Bilateral parietal cortex function during motor imagery

Effect of electroencephalography-based motor imagery neurofeedback on mu suppression during motor attempt in patients with stroke

OBJECTIVE

The primary aim of this study was to explore the neurophysiological effects of motor imagery neurofeedback using electroencephalography (EEG), specifically focusing on mu suppression during serial motor attempts, and to assess its potential benefits in patients with subacute stroke.

METHODS

A total of 15 patients with hemiplegia following subacute ischemic stroke were prospectively enrolled in this randomized cross-over study. This study comprised two experiments: neurofeedback and sham. Each experiment included four blocks: three blocks of resting, grasp, resting, and an interventional task, followed by one block of resting and grasp. During the resting sessions, participants fixated on a white cross on a black background for 2 min without moving their upper extremities. In the grasp sessions, participants were instructed to grasp and release their paretic hand at a frequency of about 1 Hz for 3 min while maintaining fixation on the white cross. During the interventional task, the neurofeedback presented a punching image using the affected upper limb, corresponding to the mu suppression induced by imagined movement for 3 min. In contrast, the sham presented an image based on mu suppression data from randomly selected participants. EEG data were recorded throughout the experiment, and data from electrodes C3/C4 and P3/P4 were analyzed to compare the degree of mu suppression between the neurofeedback and sham experiments.

RESULTS

Significant mu suppression was observed in the bilateral motor and parietal cortices during the neurofeedback experiment compared with the sham across serial sessions (p < 0.001). Following neurofeedback, real grasping sessions showed progressive strengthening of mu suppression in the ipsilesional motor cortex and bilateral parietal cortices compared to sessions following sham (p < 0.05). This effect was not observed in the contralesional motor cortex.

CONCLUSIONS

Motor imagery neurofeedback significantly enhances mu suppression in the ipsilesional motor and bilateral parietal cortices during motor attempts in patients with subacute stroke. These findings suggest that motor imagery neurofeedback could serve as a promising adjunctive therapy to enhance motor-related cortical activity and support motor rehabilitation in patients with stroke.

Effects of physical practice on the duration of motor imagery

Motor Simulation Theory proposes that imagined actions are produced using the brain's motor system, and should therefore always be temporally equivalent to physical movements. However, empirical results are not always consistent with this prediction. Studies indicate that the durations of unfamiliar imagined actions are over-estimated, whereas the durations of more familiar actions may be closer to (or even faster than) actual movement execution. We therefore examined the effects of different levels of practice on the durations of both physically performed and imagined actions. Participants (N=31) completed an initial assessment in which the durations of physically performed and imagined finger movement sequences were measured. Participants then completed three days of physical training in which different sequences received either extensive training (150 repetitions/session), minimal training (10 repetitions/session), or no training. In a subsequent assessment session, we found that the time taken to both physically execute and imagine performing sequences decreased with training. However, contrary to the predictions of Motor Simulation theory, imagined movement durations consistently over-estimated those of physically performed movements. While the difference in the timing of imagined and physically executed movements decreased between the initial and final assessment, this effect was not modulated by training. These results extend our understanding of the relationship between motor imagery and physical practice, and highlight a key limitation in the predictions of Motor Simulation Theory.

Motor imagery for paediatric neurorehabilitation: how much do we know? Perspectives from a systematic review

Background

Motor Imagery (MI) is a cognitive process consisting in mental simulation of body movements without executing physical actions: its clinical use has been investigated prevalently in adults with neurological disorders.

Objectives

Review of the best-available evidence on the use and efficacy of MI interventions for neurorehabilitation purposes in common and rare childhood neurological disorders.

Methods

systematic literature search conducted according to PRISMA by using the Scopus, PsycArticles, Cinahl, PUBMED, Web of Science (Clarivate), EMBASE, PsychINFO, and COCHRANE databases, with levels of evidence scored by OCEBM and PEDro Scales.

Results

Twenty-two original studies were retrieved and included for the analysis; MI was the unique or complementary rehabilitative treatment in 476 individuals (aged 5 to 18 years) with 10 different neurological conditions including, cerebral palsies, stroke, coordination disorders, intellectual disabilities, brain and/or spinal cord injuries, autism, pain syndromes, and hyperactivity. The sample size ranged from single case reports to cohorts and control groups. Treatment lasted 2 days to 6 months with 1 to 24 sessions. MI tasks were conventional, graded or ad-hoc. MI measurement tools included movement assessment batteries, mental chronometry tests, scales, and questionnaires, EEG, and EMG. Overall, the use of MI was stated as effective in 19/22, and uncertain in the remnant studies.

Conclusion

MI could be a reliable supportive/add-on (home-based) rehabilitative tool for pediatric neurorehabilitation; its clinical use, in children, is highly dependent on the complexity of MI mechanisms, which are related to the underlying neurodevelopmental disorder.

