Dynamic interactions in the fronto-parietal network during a manual stimulus-response compatibility task

Single-Trial Electroencephalography Discrimination of Real, Regulated, Isometric Wrist Extension and Wrist Flexion

Improved interpretation of electroencephalography (EEG) associated with the neural control of essential hand movements, including wrist extension (WE) and wrist flexion (WF), could improve the performance of brain-computer interfaces (BCIs). These BCIs could control a prosthetic or orthotic hand to enable motor-impaired individuals to regain the performance of activities of daily living. This study investigated the interpretation of neural signal patterns associated with kinematic differences between real, regulated, isometric WE and WF movements from recorded EEG data. We used 128-channel EEG data recorded from 14 participants performing repetitions of the wrist movements, where the force, speed, and range of motion were regulated. The data were filtered into four frequency bands: delta and theta, mu and beta, low gamma, and high gamma. Within each frequency band, independent component analysis was used to isolate signals originating from seven cortical regions of interest. Features were extracted from these signals using a time-frequency algorithm and classified using Mahalanobis distance clustering. We successfully classified bilateral and unilateral WE and WF movements, with respective accuracies of 90.68% and 69.80%. The results also demonstrated that all frequency bands and regions of interest contained motor-related discriminatory information. Bilateral discrimination relied more on the mu and beta bands, while unilateral discrimination favoured the gamma bands. These results suggest that EEG-based BCIs could benefit from the extraction of features from multiple frequencies and cortical regions.

Impact of data processing varieties on DCM estimates of effective connectivity from task-fMRI

Effective connectivity (EC) refers to directional or causal influences between interacting neuronal populations or brain regions and can be estimated from functional magnetic resonance imaging (fMRI) data via dynamic causal modeling (DCM). In contrast to functional connectivity, the impact of data processing varieties on DCM estimates of task-evoked EC has hardly ever been addressed. We therefore investigated how task-evoked EC is affected by choices made for data processing. In particular, we considered the impact of global signal regression (GSR), block/event-related design of the general linear model (GLM) used for the first-level task-evoked fMRI analysis, type of activation contrast, and significance thresholding approach. Using DCM, we estimated individual and group-averaged task-evoked EC within a brain network related to spatial conflict processing for all the parameters considered and compared the differences in task-evoked EC between any two data processing conditions via between-group parametric empirical Bayes (PEB) analysis and Bayesian data comparison (BDC). We observed strongly varying patterns of the group-averaged EC depending on the data processing choices. In particular, task-evoked EC and parameter certainty were strongly impacted by GLM design and type of activation contrast as revealed by PEB and BDC, respectively, whereas they were little affected by GSR and the type of significance thresholding. The event-related GLM design appears to be more sensitive to task-evoked modulations of EC, but provides model parameters with lower certainty than the block-based design, while the latter is more sensitive to the type of activation contrast than is the event-related design. Our results demonstrate that applying different reasonable data processing choices can substantially alter task-evoked EC as estimated by DCM. Such choices should be made with care and, whenever possible, varied across parallel analyses to evaluate their impact and identify potential convergence for robust outcomes.

Approach-avoidance behavior and motor-specific modulation towards smoking-related cues in smokers

AIMS

By performing three transcranial magnetic stimulation (TMS) experiments, we measured the motor-specific modulatory mechanisms in the primary motor cortex (M1) at both the intercortical and intracortical levels when smokers actively approach or avoid smoking-related cues.

DESIGN, SETTING AND PARTICIPANTS

For all experiments, the design was group (smokers versus non-smokers) × action (approach versus avoidance) × image type (neutral versus smoking-related). The study was conducted at the Shanghai University of Sport, CHN, TMS Laboratory. For experiment 1, 30 non-smokers and 30 smokers; for experiment 2, 16 non-smokers and 16 smokers; for experiment 3, 16 non-smokers and 16 smokers.

MEASUREMENTS

For all experiments, the reaction times were measured using the smoking stimulus-response compatibility task. While performing the task, single-pulse TMS was applied to the M1 in experiment 1 to measure the excitability of the corticospinal pathways, and paired-pulse TMS was applied to the M1 in experiments 2 and 3 to measure the activity of intracortical facilitation (ICF) and short-interval intracortical inhibition (SICI) circuits, respectively.

FINDINGS

Smokers had faster responses when approaching smoking-related cues (F1,58  = 36.660, P < 0.001, η p 2  = 0.387), accompanied by higher excitability of the corticospinal pathways (F1,58  = 10.980, P = 0.002, η p 2  = 0.159) and ICF circuits (F1,30  = 22.187, P < 0.001, η p 2  = 0.425), while stronger SICI effects were observed when they avoided these cues (F1,30  = 10.672, P = 0.003, η p 2  = 0.262).

CONCLUSIONS

Smokers appear to have shorter reaction times, higher motor-evoked potentials and stronger intracortical facilitation effects when performing approach responses to smoking-related cues and longer reaction times, a lower primary motor cortex descending pathway excitability and a stronger short-interval intracortical inhibition effect when avoiding them.

