Motor facilitation during action observation: a magnetic stimulation study

Focusing: A new challenger for improving the empathy skills of medical students

OBJECTIVES

Studies of empathy among medical students reported an alarming significant decline during medical education. Some authors identified the third year of education as the most problematic one: empathy decreased significantly when the curriculum was shifting to patient-care activities. Scientists have tried to address the means and methods for improving empathy skills (e.g., by improving communication abilities), but investigations on this topic are missing. Based on the Damasio's hypothesis and scientific studies, we assume that Focusing (i.e., an embodied practice where one attends to a bodily felt sense and uses it to understand the self and situations) would be significantly and positively linked to empathy.

METHOD

After their clinical internships, we selected third-year medical students (N = 121) and asked them to complete three questionnaires assessing empathy, Focusing, and social desirability.

RESULTS

By controlling social desirability, findings confirmed that Focusing (especially the "having access to the felt body" component) was significantly and positively linked with empathy (i.e., Fantasy & Perspective-Taking), and positively predicted Fantasy, Perspective-Taking, and Empathic Concern.

CONCLUSIONS

These preliminary results suggest that the felt body plays a role in increasing empathy (mainly on cognitive empathy). Few scientific studies have described constructs that significantly promote cognitive empathy and empathic concern (a deeply anchored trait of empathy), which suggests new avenues of investigation.

Hypnosis-induced modulation of corticospinal excitability during motor imagery

Hypnosis can be considered an altered state of consciousness in which individuals produce movements under suggestion without apparent voluntary control. Despite its application in contexts implying motor control, evidence for the neurophysiological mechanisms underlying hypnosis is scarce. Inter-individual differences in hypnotic susceptibility suggest that sensorimotor strategies may manifest in a hypnotic state. We tested by means of transcranial magnetic stimulation applied over the primary motor cortex whether motor system activation during a motor imagery task differs in the awake and in the hypnotic state. To capture individual differences, 30 healthy volunteers were classified as high or low hypnotizable (Highs and Lows) according to ad-hoc validated scales measuring hypnotic susceptibility and personality questionnaires. Corticospinal activation during motor imagery in the hypnotic state was greater in the Highs than the Lows. Intrinsic motivation in task performance and level of persuasion modulated corticospinal activation in the Highs. Corticospinal system activation under hypnosis may have practical implications that merit research in areas where hypnosis can be applied to improve motor performance, such as loss of motor abilities and sports.

Proactive gaze is present during biological and non-biological motion observation

Others' action observation activates in the observer a coordinated hand-eye motor program, covert for the hand (i.e. motor resonance), and overt for the eye (i.e. proactive gaze), similar to that of the observed agent. The biological motion hypothesis of action anticipation claims that proactive gaze occurs only in the presence of biological motion, and that kinematic information is sufficient to determine the anticipation process. The results of the present study did not support the biological motion hypothesis of action anticipation. Specifically, proactive gaze was present during observation of both a biological accelerated-decelerated motion and a non-biological constant velocity motion (Experiment 1), in the presence of a barrier able to restrict differences between the two kinematics to the motion profile of individual markers prior to contact (Experiment 2), but only if an object was present at the end point of the movement trajectory (Experiment 3). Furthermore, proactive gaze was found independently of the presence of end effects temporally congruent with the instant in which the movement stopped (Experiments 4, and 5). We propose that the involvement of the observer's motor system is not restricted to when the agent moves with natural kinematics, and it is mandatory whenever the presence of an agent or a goal is evident, regardless of physical appearance, natural kinematics, and the possibility to identify the action behind the stimulus.

Do Gaze Behaviours during Action Observation Predict Interpersonal Motor Resonance?

Interpersonal motor resonance (IMR) is a common putative index of the mirror neuron system (MNS), a network containing specialised cells that fire during both action execution and observation. Visual content inputs to the MNS, however, it is unclear whether visual behaviours mediate the putative MNS response. We aimed to examine gaze effects on IMR during action observation. Neurotypical adults (N = 99; 60 female) underwent transcranial magnetic stimulation, electromyography, and eye-tracking during the observation of videos of actors performing grasping actions. IMR was measured as a percentage change in motor evoked potentials (MEPs) of the first dorsal interosseous muscle during action observation relative to baseline. MEP facilitation was observed during action observation, indicating IMR (65.43%, SE = 11.26%, P < 0.001). Fixations occurring in biologically relevant areas (face/hand/arm) yielded significantly stronger IMR (81.03%, SE = 14.15%) than non-biological areas (63.92%, SE = 14.60, P = 0.012). This effect, however, was only evident in the first of four experimental blocks. Our results suggest that gaze fixation can modulate IMR, but this may be affected by the salience and novelty of the observed action. These findings have important methodological implications for future studies in both clinical and healthy populations.