Transcranial Magnetic Stimulation of the Dorsolateral Prefrontal Cortex Increases Posterior Theta Rhythm and Reduces Latency of Motor Imagery

Experiments show activation of the left dorsolateral prefrontal cortex (DLPFC) in motor imagery (MI) tasks, but its functional role requires further investigation. Here, we address this issue by applying repetitive transcranial magnetic stimulation (rTMS) to the left DLPFC and evaluating its effect on brain activity and the latency of MI response. This is a randomized, sham-controlled EEG study. Participants were randomly assigned to receive sham (15 subjects) or real high-frequency rTMS (15 subjects). We performed EEG sensor-level, source-level, and connectivity analyses to evaluate the rTMS effects. We revealed that excitatory stimulation of the left DLPFC increases theta-band power in the right precuneus (PrecuneusR) via the functional connectivity between them. The precuneus theta-band power negatively correlates with the latency of the MI response, so the rTMS speeds up the responses in 50% of participants. We suppose that posterior theta-band power reflects attention modulation of sensory processing; therefore, high power may indicate attentive processing and cause faster responses.

Effect of the Menstrual Cycle on Electroencephalogram Alpha and Beta Bands During Motor Imagery and Action Observation

Female sex steroids (FSS) can affect the motor system, modulating motor cortex excitability as well as performance in dexterity and coordination tasks. However, it has not yet been explored whether FSS affects the cognitive components of motor behavior. Mu is a sensorimotor rhythm observed by electroencephalography (EEG) in alpha (8–12 Hz) and beta (15–30 Hz) frequency bands in practices such as motor imagery (MI) and action observation (AO). This rhythm represents a window for studying the activity of neural circuits involved in motor cognition. Herein we investigated whether the alpha-mu and beta-mu power in the sensorimotor region (C3 and C4, hypothesis-driven approach) and the alpha and beta power over frontal, parietal, and occipital regions (data-driven approach) are modulated differently in the menstrual, follicular, and luteal phases of menstrual cycles in right-handed dominant women. To do so, these women underwent MI and AO in the three menstrual cycle phases. The spectral activity of the cortical regions for the alpha and beta bands were compared between phases of the menstrual cycle and a correlation analysis was also performed in relation to estrogen and progesterone levels. For the hypothesis-based approach, beta-mu event-related desynchronization (ERD) was significantly stronger in the C3 channel in the follicular phase than in the menstrual and luteal phases. For the data-driven approach, beta ERD during MI was higher in the follicular phase than in the menstrual and luteal phases in the frontal region. These findings suggest the effect of FSS on executive movement control. No effect of menstrual cycle phases was observed in cortical areas investigated during OA, but alpha and beta bands correlated positively with the follicular phase plasma estradiol level. Thus, the attenuation of alpha and beta bands referring to mirror neuron activities appears to be associated with inhibition of cortical activity when estradiol levels are lower, improving cognitive processing of motor action.

See, Hear, or Feel - to Speak: A Versatile Multiple-Choice Functional Near-Infrared Spectroscopy-Brain-Computer Interface Feasible With Visual, Auditory, or Tactile Instructions

Severely motor-disabled patients, such as those suffering from the so-called "locked-in" syndrome, cannot communicate naturally. They may benefit from brain-computer interfaces (BCIs) exploiting brain signals for communication and therewith circumventing the muscular system. One BCI technique that has gained attention recently is functional near-infrared spectroscopy (fNIRS). Typically, fNIRS-based BCIs allow for brain-based communication via voluntarily modulation of brain activity through mental task performance guided by visual or auditory instructions. While the development of fNIRS-BCIs has made great progress, the reliability of fNIRS-BCIs across time and environments has rarely been assessed. In the present fNIRS-BCI study, we tested six healthy participants across three consecutive days using a straightforward four-choice fNIRS-BCI communication paradigm that allows answer encoding based on instructions using various sensory modalities. To encode an answer, participants performed a motor imagery task (mental drawing) in one out of four time periods. Answer encoding was guided by either the visual, auditory, or tactile sensory modality. Two participants were tested outside the laboratory in a cafeteria. Answers were decoded from the time course of the most-informative fNIRS channel-by-chromophore combination. Across the three testing days, we obtained mean single- and multi-trial (joint analysis of four consecutive trials) accuracies of 62.5 and 85.19%, respectively. Obtained multi-trial accuracies were 86.11% for visual, 80.56% for auditory, and 88.89% for tactile sensory encoding. The two participants that used the fNIRS-BCI in a cafeteria obtained the best single- (72.22 and 77.78%) and multi-trial accuracies (100 and 94.44%). Communication was reliable over the three recording sessions with multi-trial accuracies of 86.11% on day 1, 86.11% on day 2, and 83.33% on day 3. To gauge the trade-off between number of optodes and decoding accuracy, averaging across two and three promising fNIRS channels was compared to the one-channel approach. Multi-trial accuracy increased from 85.19% (one-channel approach) to 91.67% (two-/three-channel approach). In sum, the presented fNIRS-BCI yielded robust decoding results using three alternative sensory encoding modalities. Further, fNIRS-BCI communication was stable over the course of three consecutive days, even in a natural (social) environment. Therewith, the developed fNIRS-BCI demonstrated high flexibility, reliability and robustness, crucial requirements for future clinical applicability.