Functional and Structural Architectures of Allocentric and Egocentric Spatial Coding in Aging: A Combined DTI and fMRI Study

Background

Aging disrupts the optimal balance between neural nodes underlying orienting and attention control functions. Previous studies have suggested that age-related changes in cognitive process are associated to the changes in the myelinated fiber bundles, which affected the speed and actions of the signal propagation across different neural networks. However, whether the age-related difference in allocentric and egocentric spatial coding is accounted by the difference in white-matter integrity is unclear. In this study, using diffusion tensor imaging (DTI) and functional magnetic resonance imaging (fMRI), we sought to elucidate whether age-related differences in white matter integrity accounts for the difference in nodes to the distributed spatial coding-relevant brain networks.

Material and Method

Older (n = 24) and younger (n = 27) participants completed the structural DTI and fMRI scans during which they engaged in a cue-to-target task to elicit allocentric or egocentric processes.

Results and Conclusion

Efficient modulation of both allocentric and egocentric spatial coding in fronto-parietal attention network (FPAN) requires structure–function interaction. Allocentric task-modulated connectivity of the fronto-parietal network (FPN) and dorsal attention network (DAN) with the temporal lobe was influenced by the aging differences of the white-matter tracts of the posterior and superior corona radiata (PCR and SCR), respectively. On the other hand, aging difference of the superior longitudinal fasciculus mainly influenced the egocentric-task-modulated connections of the DAN and FPN with frontal regions and posterior cingulate cortex. This study suggested that functional connections of the FPAN with near and far task-relevant nodes vary significantly with age and conditions.

Characteristics inhibition defects of children with developmental dyscalculia: Evidence from the ERP

Developmental dyscalculia (DD) is characterized by insufficient mathematical learning ability and weaker mathematical performance than peers who are developmentally typical. As a subtype of learning disability, developmental dyscalculia contributes to deep cognitive processing deficits, mainly manifested as a lack of numerical processing ability. This study utilized event-related potentials (ERPs) technology to examine the negative priming effects (NP) between children with and without DD. Behaviorally, trends in mean reaction time (RT) were consistent between children with and without DD under prime and control conditions. The developmental dyscalculia group and the typical developmental (TD) children group showed a significant negative priming effect. However, the magnitude of the NP was significantly different between two groups, with the magnitude being significantly higher in the TD group than the DD group. In terms of the ERPs results, there were significantly larger amplitudes of P100, P200, and P300 in the TD group than that of children with DD. At the same time, in the DD group, N100 and P300 latency were significantly delayed in some electrodes than the TD group. The results indicated that there were characteristic inhibition deficits in children with DD. Inhibition defects in children with DD might be the underlying cause of the development of digital processing ability of children with DD.

Increased prefrontal top-down control in older adults predicts motor performance and age-group association

Bimanual motor control declines during ageing, affecting the ability of older adults to maintain independence. An important underlying factor is cortical atrophy, particularly affecting frontal and parietal areas in older adults. As these regions and their interplay are highly involved in bimanual motor preparation, we investigated age-related connectivity changes between prefrontal and premotor areas of young and older adults during the preparatory phase of complex bimanual movements using high-density electroencephalography. Generative modelling showed that excitatory inter-hemispheric prefrontal to premotor coupling in older adults predicted age-group affiliation and was associated with poor motor-performance. In contrast, excitatory intra-hemispheric prefrontal to premotor coupling enabled older adults to maintain motor-performance at the cost of lower movement speed. Our results disentangle the complex interplay in the prefrontal-premotor network during movement preparation underlying reduced bimanual control and the well-known speed-accuracy trade-off seen in older adults.

Conflict processing networks: A directional analysis of stimulus-response compatibilities using MEG

The suppression of distracting information in order to focus on an actual cognitive goal is a key feature of executive functions. The use of brain imaging methods to investigate the underlying neurobiological brain activations that occur during conflict processing have demonstrated a strong involvement of the fronto-parietal attention network (FPAN). Surprisingly, the directional interconnections, their time courses and activations at different frequency bands remain to be elucidated, and thus, this constitutes the focus of this study. The shared information flow between brain areas of the FPAN is provided for frequency bands ranging from the theta to the lower gamma band (4–40 Hz). We employed an adaptation of the Simon task utilizing Magnetoencephalography (MEG). Granger causality was applied to investigate interconnections between the active brain regions, as well as their directionality. Following stimulus onset, the middle frontal precentral cortex and superior parietal cortex were significantly activated during conflict processing in a time window of between 300 to 600ms. Important differences in causality were found across frequency bands between processing of conflicting stimuli in the left as compared to the right visual hemifield. The exchange of information from and to the FPAN was most prominent in the beta band. Moreover, the anterior cingulate cortex and the anterior insula represented key areas for conflict monitoring, either by receiving input from other areas of the FPAN or by generating output themselves. This indicates that the salience network is at least partly involved in processing conflict information. The present study provides detailed insights into the underlying neural mechanisms of the FPAN, especially regarding its temporal characteristics and directional interconnections.

