the Grooved Pegboard test in HIV-infected adults. These results demonstrate that primary motor and sensory regions may be particularly vulnerable to HIV-associated damage, and that prefrontal cortices may serve a compensatory role in maintaining motor performance levels in infected patients.

Neuromagnetic evidence of abnormal movement-related beta desynchronization in Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder associated with debilitating motor, posture, and gait abnormalities. Human studies recording local field potentials within the subthalamic nucleus and scalp-based electroencephalography have shown pathological beta synchronization throughout the cortical–basal ganglia motor network in PD. Suppression of such pathological beta synchronization has been associated with improved motor function, which may explain the effectiveness of deep-brain stimulation. We used magnetoencephalography (MEG) to investigate neural population-level beta responses, and other oscillatory activity, during a motor task in unmedicated patients with PD and a matched group of healthy adults. MEG is a noninvasive neurophysiological technique that permits the recording of oscillatory activity during movement planning, execution, and termination phases. Each of these phases was independently examined using beamforming to distinguish the brain areas and movement phases, where pathological oscillations exist during motor control. Patients with PD exhibited significantly diminished beta desynchronization compared with controls prior to and during movement, which paralleled reduced alpha desynchronization. This study is the first to systematically investigate neural oscillatory responses in PD during distinct stages of motor control (e.g. planning, execution, and termination) and indicates that these patients have significant difficulty suppressing cortical beta synchronization during movement planning, which may contribute to their diminished movement capacities.

Oscillatory activity of the human cerebellum: the intracranial electrocerebellogram revisited

The functional electrophysiology of the human cerebellum remains poorly characterized. Existing knowledge originates primarily from lesion studies and increasingly from hemodynamic measures such as functional magnetic resonance imaging, along with some evidence in recent years from transcranial magnetic stimulation. In this context, we revisit the few existing records of intracranial recordings from the human cerebellum, and uncover additional little-known reports - three from the Soviet Union, published in Russian between 1949 and 1951, and one from Belgium, published in French in 1964. These studies together demonstrate electrical rhythms of the human cerebellar cortex at frequencies as high as 250 Hz, including task-related modulations. A reanalysis of their electrode traces with state-of-the-art spectral analysis techniques confirm the reported frequency bands, and showed that these modulations were sustained for 100-200 ms. These remarkable observations from the early ages of intracranial mapping of the human brain are in line with recent electrophysiological studies of oscillations in the rodent cerebellum as well as magnetoencephalographic findings in humans. Time-frequency analyses have provided valuable insight into the function of cerebral cortex, and may prove even more critical for the differing neurophysiology of the cerebellum. We contend that these insights will be invaluable to bridge the role of oscillatory networks in the cerebellum with those of cerebral cortex in mediating perception, action, and cognition and to investigate possible cerebellar involvement in neurological dysfunction.

Aberrant Oscillatory Activity during Simple Movement in Task-Specific Focal Hand Dystonia

In task-specific focal hand dystonia (tspFHD), the temporal dynamics of cortical activity in the motor system and how these processes are related to impairments in sensory and motor function are poorly understood. Here, we use time-frequency reconstructions of magnetoencephalographic (MEG) data to elaborate the temporal and spatial characteristics of cortical activity during movement. A self-paced finger tapping task during MEG recording was performed by 11 patients with tspFHD and 11 matched healthy controls. In both groups robust changes in beta (12-30 Hz) and high gamma (65-90 Hz) oscillatory activity were identified over sensory and motor cortices during button press. A significant decrease [p < 0.05, 1% False Discovery Rate (FDR) corrected] in high gamma power during movements of the affected hand was identified over ipsilateral sensorimotor cortex in the period prior to (-575 ms) and following (725 ms) button press. Furthermore, an increase (p < 0.05, 1% FDR corrected) in beta power suppression following movement of the affected hand was identified over visual cortex in patients with tspFHD. For movements of the unaffected hand, a significant (p < 0.05, 1% FDR corrected) increase in beta power suppression was identified over secondary somatosensory cortex (S2) in the period following button press in patients with tspFHD. Oscillatory activity within in the tspFHD group was however not correlated with clinical measures. Understanding these aberrant oscillatory dynamics can provide the groundwork for interventions that focus on modulating the timing of this activity.

Coactivation of lower leg muscles during body weight-supported treadmill walking decreases with age in adolescents

The kinematics of children's walking are nearly adult-like by about age 3-4 years, but metabolic efficiency of walking does not reach adult values until late in adolescence or early adulthood, perhaps due to higher coactivation of agonist/antagonist muscle pairs in adolescents. Additionally, it is unknown how use of a body weight-supported treadmill device affects coactivation, but because unloading will alter the activity of anti-gravity muscles, it was hypothesized that muscle coactivation will be altered as well. Muscle coactivation during treadmill walking was evaluated for adolescents (ages 10 to 17 years, M = 13.2, SD = 2.2) and adults (ages 22 to 35 years, M = 25.2, SD = 4.3), for thigh muscles (vastus lateralis/biceps femoris) and lower leg muscles (tibialis anterior/gastrocnemius). Conditions included body weight unloadings from nearly 0% to 80% of body weight, while walking at a preferred speed (self-selected, overground speed) or a reduced speed. Unloading was accomplished using a lower body positive pressure support system. Coactivation was found to be higher in adolescents than in adults, but only for the lower leg muscles.

Neural correlates of delayed visual-motor performance in children treated for brain tumours

Both structural and functional neural integrity is critical for healthy cognitive function and performance. Across studies, it is evident that children who are affected by neurological insult commonly demonstrate impaired cognitive abilities. Children treated with cranial radiation for brain tumours suffer substantial structural damage and exhibit a particularly high correlation between the degree of neural injury and cognitive deficits. However the pathophysiology underlying impaired cognitive performance in this population, and many other paediatric populations affected by neurological injury or disease, is unknown. We wished to investigate the characteristics of neuronal function during visual-motor task performance in a group of children who were treated with cranial radiation for brain tumours. We used Magnetoencephalography to investigate neural function during visual-motor reaction time (RT) task performance in 15 children treated with cranial radiation for Posterior Fossa malignant brain tumours and 17 healthy controls. We found that, relative to controls, the patient group showed: 1) delayed latencies for neural activation in both visual and motor cortices; 2) muted motor responses in the alpha (8-12Hz) and beta (13-29Hz) bandwidths, and 3) potentiated visual and motor responses in the gamma (30-100Hz) bandwidth. Collectively these observations indicate impaired neural processing during visual-motor RT performance in this population and that delays in the speed of visual and motor neuronal processing both contribute to the delays in the behavioural response. As increases in gamma activity are often observed with increases in attention and effort, increased gamma activities in the patient group may reflect compensatory neural activity during task performance. This is the first study to investigate neural function in real-time during cognitive performance in paediatric brain tumour patients.