Effect of Motor Imagery Training on Motor Learning in Children and Adolescents: A Systematic Review and Meta-Analysis

Background: There is an urgent need to systematically analyze the growing body of literature on the effect of motor imagery (MI) training in children and adolescents. Methods: Seven databases and clinicaltrials.gov were searched. Two reviewers independently screened references and full texts, and extracted data (studies’ methodology, MI elements, temporal parameters). Two studies were meta-analyzed providing the standard mean difference (SDM). Selected studies were evaluated with the risk of bias (RoB) and GRADE tools. Results: A total of 7238 references were retrieved. The sample size of the 22 included studies, published between 1995 and 2021, ranged from 18 to 136 participants, totaling 934 (nine to 18 years). Studies included healthy pupils, mentally retarded adolescents, children with motor coordination difficulties or with mild mental disabilities. The motor learning tasks focused on upper, lower and whole body movements. SMDs for the primary outcome of pooled studies varied between 0.83 to 1.87 (95% CI, I², T² varied 0.33–3.10; p = 0.001; 0–74%; 0–0.59). RoB varied between some concerns and high risk. GRADE rating was low. Conclusions: MI combined with physical practice (PP) might have a high potential for healthy and impaired children and adolescents. However, important reporting recommendations (PETTLEP, TIDieR, CONSORT) should be followed. The systematic review was registered with PROSPERO: CRD42021237361.

Knowing how to do it or doing it? A double dissociation between tool-gesture production and tool-gesture knowledge

Deciding how to manipulate an object to fulfill a goal requires accessing different types of object-related information. How these different types of information are integrated and represented in the brain is still an open question. Here, we focus on examining two types of object-related information-tool-gesture knowledge (i.e., how to manipulate an object), and tool-gesture production (i.e., the actual manipulation of an object). We show a double dissociation between tool-gesture knowledge and tool-gesture production: Patient FP presents problems in pantomiming tool use in the context of a spared ability to perform judgments about an object's manipulation, whereas Patient LS can pantomime tool use, but is impaired at performing manipulation judgments. Moreover, we compared the location of the lesions in FP and LS with those sustained by two classic ideomotor apraxic patients (IMA), using a cortical thickness approach. Patient FP presented lesions in common with our classic IMA that included the left inferior parietal lobule (IPL), and specifically the supramarginal gyrus, the left parietal operculum, the left premotor cortex and the left inferior frontal gyrus, whereas Patient LS and our classic IMA patients presented common lesions in regions of the superior parietal lobule (SPL), motor areas (as primary somatosensory cortex, premotor cortex and primary motor cortex), and frontal areas. Our results show that tool-gesture production and tool-gesture knowledge can be behaviorally and neurally doubly dissociated and put strong constraints on extant theories of action and object recognition and use.

Dancing in Your Head: An Interdisciplinary Review

The aim of this review is to highlight the most relevant contributions on dance in neuroscientific research. Neuroscience has analyzed the mirror system through neuroimaging techniques, testing its role in imitative learning, in the recognition of other people's emotions and especially in the understanding of the motor behavior of others. This review analyses the literature related to five general areas: (I) breakthrough studies on the mirror system, and subsequent studies on its involvement in the prediction, the execution, the control of movement, and in the process of "embodied simulation" within the intersubjective relationship; (II) research focused on investigating the neural networks in action observation, and the neural correlates of motor expertise highlighted by comparative studies on different dance styles; (III) studies dealing with the viewer's experience of dance according to specific dance repertoires, which revealed the relevance of choreographic choices for aesthetic appreciation; (IV) studies focused on dance as an aesthetic experience, where both the emotional and the cultural dimension play a significant role, and whose investigation paves the way to further progress both in empirical and in phenomenological research methodologies; (V) collaboration-based experiments, in which neuroscientists and choreographers developed expertise-related questions, especially focusing on the multiple phenomena that underlie motor imagery.

Event-related potential (P300): the effects of levetiracetam in cognitive performance

BACKGROUND

The current study is a reanalysis in the time domain of EEG data collection in healthy adults during an oddball paradigm using levetiracetam (LEV) vs. placebo acute administration. Specifically, the event-related potential (ERP) technique provides a tool for exploring the EEG responses to a specific event/stimulus. One of the ERP components widely studied is the P300 component, which is associated with the last stage of information processing and a general measurement of "cognitive efficiency."