Involvement of the primary motor cortex in the early processing stage of the affective stimulus-response compatibility effect in a manikin task

Compatible (positive approaching and negative avoiding) and incompatible (positive avoiding and negative approaching) behavior are of great significance for biological adaptation and survival. Previous research has found that reaction times of compatible behavior are shorter than the incompatible behavior, which is termed the stimulus-response compatibility (SRC) effect. However, the underlying neurophysiological mechanisms of the SRC effect applied to affective stimuli is still unclear. Here, we investigated preparatory activities in both the left and right primary motor cortex (M1) before the execution of an approaching-avoiding behavior using the right index finger in a manikin task based on self-identity. The results showed significantly shorter reaction times for compatible than incompatible behavior. Most importantly, motor-evoked potential (MEP) amplitudes from left M1 stimulation were significantly higher during compatible behavior than incompatible behavior at 150 and 200 ms after stimulus presentation, whereas the reversed was observed for right M1 stimulation with lower MEP amplitude in compatible compared to incompatible behavior at 150 ms. The current findings revealed the compatibility effect at both behavioral and neurophysiological levels, indicating that the affective SRC effect occurs early in the motor cortices during stimulus processing, and MEP modulation at this early processing stage could be a physiological marker of the affective SRC effect.

Functional connectivity during monitoring for visuomotor incongruence

Previous human studies on monitoring for visuomotor incongruence emphasized the contribution of the fronto-parietal network and revealed significant activation of the right dorsolateral prefrontal cortex (DLPFC) and the right rostral inferior parietal lobule. Using functional MRI, this study investigated the brain regions involved in explicit monitoring for incongruence between motor intention and visual and/or proprioceptive information, particularly focusing on the fronto-parietal network. During in-phase bimanual movements, a static image of the participant's own hands was randomly inserted within real-time visual feedback of the movements to produce a mismatch between the actual performance and the visual input. The results of our task were similar to those of previous studies, in that greater activity was observed in the right DLPFC during incongruence conditions than during congruence conditions. However, the anatomical location of the DLPFC cluster was found in a more ventral region, compared with previous studies. Psychophysiological interaction analysis for the entire brain, using the right DLPFC as a seed region, indicated significantly greater functional connectivity with the bilateral dorsal premotor cortex, middle temporal gyri (area V5), and right rostral inferior parietal lobule (area PFt).

Multivariate Classification of Major Depressive Disorder Using the Effective Connectivity and Functional Connectivity

Major depressive disorder (MDD) is a mental disorder characterized by at least 2 weeks of low mood, which is present across most situations. Diagnosis of MDD using rest-state functional magnetic resonance imaging (fMRI) data faces many challenges due to the high dimensionality, small samples, noisy and individual variability. To our best knowledge, no studies aim at classification with effective connectivity and functional connectivity measures between MDD patients and healthy controls. In this study, we performed a data-driving classification analysis using the whole brain connectivity measures which included the functional connectivity from two brain templates and effective connectivity measures created by the default mode network (DMN), dorsal attention network (DAN), frontal-parietal network (FPN), and silence network (SN). Effective connectivity measures were extracted using spectral Dynamic Causal Modeling (spDCM) and transformed into a vectorial feature space. Linear Support Vector Machine (linear SVM), non-linear SVM, k-Nearest Neighbor (KNN), and Logistic Regression (LR) were used as the classifiers to identify the differences between MDD patients and healthy controls. Our results showed that the highest accuracy achieved 91.67% (p < 0.0001) when using 19 effective connections and 89.36% when using 6,650 functional connections. The functional connections with high discriminative power were mainly located within or across the whole brain resting-state networks while the discriminative effective connections located in several specific regions, such as posterior cingulate cortex (PCC), ventromedial prefrontal cortex (vmPFC), dorsal cingulate cortex (dACC), and inferior parietal lobes (IPL). To further compare the discriminative power of functional connections and effective connections, a classification analysis only using the functional connections from those four networks was conducted and the highest accuracy achieved 78.33% (p < 0.0001). Our study demonstrated that the effective connectivity measures might play a more important role than functional connectivity in exploring the alterations between patients and health controls and afford a better mechanistic interpretability. Moreover, our results showed a diagnostic potential of the effective connectivity for the diagnosis of MDD patients with high accuracies allowing for earlier prevention or intervention.