Non-invasive stimulation in the social brain: the methodological challenges

Use of non-invasive brain stimulation methods (NIBS) has become a common approach to study social processing in addition to behavioural, imaging and lesion studies. However, research using NIBS to investigate social processing faces challenges. Overcoming these is important to allow valid and reliable interpretation of findings in neurotypical cohorts, but also to allow us to tailor NIBS protocols to atypical groups with social difficulties. In this review, we consider the utility of brain stimulation as a technique to study and modulate social processing. We also discuss challenges that face researchers using NIBS to study social processing in neurotypical adults with a view to highlighting potential solutions. Finally, we discuss additional challenges that face researchers using NIBS to study and modulate social processing in atypical groups. These are important to consider given that NIBS protocols are rarely tailored to atypical groups before use. Instead, many rely on protocols designed for neurotypical adults despite differences in brain function that are likely to impact response to NIBS.

Activation of cerebellum and basal ganglia during the observation and execution of manipulative actions

Studies on action observation mostly described the activation of a network of cortical areas, while less investigation focused specifically on the activation and role of subcortical nodes. In the present fMRI study, we investigated the recruitment of cerebellum and basal ganglia during the execution and observation of object manipulation performed with the right hand. The observation conditions consisted in: (a) observation of manipulative actions; (b) observation of sequences of random finger movements. In the execution conditions, participants had to perform the same actions or movements as in (a) and (b), respectively. The results of conjunction analysis showed significant shared activations during both observation and execution of manipulation in several subcortical structures, including: (1) cerebellar lobules V, VI, crus I, VIIIa and VIIIb (bilaterally); (2) globus pallidus, bilaterally, and left subthalamic nucleus; (3) red nucleus (bilaterally) and left thalamus. These findings support the hypothesis that the action observation/execution network also involves subcortical structures, such as cerebellum and basal ganglia, forming an integrated network. This suggests possible mechanisms, involving these subcortical structures, underlying learning of new motor skills, through action observation and imitation.

Soundbeam imitation intervention: Training children with autism to imitate meaningless body gestures through music

Purpose

This paper aims to present the application and critical reflection on the effects of a intervention for children with autism spectrum disorder (ASD): the Soundbeam Imitation Intervention (SII). The intervention is based on the imitation of meaningless body gestures supported by a musical feedback. The rationale underlying SII is that mirror neurons deficit may represent the cause for the incomplete development of social and motor functioning in children with ASD. Following this assumption, it is possible to hypothesise that a systematic activation of this a system through the simultaneous observation-execution of meaningless body gestures may affect functional changes of mirror-related functions.

Design/methodology/approach

A sample of 14 children, who were between 5 and 9 years of age, with a diagnosis of ASD were involved in a six weeks’ SII programme. The programme is designed as a three-step progression, where each step includes exercises that focus on an activity: synchronous/one arm imitation, synchronous/two arms imitation and delayed imitation. Exercises are based on repeated movements-melodies associations of increasing difficulty. Motor imitation and social attention were assessed using a synchronous video-modelling task pre and post intervention.

Findings

Data highlight significant improvements in imitation accuracy and duration of social sustained attention were achieved.

Originality/value

Data reported in this paper provide preliminary and promising evidence that imitation and social attention skills acquired through SII can be generalised to a video-modelling imitation setting. The SII ordinal execution has included meaningless gestures, usually excluded from previous interventions, and this adds further validity to the training.