METHODS

The sample was composed of thirteen healthy right-handed individuals randomized to participate under two conditions: LEV and placebo. Electrophysiological measures were collected before and after drug intake. We explored the oddball paradigm, which is commonly used with healthy individuals to investigate the stages of information processing.

RESULTS

The electrophysiological results showed a main effect of condition on P300 amplitude for the frontal (F3, Fz, F4), central (C3, Cz, C4), and parietal electrodes (P3, Pz, P4). The post hoc comparisons (Scheffé's test) demonstrated the significant differences between electrodes. Regarding P300 latency, all regions represented a main effect of condition. A P300 latency reduction was observed during LEV condition compared with placebo.

CONCLUSION

Our study observed the ERP component-P300-through the variation of its amplitude and latency to evaluate a supposed higher CNS efficiency when participants were under the LEV effect. Our findings sustain this premise, mainly due to reducing in P300 latency for the LEV condition, supporting the neural efficiency hypothesis.

Probing the temporal dynamics of movement inhibition in motor imagery

Beyond the lack of overt movement in motor imagery (MI), MI is thought to be functionally equivalent to motor execution (ME). Two theories appear viable to explain the neural mechanism underlying the inhibition of movement in MI, with one suggesting the inhibition of movement in MI occurs early in the planning process, and the other suggesting it occurs after the planning for movement is compete. Here we sought to generate evidence related to the timing of movement inhibition in MI. Participants performed a motor task via MI and ME that had distinct preparation and performance phases, with brain activity obtained throughout. Analysis of sensor-level data was performed to isolate event related desynchrony (ERD) in the mu and beta frequency bands in both a sensorimotor and left parietal region of interest (ROI). The magnitude of ERD in the sensorimotor ROI was significantly greater in ME than MI during both the preparatory and performance phases. The reduced ERD in the mu and beta frequency bands in the sensorimotor ROI during the preparatory phase for MI, compared to ME, suggests that movement planning is inhibited (or at least reduced) in MI, contributing to the lack of movement. While past work has shown that the networks of functional brain activity underlying MI and ME are heavily overlapping, differences in the temporal dynamics of this activity suggest that MI and ME are not equivalent processes.

Motor imagery training: Kinesthetic imagery strategy and inferior parietal fMRI activation

Motor imagery (MI) is the mental simulation of action frequently used by professionals in different fields. However, with respect to performance, well-controlled functional imaging studies on MI training are sparse. We investigated changes in fMRI representation going along with performance changes of a finger sequence (error and velocity) after MI training in 48 healthy young volunteers. Before training, we tested the vividness of kinesthetic and visual imagery. During tests, participants were instructed to move or to imagine moving the fingers of the right hand in a specific order. During MI training, participants repeatedly imagined the sequence for 15 min. Imaging analysis was performed using a full-factorial design to assess brain changes due to imagery training. We also used regression analyses to identify those who profited from training (performance outcome and gain) with initial imagery scores (vividness) and fMRI activation magnitude during MI at pre-test (MI_pre ). After training, error rate decreased and velocity increased. We combined both parameters into a common performance index. FMRI activation in the left inferior parietal lobe (IPL) was associated with MI and increased over time. In addition, fMRI activation in the right IPL during MI_pre was associated with high initial kinesthetic vividness. High kinesthetic imagery vividness predicted a high performance after training. In contrast, occipital activation, associated with visual imagery strategies, showed a negative predictive value for performance. Our data echo the importance of high kinesthetic vividness for MI training outcome and consider IPL as a key area during MI and through MI training.

Specific Brain Lesions Impair Explicit Motor Imagery Ability: A Systematic Review of the Evidence

OBJECTIVE

To determine which neurologic disorders/lesions impair or restrict motor imagery (MI) ability.

DATA SOURCES

CINAHL, Cochrane, Embase, MEDLINE, Web of Science, PsychINFO, Physiotherapy Evidence Database, and Grey Literature were searched between May 8 and May 14, 2014. Keywords and Medical Subject Headings from 2 concepts (MI and lesion) were exploded to include related search terms (eg, mental practice/mental imagery, neurologic damage/lesion).

STUDY SELECTION

Two independent reviewers assessed the 3861 studies that resulted from the database search. The studies were assessed for relevancy using the following inclusion criteria: use of explicit kinesthetic MI; neurologic lesion location identified; and use of an MI ability assessment tool.

DATA EXTRACTION

Twenty-three studies encompassing 196 participants were included. The 23 studies used 8 different methods for assessing MI ability. MI assessment scores were then normalized to facilitate comparison across studies.