Network connectivity of motor control in the ageing brain

Older individuals typically display stronger regional brain activity than younger subjects during motor performance. However, knowledge regarding age-related changes of motor network interactions between brain regions remains scarce. We here investigated the impact of ageing on the interaction of cortical areas during movement selection and initiation using dynamic causal modelling (DCM). We found that age-related psychomotor slowing was accompanied by increases in both regional activity and effective connectivity, especially for ‘core’ motor coupling targeting primary motor cortex (M1). Interestingly, younger participants within the older group showed strongest connectivity targeting M1, which steadily decreased with advancing age. Conversely, prefrontal influences on the motor system increased with advancing age, and were inversely correlated with reduced parietal influences and core motor coupling. Interestingly, higher net coupling within the prefrontal-premotor-M1 axis predicted faster psychomotor speed in ageing. Hence, as opposed to a uniform age-related decline, our findings are compatible with the idea of different age-related compensatory mechanisms, with an important role of the prefrontal cortex compensating for reduced coupling within the core motor network.

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Enhanced motor network activity and connectivity in ageing

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Parietal-premotor and premotor-M1 coupling decreases with advancing age.

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Prefrontal influences on the motor system increase with advancing age.

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Prefrontal cortex compensates for age-related decline in other motor connections.

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Prefrontal-premotor-M1 coupling predicts psychomotor speed in ageing.

Subtypes and comorbidity in mathematical learning disabilities: Multidimensional study of verbal and visual memory processes is key to understanding

A large body of research suggests that mathematical learning disability (MLD) is related to working memory impairment. Here, I organize part of this literature through a meta-analysis of 36 studies with 665 MLD and 1049 control participants. I demonstrate that one subtype of MLD is associated with reading problems and weak verbal short-term and working memory. Another subtype of MLD does not have associated reading problems and is linked to weak visuospatial short-term and working memory. In order to better understand MLD we need to precisely define potentially modality-specific memory subprocesses and supporting executive functions, relevant for mathematical learning. This can be achieved by taking a multidimensional parametric approach systematically probing an extended network of cognitive functions. Rather than creating arbitrary subgroups and/or focus on a single factor, highly powered studies need to position individuals in a multidimensional parametric space. This will allow us to understand the multidimensional structure of cognitive functions and their relationship to mathematical performance.

Multimodal connectivity of motor learning-related dorsal premotor cortex

The dorsal premotor cortex (dPMC) is a key region for motor learning and sensorimotor integration, yet we have limited understanding of its functional interactions with other regions. Previous work has started to examine functional connectivity in several brain areas using resting state functional connectivity (RSFC) and meta-analytical connectivity modelling (MACM). More recently, structural covariance (SC) has been proposed as a technique that may also allow delineation of functional connectivity. Here, we applied these three approaches to provide a comprehensive characterization of functional connectivity with a seed in the left dPMC that a previous meta-analysis of functional neuroimaging studies has identified as playing a key role in motor learning. Using data from two sources (the Rockland sample, containing resting state data and anatomical scans from 132 participants, and the BrainMap database, which contains peak activation foci from over 10,000 experiments), we conducted independent whole-brain functional connectivity mapping analyses of a dPMC seed. RSFC and MACM revealed similar connectivity maps spanning prefrontal, premotor, and parietal regions, while the SC map identified more widespread frontal regions. Analyses indicated a relatively consistent pattern of functional connectivity between RSFC and MACM that was distinct from that identified by SC. Notably, results indicate that the seed is functionally connected to areas involved in visuomotor control and executive functions, suggesting that the dPMC acts as an interface between motor control and cognition.

Neural networks supporting switching, hypothesis testing, and rule application

We identified dynamic changes in recruitment of neural connectivity networks across three phases of a flexible rule learning and set-shifting task similar to the Wisconsin Card Sort Task: switching, rule learning via hypothesis testing, and rule application. During fMRI scanning, subjects viewed pairs of stimuli that differed across four dimensions (letter, color, size, screen location), chose one stimulus, and received feedback. Subjects were informed that the correct choice was determined by a simple unidimensional rule, for example "choose the blue letter". Once each rule had been learned and correctly applied for 4-7 trials, subjects were cued via either negative feedback or visual cues to switch to learning a new rule. Task performance was divided into three phases: Switching (first trial after receiving the switch cue), hypothesis testing (subsequent trials through the last error trial), and rule application (correct responding after the rule was learned). We used both univariate analysis to characterize activity occurring within specific regions of the brain, and a multivariate method, constrained principal component analysis for fMRI (fMRI-CPCA), to investigate how distributed regions coordinate to subserve different processes. As hypothesized, switching was subserved by a limbic network including the ventral striatum, thalamus, and parahippocampal gyrus, in conjunction with cortical salience network regions including the anterior cingulate and frontoinsular cortex. Activity in the ventral striatum was associated with switching regardless of how switching was cued; visually cued shifts were associated with additional visual cortical activity. After switching, as subjects moved into the hypothesis testing phase, a broad fronto-parietal-striatal network (associated with the cognitive control, dorsal attention, and salience networks) increased in activity. This network was sensitive to rule learning speed, with greater extended activity for the slowest learning speed late in the time course of learning. As subjects shifted from hypothesis testing to rule application, activity in this network decreased and activity in the somatomotor and default mode networks increased.