DATA SYNTHESIS

Lesion locations comprised many brain areas, including cortical (eg, parietal and frontal lobes), subcortical (eg, basal ganglia, thalamus), and cerebellum. Lesion etiology primarily was comprised of stroke and Parkinson disease. Several participants presented with lesions resulting from other pathologies. Subjects with parietal lobe damage were most impaired on their ability to perform MI. Subjects with frontal lobe and basal ganglia damage also consistently showed impairment in MI ability.

CONCLUSIONS

Subjects with damage to specific brain structures, including the parietal and frontal lobes, showed impaired MI ability. As such, MI-based neurorehabilitation may not be efficacious in all patient populations. Therefore, decisions related to the use of MI in neurorehabilitation should, in part, be based on the patient's underlying pathophysiology.

Neural evidence for the use of digit-image mnemonic in a superior memorist: an fMRI study

Some superior memorists demonstrated exceptional memory for reciting a large body of information. The underlying neural correlates, however, are seldom addressed. C.L., the current holder of Guinness World Record for reciting 67,890 digits in π, participated in this functional magnetic resonance imaging (fMRI) study. Thirteen participants without any mnemonics training were included as controls. Our previous studies suggested that C.L. used a digit-image mnemonic in studying and recalling lists of digits, namely associating 2-digit groups of “00” to “99” with images and generating vivid stories out of them (Hu et al., 2009). Thus, 2-digit condition was included, with 1-digit numbers and letters as control conditions. We hypothesized that 2-digit condition in C.L. should elicit the strongest activity in the brain regions which are associated with his mnemonic. Functional MRI results revealed that bilateral frontal poles (FPs, BA10), left superior parietal lobule (SPL), left premotor cortex (PMC), and left dorsolateral prefrontal cortex (DLPFC), were more engaged in both the study and recall phase of 2-digit condition for C.L. relative to controls. Moreover, the left middle/inferior frontal gyri (M/IFG) and intraparietal sulci (IPS) were less engaged in the study phase of 2-digit condition for C.L. (vs. controls). These results suggested that C.L. relied more on brain regions that are associated with episodic memory other than verbal rehearsal while he used his mnemonic strategies. This study supported theoretical accounts of restructured cognitive mechanisms for the acquisition of superior memory performance.

Motor imagery is less efficient in adults with probable developmental coordination disorder: evidence from the hand rotation task

The present study aimed to provide preliminary insight into the integrity of motor imagery (MI) in adults with probable developmental coordination disorder (pDCD). Based on a strong body of evidence indicating that paediatric samples of DCD often experience difficulties engaging MI, we hypothesised that young adults with pDCD would demonstrate similar difficulties. The performance of 12 young adults (19-35 years) with pDCD was compared to 47 age-matched controls on a traditional mental hand rotation task. Mean inverse efficiency scores were generated for each participant by dividing each participant's mean RT by their proportion of correct responses at each of the stimuli presentation conditions. Preliminary analysis revealed that the performance profiles of individuals with pDCD and age-matched controls showed evidence of being constrained by the biomechanical and postural constraints of real movement, suggesting that both groups engaged in an embodied (MI) strategy to complete the task. Despite engaging in a MI strategy, however, young adults with pDCD were nonetheless significantly less efficient when doing so, shown by significant main effects for group on all group efficiency comparisons. Based on the assumption that MI provides insight into the internal 'neural' action representation that precedes action, we argue that the less efficient MI performance demonstrated by young adults with pDCD may indicate inefficiencies engaging or implementing internal action representations. Implications and directions for future research are discussed.

Alpha band functional connectivity correlates with the performance of brain-machine interfaces to decode real and imagined movements

Brain signals recorded from the primary motor cortex (M1) are known to serve a significant role in coding the information brain–machine interfaces (BMIs) need to perform real and imagined movements, and also to form several functional networks with motor association areas. However, whether functional networks between M1 and other brain regions, such as these motor association areas, are related to the performance of BMIs is unclear. To examine the relationship between functional connectivity and performance of BMIs, we analyzed the correlation coefficient between performance of neural decoding and functional connectivity over the whole brain using magnetoencephalography. Ten healthy participants were instructed to execute or imagine three simple right upper limb movements. To decode the movement type, we extracted 40 virtual channels in the left M1 via the beam forming approach, and used them as a decoding feature. In addition, seed-based functional connectivities of activities in the alpha band during real and imagined movements were calculated using imaginary coherence. Seed voxels were set as the same virtual channels in M1. After calculating the imaginary coherence in individuals, the correlation coefficient between decoding accuracy and strength of imaginary coherence was calculated over the whole brain. The significant correlations were distributed mainly to motor association areas for both real and imagined movements. These regions largely overlapped with brain regions that had significant connectivity to M1. Our results suggest that use of the strength of functional connectivity between M1 and motor association areas has the potential to improve the performance of BMIs to perform real and imagined movements.