Effective connectivity within the frontoparietal control network differentiates cognitive control and working memory

Cognitive control and working memory rely upon a common fronto-parietal network that includes the inferior frontal junction (IFJ), dorsolateral prefrontal cortex (dlPFC), pre-supplementary motor area/dorsal anterior cingulate cortex (pSMA/dACC), and intraparietal sulcus (IPS). This network is able to flexibly adapt its function in response to changing behavioral goals, mediating a wide range of cognitive demands. Here we apply dynamic causal modeling to functional magnetic resonance imaging data to characterize task-related alterations in the strength of network interactions across distinct cognitive processes. Evidence in favor of task-related connectivity dynamics was accrued across a very large space of possible network structures. Cognitive control and working memory demands were manipulated using a factorial combination of the multi-source interference task and a verbal 2-back working memory task, respectively. Both were found to alter the sensitivity of the IFJ to perceptual information, and to increase IFJ-to-pSMA/dACC connectivity. In contrast, increased connectivity from the pSMA/dACC to the IPS, as well as from the dlPFC to the IFJ, was uniquely driven by cognitive control demands; a task-induced negative influence of the dlPFC on the pSMA/dACC was specific to working memory demands. These results reflect a system of both shared and unique context-dependent dynamics within the fronto-parietal network. Mechanisms supporting cognitive engagement, response selection, and action evaluation may be shared across cognitive domains, while dynamic updating of task and context representations within this network are potentially specific to changing demands on cognitive control.

Spatial and temporal functional connectivity changes between resting and attentive states

Remote brain regions show correlated spontaneous activity at rest within well described intrinsic connectivity networks (ICNs). Meta-analytic coactivation studies have uncovered networks similar to resting ICNs, suggesting that in task states connectivity modulations may occur principally within ICNs. However, it has also been suggested that specific "hub" regions dynamically link networks under different task conditions. Here, we used functional magnetic resonance imaging at rest and a continuous visual attention task in 16 participants to investigate whether a shift from rest to attention was reflected by within-network connectivity modulation, or changes in network topography. Our analyses revealed evidence for both modulation of connectivity within the default-mode (DMN) and dorsal attention networks (DAN) between conditions, and identified a set of regions including the temporoparietal junction (TPJ) and posterior middle frontal gyrus (MFG) that switched between the DMN and DAN depending on the task. We further investigated the temporal nonstationarity of flexible (TPJ and MFG) regions during both attention and rest. This showed that moment-to-moment differences in connectivity at rest mirrored the variation in connectivity between tasks. Task-dependent changes in functional connectivity of flexible regions may, therefore, be understood as shifts in the proportion of time specific connections are engaged, rather than a switch between networks per se. This ability of specific regions to dynamically link ICNs under different task conditions may play an important role in behavioral flexibility.

Anterior and posterior subareas of the dorsolateral frontal cortex in socially relevant decisions based on masked affect expressions

Socially-relevant decisions are based on clearly recognizable but also not consciously accessible affective stimuli. We studied the role of the dorsolateral frontal cortex (DLFC) in decision-making on masked affect expressions using functional magnetic resonance imaging. Our paradigm permitted us to capture brain activity during a pre-decision phase when the subjects viewed emotional expressions below the threshold of subjective awareness, and during the decision phase, which was based on verbal descriptions as the choice criterion. Using meta-analytic connectivity modeling, we found that the preparatory phase of the decision was associated with activity in a right-posterior portion of the DLFC featuring co-activations in the left-inferior frontal cortex. During the subsequent decision a right-anterior and more dorsal portion of the DLFC became activated, exhibiting a different co-activation pattern. These results provide evidence for partially independent sub-regions within the DLFC, supporting the notion of dual associative processes in intuitive judgments.

Anterior and posterior subareas of the dorsolateral frontal cortex in socially relevant decisions based on masked affect expressions

Socially-relevant decisions are based on clearly recognizable but also not consciously accessible affective stimuli. We studied the role of the dorsolateral frontal cortex (DLFC) in decision-making on masked affect expressions using functional magnetic resonance imaging. Our paradigm permitted us to capture brain activity during a pre-decision phase when the subjects viewed emotional expressions below the threshold of subjective awareness, and during the decision phase, which was based on verbal descriptions as the choice criterion. Using meta-analytic connectivity modeling, we found that the preparatory phase of the decision was associated with activity in a right-posterior portion of the DLFC featuring co-activations in the left-inferior frontal cortex. During the subsequent decision a right-anterior and more dorsal portion of the DLFC became activated, exhibiting a different co-activation pattern. These results provide evidence for partially independent sub-regions within the DLFC, supporting the notion of dual associative processes in intuitive judgments.

The role of top-down control in different phases of a sensorimotor timing task: a DCM study of adults and adolescents

The ability to precisely coordinate motor control to regularly-paced sensory stimuli requires an ability often called 'mental timekeeping', a distinct form of cognitive function. A consistent feature among conceptual models of the internal clock mechanism is an element of 'top-down' cognitive control. Although lesion and fMRI studies have provided indirect evidence supporting the role of the prefrontal cortex in exerting top-down influence over lower-level sensory and motor regions, little direct evidence exists. We investigated changes in Dynamic Causal Modeling (DCM)-measured top-down control of sensorimotor timing during different phases of a unimanual, auditory-paced finger-tapping task in a cohort of healthy adults and adolescents. The brain regions examined were organized into a network of excitatory connections between bilateral dorso- and ventrolateral prefrontal cortices and motor and auditory cortices. This baseline connectivity changed depending on whether participants listened passively to the pacing cue, synchronized their regular interval finger tapping with the cue, or continued tapping in absence of the cue. Subjects who performed better at maintaining the prescribed tapping pace in the absence of the auditory cue relied more on top-down control of the motor and sensory regions, while those with less accurate performance relied more on sensory driven, bottom-up control of the motor cortex. No significant maturational effects were observed in either the behavioral or DCM path weight data. Both right and left prefrontal cortex were found to exert control over timing behavioral accuracy, but there were distinctly lateralized roles with respect to optimal performance.

Distant functional connectivity for bimanual finger coordination declines with aging: an fMRI and SEM exploration

Although bimanual finger coordination is known to decline with aging, it still remains unclear how exactly the neural substrates underlying the coordination differ between young and elderly adults. The present study focused on: (1) characterization of the functional connectivity within the motor association cortex which is required for successful bimanual finger coordination, and (2) to elucidate upon its age-related decline. To address these objectives, we utilized functional magnetic resonance imaging (fMRI) in combination with structural equation modeling (SEM). This allowed us to compare functional connectivity models between young and elderly age groups during a visually guided bimanual finger movement task using both stable in-phase and complex anti-phase modes. Our SEM exploration of functional connectivity revealed significant age-related differences in connections surrounding the PMd in the dominant hemisphere. In the young group who generally displayed accurate behavior, the SEM model for the anti-phase mode exhibited significant connections from the dominant PMd to the non-dominant SPL, and from the dominant PMd to the dominant S1. However, the model for the elderly group's anti-phase mode in which task performance dropped, did not exhibit significant connections within the aforementioned regions. These results suggest that: (1) the dominant PMd acts as an intermediary to invoke intense intra- and inter-hemispheric connectivity with distant regions among the higher motor areas including the dominant S1 and the non-dominant SPL in order to achieve successful bimanual finger coordination, and (2) the distant connectivity among the higher motor areas declines with aging, whereas the local connectivity within the bilateral M1 is enhanced for the complex anti-phase mode. The latter may underlie the elderly's decreased performance in the complex anti-phase mode of the bimanual finger movement task.

Aging and response conflict solution: behavioural and functional connectivity changes

Healthy aging has been found associated with less efficient response conflict solution, but the cognitive and neural mechanisms have remained elusive. In a two-experiment study, we first examined the behavioural consequences of this putative age-related decline for conflicts induced by spatial stimulus-response incompatibility. We then used resting-state functional magnetic resonance imaging data from a large, independent sample of adults (n = 399; 18-85 years) to investigate age differences in functional connectivity between the nodes of a network previously found associated with incompatibility-induced response conflicts in the very same paradigm. As expected, overcoming interference from conflicting response tendencies took longer in older adults, even after accounting for potential mediator variables (general response speed and accuracy, motor speed, visuomotor coordination ability, and cognitive flexibility). Experiment 2 revealed selective age-related decreases in functional connectivity between bilateral anterior insula, pre-supplementary motor area, and right dorsolateral prefrontal cortex. Importantly, these age effects persisted after controlling for regional grey-matter atrophy assessed by voxel-based morphometry. Meta-analytic functional profiling using the BrainMap database showed these age-sensitive nodes to be more strongly linked to highly abstract cognition, as compared with the remaining network nodes, which were more strongly linked to action-related processing. These findings indicate changes in interregional coupling with age among task-relevant network nodes that are not specifically associated with conflict resolution per se. Rather, our behavioural and neural data jointly suggest that healthy aging is associated with difficulties in properly activating non-dominant but relevant task schemata necessary to exert efficient cognitive control over action.

Developmental dyscalculia is related to visuo-spatial memory and inhibition impairment

Developmental dyscalculia is thought to be a specific impairment of mathematics ability. Currently dominant cognitive neuroscience theories of developmental dyscalculia suggest that it originates from the impairment of the magnitude representation of the human brain, residing in the intraparietal sulcus, or from impaired connections between number symbols and the magnitude representation. However, behavioral research offers several alternative theories for developmental dyscalculia and neuro-imaging also suggests that impairments in developmental dyscalculia may be linked to disruptions of other functions of the intraparietal sulcus than the magnitude representation. Strikingly, the magnitude representation theory has never been explicitly contrasted with a range of alternatives in a systematic fashion. Here we have filled this gap by directly contrasting five alternative theories (magnitude representation, working memory, inhibition, attention and spatial processing) of developmental dyscalculia in 9-10-year-old primary school children. Participants were selected from a pool of 1004 children and took part in 16 tests and nine experiments. The dominant features of developmental dyscalculia are visuo-spatial working memory, visuo-spatial short-term memory and inhibitory function (interference suppression) impairment. We hypothesize that inhibition impairment is related to the disruption of central executive memory function. Potential problems of visuo-spatial processing and attentional function in developmental dyscalculia probably depend on short-term memory/working memory and inhibition impairments. The magnitude representation theory of developmental dyscalculia was not supported.