Drawing lines while imagining circles: Neural basis of the bimanual coupling effect during motor execution and motor imagery

When people simultaneously draw lines with one hand and circles with the other hand, both trajectories tend to assume an oval shape, showing that hand motor programs interact (the so-called "bimanual coupling effect"). The aim of the present study was to investigate how motor parameters (drawing trajectories) and the related brain activity vary during bimanual movements both in real execution and in motor imagery tasks. In the 'Real' modality, subjects performed right hand movements (lines) and, simultaneously, Congruent (lines) or Non-congruent (circles) left hand movements. In the 'Imagery' modality, subjects performed only right hand movements (lines) and, simultaneously, imagined Congruent (lines) or Non-congruent (circles) left hand movements. Behavioral results showed a similar interference of both the real and the imagined circles on the actually executed lines, suggesting that the coupling effect also pertains to motor imagery. Neuroimaging results showed that a prefrontal-parietal network, mostly involving the pre-Supplementary Motor Area (pre-SMA) and the posterior parietal cortex (PPC), was significantly more active in Non-congruent than in Congruent conditions, irrespective of task (Real or Imagery). The data also confirmed specific roles of the right superior parietal lobe (SPL) in mediating spatial interference, and of the left PPC in motor imagery. Collectively, these findings suggest that real and imagined Non-congruent movements activate common circuits related to the intentional and predictive operation generating bimanual coupling, in which the pre-SMA and the PPC play a crucial role.

Association between dual task-related decrease in walking speed and real versus imagined Timed Up and Go test performance

BACKGROUND AND AIMS

To examine whether older people with markedly dual task-related decreases in walking speed - a marker of disturbed higher-level gait control and falls - have a larger discrepancy between real and imagined Timed Up and Go (TUG) test times than those with less dual task-related decreases in walking speed.

METHODS

Based on a prospective cross-sectional study, 193 older adults (mean age 77.4 ± 5.9 years; 44.0 % women) referred to and consecutively assessed at a Swiss university clinic for a gait analysis to assess either gait disorders, fall risk or memory disorders were included. For all participants, walking speed was measured using a GAITRite(®) electronic walkway system during usual walking at self-selected pace and while dual tasking (i.e., usual walking and simultaneously counting backwards out loud). In addition, real Timed Up and Go (TUGr) and imagined Timed Up and Go (TUGi) (i.e., the time needed to imagine performing the TUGr) times were measured with a stopwatch. Differences between both walking conditions for walking speed (delta of walking speed) and both TUG conditions (delta of TUG time) were calculated. Age, gender, height, total number drugs taken per day, daily use of psychoactive drugs, use of walking aid, history of falls, Mini-Mental State Examination score, near vision and education level were used as covariables in this analysis.

RESULTS

Participants were categorized into two groups based on being in the lowest tertian (i.e., <33 %: group A corresponding to participants undisturbed by dual task) or not (i.e., ≥33 %: group B corresponding to participants disturbed by dual task) of the delta of walking speed. In both groups, TUGr and TUGi times were similar (P = .169 and P = .839). In both groups, TUGi was faster than TUGr (P < .001). Delta of TUG time was significantly greater in group B compared to group A (P < .001). After adjustment for all covariables, only the delta of walking speed was significantly associated with the delta of TUG time (P = <.001). Stepwise backward regression showed that polypharmacy (P = .017) and delta of walking speed (P = <.001) were associated with an increase in delta of TUG time, whereas an increased MMSE score (P = .030) was associated with a decrease in delta of TUG time.

CONCLUSION

These findings show that a large discrepancy between real and imagined TUG performances is significantly correlated with a decrease in walking speed while dual tasking, and thus may also be a surrogate marker of disturbed higher-level gait control. The quickly and easily performed TUG tests may represent a feasible, practical screening tool for early detection of higher-level gait disorders in older adults.

The neurobiology of imagination: possible role of interaction-dominant dynamics and default mode network

This work aims at presenting some hypotheses about the potential neurobiological substrate of imagery and imagination. For the present purposes, we will define imagery as the production of mental images associated with previous percepts, and imagination as the faculty of forming mental images of a novel character relating to something that has never been actually experienced by the subject but at a great extent emerges from his inner world. The two processes appear intimately related and imagery can arguably be considered as one of the main components of imagination. In this proposal, we argue that exaptation and redeployment, two basic concepts capturing important aspects of the evolution of biological structures and functions (Anderson, 2007), could also be useful in explaining imagery and imagination. As far as imagery is concerned it is proposed that neural structures originally implicated in performing certain functions, e.g., motor actions, can be reused for the imagery of the virtual execution of that function. As far as imagination is concerned we speculate that it can be the result of a “tinkering” that combines and modifies stored perceptual information and concepts leading to the creation of novel “mental objects” that are shaped by the subject peculiar inner world. Hence it is related to his self-awareness. The neurobiological substrate of the tinkering process could be found in a hierarchical model of the brain characterized by a multiplicity of functional modules (FMs) that can be assembled according to different spatial and temporal scales. Thus, it is surmised that a possible mechanism for the emergence of imagination could be represented by modulatory mechanisms controlling the perviousness of “modifiers” along the communication channels within and between FMs leading to their dynamically reassembling into novel configurations.

Two assessments to evaluate imagery ability: translation, test-retest reliability and concurrent validity of the German KVIQ and Imaprax

Background

A combination of physical practice and motor imagery (MI) can improve motor function. It is essential to assess MI vividness in patients with sensorimotor impairments before implementing MI interventions. The study's aims were to translate the Canadian Kinaesthetic and Visual Imagery Questionnaire (KVIQ) and the French Imaprax, and to examine reliability and validity of the German versions.

Methods

Questionnaires were translated according to guidelines. With examiner’s help patients (diagnosis: stroke: subacute/chronic, brain tumour, Multiple Sclerosis, Parkinson’s disease) were tested twice within seven days (T0, T1). KVIQ-G: Patients were shown a movement by the examiner, before executing and imagining the movement. They rated vividness of the image and intensity of the sensations on a five-point Likert-scale. Imaprax required a 3-step procedure: imagination of one of six gestures; evaluation of gesture understanding, vividness, and imagery perspective. Questionnaire data were analysed overall and for each group. Reliability parameters were calculated: intraclass correlation coefficient (ICC), Cronbach's alpha, standard error of measurement, minimal detectable change. Validity parameters included Spearman's rank correlation coefficient and factor analysis of the KVIQ-G-20.

Results

Patients (N = 73, 28 females, age: 63 ± 13) showed the following at T0: KVIQ-G-20_vis 41.7 ± 9, KVIQ-G-10_vis 21.1 ± 5. ICC for KVIQ-G-20_vis and KVIQ-G-10_vis was 0.77; KVIQ-G-20_kin 36.4 ± 12, KVIQ-G-10_kin 18.3 ± 6. ICCs for KVIQ-G-20_kin and KVIQ-G-10_kin were 0.83/0.85; Imaprax_vis 32.7 ± 4 and ICC 0.51. Internal consistency was estimated for KVIQ-G-20 α_vis = 0.94/α_kin = 0.92, KVIQ-G-10 α_vis = 0.88/α_kin = 0.96, Imaprax-G α_vis = 0.70. Validity testing was performed with 19 of 73 patients, who chose an internal perspective: r_s = 0.36 (p = 0.13). Factor analysis revealed two factors correlating with r = 0.36. Both explain 69.7% of total variance.

Conclusions

KVIQ-G and Imaprax-G are reliable instruments to assess MI in patients with sensorimotor impairments confirmed by a KVIQ-G-factor analysis. KVIQ-G visual values were higher than kinaesthetic values. Patients with Multiple Sclerosis showed the lowest, subacute stroke patients the highest values. Hemiparetic patients scored lower in both KVIQ-G subscales on affected side compared to non-affected side. It is suggested to administer the Imaprax-G before the KVIQ-G to test patient’s ability to distinguish between external and internal MI perspective. Duration of both questionnaires lead to an educational effect. Imaprax validity testing should be repeated.

Neural activation and functional connectivity during motor imagery of bimanual everyday actions

Bimanual actions impose intermanual coordination demands not present during unimanual actions. We investigated the functional neuroanatomical correlates of these coordination demands in motor imagery (MI) of everyday actions using functional magnetic resonance imaging (fMRI). For this, 17 participants imagined unimanual actions with the left and right hand as well as bimanual actions while undergoing fMRI. A univariate fMRI analysis showed no reliable cortical activations specific to bimanual MI, indicating that intermanual coordination demands in MI are not associated with increased neural processing. A functional connectivity analysis based on psychophysiological interactions (PPI), however, revealed marked increases in connectivity between parietal and premotor areas within and between hemispheres. We conclude that in MI of everyday actions intermanual coordination demands are primarily met by changes in connectivity between areas and only moderately, if at all, by changes in the amount of neural activity. These results are the first characterization of the neuroanatomical correlates of bimanual coordination demands in MI. Our findings support the assumed equivalence of overt and imagined actions and highlight the differences between uni- and bimanual actions. The findings extent our understanding of the motor system and may aid the development of clinical neurorehabilitation approaches based on mental practice.