Shifted neuronal balance during stimulus-response integration in schizophrenia: an fMRI study

Schizophrenia is characterized by marked deficits in executive and psychomotor functions, as demonstrated for goal-directed actions in the antisaccade task. Recent studies, however, suggest that this deficit represents only one manifestation of a general deficit in stimulus-response integration and volitional initiation of motor responses. We here used functional magnetic resonance imaging to investigate brain activation patterns during a manual stimulus-response compatibility task in 18 schizophrenic patients and 18 controls. We found that across groups incongruent vs. congruent responses recruited a bilateral network consisting of dorsal fronto-parietal circuits as well as bilateral anterior insula, dorsolateral prefrontal cortex (DLPFC) and the presupplementary motor area (preSMA). When testing for the main-effect across all conditions, patients showed significantly lower activation of the right DLPFC and, in turn, increased activation in a left hemispheric network including parietal and premotor areas as well as the preSMA. For incongruent responses patients showed significantly increased activation in a similar left hemispheric network, as well as additional activation in parietal and premotor regions in the right hemisphere. The present study reveals that hypoactivity in the right DLPFC in schizophrenic patients is accompanied by hyperactivity in several fronto-parietal regions associated with task execution. Impaired top-down control due to a dysfunctional DLPFC might thus be partly compensated by an up-regulation of task-relevant regions in schizophrenic patients.

Cross-frequency power coupling between hierarchically organized face-selective areas

Neural oscillations are linked to perception and behavior and may reflect mechanisms for long-range communication between brain areas. We developed a causal model of oscillatory dynamics in the face perception network using magnetoencephalographic data from 51 normal volunteers. This model predicted induced responses to faces by estimating oscillatory power coupling between source locations corresponding to bilateral occipital and fusiform face areas (OFA and FFA) and the right superior temporal sulcus (STS). These sources showed increased alpha and theta and decreased beta power as well as selective responses to fearful facial expressions. We then used Bayesian model comparison to compare hypothetical models, which were motivated by previous connectivity data and a well-known theory of temporal lobe function. We confirmed this theory in detail by showing that the OFA bifurcated into 2 independent, hierarchical, feedforward pathways, with fearful expressions modulating power coupling only in the more dorsal (STS) pathway. The power coupling parameters showed a common pattern over connections. Low-frequency bands showed same-frequency power coupling, which, in the dorsal pathway, was modulated by fearful faces. Also, theta power showed a cross-frequency suppression of beta power. This combination of linear and nonlinear mechanisms could reflect computational mechanisms in hierarchical feedforward networks.

Neural Correlates of Switching Attentional Focus during Finger Movements: An fMRI Study

Research on motor-related attentional foci suggests that switching from an internal to an external focus of attention has advantageous effects on motor performance whereas switching from an external to an internal focus has disadvantageous effects. We used functional magnetic resonance imaging to investigate the neural correlates of switching the focus of attention. Two experimental groups were trained to apply one focus direction – internal or external – on a previously learned finger tapping sequence. Participants with an internal focus training were instructed to attend to their moving fingers; those with an external focus training were instructed to attend to the response buttons. In the first half of the experiment, participants performed with their trained focus, in the second half, they were unexpectedly asked to switch to the untrained attentional focus. Our data showed that the switch from a trained internal to an unfamiliar external focus of attention elicited increased activation of the left lateral premotor cortex (PMC). We propose that this activation can be linked to the role of the PMC in action planning – probably indicating a facilitation effect on selectional motor processes. Switching from a trained external to an unfamiliar internal focus of attention revealed enhanced activation of the left primary somatosensory cortex and intraparietal lobule. We interpret these modulations as a result of the amplifying influence of afferent information on motor processing when asked to attend internally in a motor task after being trained with an external focus.