Task-dependent interaction between parietal and contralateral primary motor cortex during explicit versus implicit motor imagery

Both mental rotation (MR) and motor imagery (MI) involve an internalization of movement within motor and parietal cortex. Transcranial magnetic stimulation (TMS) techniques allow for a task-dependent investigation of the interhemispheric interaction between these areas. We used image-guided dual-coil TMS to investigate interactions between right inferior parietal lobe (rIPL) and left primary motor cortex (M1) in 11 healthy participants. They performed MI (right index-thumb pinching in time with a 1 Hz metronome) or hand MR tasks, while motor evoked potentials (MEPs) were recorded from right first dorsal interosseous. At rest, rIPL conditioning 6 ms prior to M1 stimulation facilitated MEPs in all participants, whereas this facilitation was abolished during MR. While rIPL conditioning 12 ms prior to M1 stimulation had no effect on MEPs at rest, it suppressed corticomotor excitability during MI. These results support the idea that rIPL forms part of a distinct inhibitory network that may prevent unwanted movement during imagery tasks.

Parallel alterations of functional connectivity during execution and imagination after motor imagery learning

BACKGROUND

Neural substrates underlying motor learning have been widely investigated with neuroimaging technologies. Investigations have illustrated the critical regions of motor learning and further revealed parallel alterations of functional activation during imagination and execution after learning. However, little is known about the functional connectivity associated with motor learning, especially motor imagery learning, although benefits from functional connectivity analysis attract more attention to the related explorations. We explored whether motor imagery (MI) and motor execution (ME) shared parallel alterations of functional connectivity after MI learning.

METHODOLOGY/PRINCIPAL FINDINGS

Graph theory analysis, which is widely used in functional connectivity exploration, was performed on the functional magnetic resonance imaging (fMRI) data of MI and ME tasks before and after 14 days of consecutive MI learning. The control group had no learning. Two measures, connectivity degree and interregional connectivity, were calculated and further assessed at a statistical level. Two interesting results were obtained: (1) The connectivity degree of the right posterior parietal lobe decreased in both MI and ME tasks after MI learning in the experimental group; (2) The parallel alterations of interregional connectivity related to the right posterior parietal lobe occurred in the supplementary motor area for both tasks.

CONCLUSIONS/SIGNIFICANCE

These computational results may provide the following insights: (1) The establishment of motor schema through MI learning may induce the significant decrease of connectivity degree in the posterior parietal lobe; (2) The decreased interregional connectivity between the supplementary motor area and the right posterior parietal lobe in post-test implicates the dissociation between motor learning and task performing. These findings and explanations further revealed the neural substrates underpinning MI learning and supported that the potential value of MI learning in motor function rehabilitation and motor skill learning deserves more attention and further investigation.

Neuronal correlates to consciousness. The "Hall of Mirrors" metaphor describing consciousness as an epiphenomenon of multiple dynamic mosaics of cortical functional modules

Humans share the common intuition of a self that has access to an inner 'theater of mind' (Baars, 2003). The problem is how this internal theater is formed. Moving from Cook's view (Cook, 2008), we propose that the 'sentience' present in single excitable cells is integrated into units of neurons and glial cells transiently assembled into "functional modules" (FMs) organized as systems of encased networks (from cell networks to molecular networks). In line with Hebb's proposal of 'cell assemblies', FMs can be linked to form higher-order mosaics by means of reverberating circuits. Brain-level subjective awareness results from the binding phenomenon that coordinates several FM mosaics. Thus, consciousness may be thought as the global result of integrative processes taking place at different levels of miniaturization in plastic mosaics. On the basis of these neurobiological data and speculations and of the evidence of 'mirror neurons' the 'Hall of Mirrors' is proposed as a significant metaphor of consciousness. This article is part of a Special Issue entitled: Brain Integration.

Cortico-Cortical Connectivity between Right Parietal and Bilateral Primary Motor Cortices during Imagined and Observed Actions: A Combined TMS/tDCS Study

Previous transcranial magnetic stimulation (TMS) studies showed functional connections between the parietal cortex (PC) and the primary motor cortex (M1) during tasks of different reaching-to-grasp movements. Here, we tested whether the same network is involved in cognitive processes such as imagined or observed actions. Single pulse TMS of the right and left M1 during rest and during a motor imagery and an action observation task (i.e., an index-thumb pinch grip in both cases) was used to measure corticospinal excitability changes before and after conditioning of the right PC by 10 min of cathodal, anodal, or sham transcranial direct current stimulation (tDCS). Corticospinal excitability was indexed by the size of motor-evoked potentials (MEPs) from the contralateral first dorsal interosseous (FDI; target) and abductor digiti minimi muscle (control) muscles. Results showed selective ipsilateral effects on the M1 excitability, exclusively for motor imagery processes: anodal tDCS enhanced the MEPs' size from the FDI muscle, whereas cathodal tDCS decreased it. Only cathodal tDCS impacted corticospinal facilitation induced by action observation. Sham stimulation was always uneffective. These results suggest that motor imagery, differently from action observation, is sustained by a strictly ipsilateral parieto-motor cortex circuits. Results might have implication for neuromodulatory rehabilitative purposes.