A quantitative meta-analysis and review of motor learning in the human brain

Neuroimaging studies have improved our understanding of which brain structures are involved in motor learning. Despite this, questions remain regarding the areas that contribute consistently across paradigms with different task demands. For instance, sensorimotor tasks focus on learning novel movement kinematics and dynamics, while serial response time task (SRTT) variants focus on sequence learning. These differing task demands are likely to elicit quantifiably different patterns of neural activity on top of a potentially consistent core network. The current study identified consistent activations across 70 motor learning experiments using activation likelihood estimation (ALE) meta-analysis. A global analysis of all tasks revealed a bilateral cortical–subcortical network consistently underlying motor learning across tasks. Converging activations were revealed in the dorsal premotor cortex, supplementary motor cortex, primary motor cortex, primary somatosensory cortex, superior parietal lobule, thalamus, putamen and cerebellum. These activations were broadly consistent across task specific analyses that separated sensorimotor tasks and SRTT variants. Contrast analysis indicated that activity in the basal ganglia and cerebellum was significantly stronger for sensorimotor tasks, while activity in cortical structures and the thalamus was significantly stronger for SRTT variants. Additional conjunction analyses then indicated that the left dorsal premotor cortex was activated across all analyses considered, even when controlling for potential motor confounds. The highly consistent activation of the left dorsal premotor cortex suggests it is a critical node in the motor learning network.

Sustaining attention to simple tasks: a meta-analytic review of the neural mechanisms of vigilant attention

Maintaining attention for more than a few seconds is essential for mastering everyday life. Yet, our ability to stay focused on a particular task is limited, resulting in well-known performance decrements with increasing time on task. Intriguingly, such decrements are even more likely if the task is cognitively simple and repetitive. The attentional function that enables our prolonged engagement in intellectually unchallenging, uninteresting activities has been termed vigilant attention. Here we synthesized what we have learned from functional neuroimaging about the mechanisms of this essential mental faculty. To this end, a quantitative meta-analysis of pertinent neuroimaging studies was performed, including supplementary analyses of moderating factors. Furthermore, we reviewed the available evidence on neural time-on-task effects, additionally considering information obtained from patients with focal brain damage. Integrating the results of both meta-analysis and review, we identified a set of mainly right-lateralized brain regions that may form the core network subserving vigilant attention in humans, including dorsomedial, mid- and ventrolateral prefrontal cortex, anterior insula, parietal areas (intraparietal sulcus, temporoparietal junction), and subcortical structures (cerebellar vermis, thalamus, putamen, midbrain). We discuss the potential functional roles of different nodes of this network as well as implications of our findings for a theoretical account of vigilant attention. It is conjectured that sustaining attention is a multicomponent, nonunitary mental faculty, involving a mixture of (a) sustained/recurrent processes subserving task-set/arousal maintenance and (b) transient processes subserving the target-driven reorienting of attention. Finally, limitations of previous studies are considered and suggestions for future research are provided.

1 Hz rTMS of the left posterior parietal cortex (PPC) modifies sensorimotor timing

In order to investigate the relevance of the left posterior parietal cortex (PPC) for precise sensorimotor timing we applied 1 Hz repetitive transcranial magnetic stimulation (rTMS) over left PPC, right PPC and visual cortex of healthy participants for 10 min, respectively. The impact on sensorimotor timing of the right hand was assessed using a synchronization task that required subjects to synchronize their right index finger taps with respect to constant auditory, visual or auditory-visual pacing. Our results reveal reduced negative tap-to-pacer asynchronies following rTMS of the left PPC in all pacing conditions. This effect lasted for about 5 min after cessation of rTMS. Right PPC and visual cortex stimulation did not yield any significant behavioural effects. Since suppression of left PPC modified right-hand synchronization accuracy independent of the pacing signal's modality, the present data support the significance of left PPC for anticipatory motor control over a primary role in multisensory integration. The present data suggest that 1 Hz rTMS might interrupt a matching process of anticipated and real sensorimotor feedback within PPC. Alternatively, downregulation of left PPC activity may affect M1 excitability via functional connections leading to a delay in motor output and, thus, smaller tap-to-pacer asynchronies.

Crossmodal interactions in audiovisual emotion processing

Emotion in daily life is often expressed in a multimodal fashion. Consequently emotional information from one modality can influence processing in another. In a previous fMRI study we assessed the neural correlates of audio-visual integration and found that activity in the left amygdala is significantly attenuated when a neutral stimulus is paired with an emotional one compared to conditions where emotional stimuli were present in both channels. Here we used dynamic causal modelling to investigate the effective connectivity in the neuronal network underlying this emotion presence congruence effect. Our results provided strong evidence in favor of a model family, differing only in the interhemispheric interactions. All winning models share a connection from the bilateral fusiform gyrus (FFG) into the left amygdala and a non-linear modulatory influence of bilateral posterior superior temporal sulcus (pSTS) on these connections. This result indicates that the pSTS not only integrates multi-modal information from visual and auditory regions (as reflected in our model by significant feed-forward connections) but also gates the influence of the sensory information on the left amygdala, leading to attenuation of amygdala activity when a neutral stimulus is integrated. Moreover, we found a significant lateralization of the FFG due to stronger driving input by the stimuli (faces) into the right hemisphere, whereas such lateralization was not present for sound-driven input into the superior temporal gyrus. In summary, our data provides further evidence for a rightward lateralization of the FFG and in particular for a key role of the pSTS in the integration and gating of audio-visual emotional information.