Representing Multiple Observed Actions in the Motor System

There is now converging evidence that others' actions are represented in the motor system. However, social cognition requires us to represent not only the actions but also the interactions of others. To do so, it is imperative that the motor system can represent multiple observed actions. The current fMRI study investigated whether this is possible by measuring brain activity from 29 participants while they observed 2 right hands performing sign language gestures. Three key results were obtained. First, brain activity in the premotor and parietal motor cortex was stronger when 2 hands performed 2 different gestures than when 1 hand performed a single gesture. Second, both individual observed gestures could be decoded from brain activity in the same 2 regions. Third, observing 2 different gestures compared with 2 identical gestures activated brain areas related to motor conflict, and this activity was correlated with parietal motor activity. Together, these results show that the motor system is able to represent multiple observed actions, and as such reveal a potential mechanism by which third-party social encounters could be processed in the brain.

Continuing to look in the mirror: A review of neuroscientific evidence for the broken mirror hypothesis, EP-M model and STORM model of autism spectrum conditions

The mirror neuron system has been argued to be a key brain system responsible for action understanding and imitation. Subsequently, mirror neuron system dysfunction has therefore been proposed to explain the social deficits manifested within autism spectrum condition, an approach referred to as the broken mirror hypothesis. Despite excitement surrounding this hypothesis, extensive research has produced insufficient evidence to support the broken mirror hypothesis in its pure form, and instead two alternative models have been formulated: EP-M model and the social top-down response modulation (STORM) model. All models suggest some dysfunction regarding the mirror neuron system in autism spectrum condition, be that within the mirror neuron system itself or systems that regulate the mirror neuron system. This literature review compares these three models in regard to recent neuroscientific investigations. This review concludes that there is insufficient support for the broken mirror hypothesis, but converging evidence supports an integrated EP-M and STORM model.

Visibly constraining an agent modulates observers' automatic false-belief tracking

Our motor system can generate representations which carry information about the goals of another agent’s actions. However, it is not known whether motor representations play a deeper role in social understanding, and, in particular, whether they enable tracking others’ beliefs. Here we show that, for adult observers, reliably manifesting an ability to track another’s false belief critically depends on representing the agent’s potential actions motorically. One signature of motor representations is that they can be disrupted by constraints on an observed agent’s action capacities. We therefore used a ‘mummification’ technique to manipulate whether the agent in a visual ball-detection task was free to act or whether he was visibly constrained from acting. Adults’ reaction times reliably reflected the agent’s beliefs only when the agent was free to act on the ball and not when the agent was visibly constrained from acting. Furthermore, it was the agent’s constrained action capabilities, rather than any perceptual novelty, that determined whether adult observers’ reaction times reliably reflected the agent’s beliefs. These findings signal that our motor system may underpin more of social cognition than previously imagined, and, in particular, that motor representations may underpin automatic false-belief tracking.

Brain correlates of motor complexity during observed and executed actions

Recently, cortical areas with motor properties have attracted attention widely to their involvement in both action generation and perception. Inferior frontal gyrus (IFG), ventral premotor cortex (PMv) and inferior parietal lobule (IPL), presumably consisting of motor-related areas, are of particular interest, given that they respond to motor behaviors both when they are performed and observed. Converging neuroimaging evidence has shown the functional roles of IFG, PMv and IPL in action understanding. Most studies have focused on the effects of modulations in goals and kinematics of observed actions on the brain response, but little research has explored the effects of manipulations in motor complexity. To address this, we used fNIRS to examine the brain activity in the frontal, motor, parietal and occipital regions, aiming to better understand the brain correlates involved in encoding motor complexity. Twenty-one healthy adults executed and observed two hand actions that differed in motor complexity. We found that motor complexity sensitive brain regions were present in the pars opercularis IFG/PMv, primary motor cortex (M1), IPL/supramarginal gyrus and middle occipital gyrus (MOG) during action execution, and in pars opercularis IFG/PMv and M1 during action observation. Our findings suggest that the processing of motor complexity involves not only M1 but also pars opercularis IFG, PMv and IPL, each of which plays a critical role in action perception and execution.

Human Mirror Neuron System Based Alarms in the Cockpit: A Neuroergonomic Evaluation

Controlled Flight Into Terrain (CFIT) events still remain among the deadliest accidents in aviation. When facing the possible occurrence of such an event, pilots have to immediately react to the ground proximity alarm ("Pull Up" alarm) in order to avoid the impending collision. However, the pilots' reaction to this alarm is not always optimal. This may be at least partly due to the low visual saliency of the current alarm and the deleterious effects of stress that alleviate the pilot's reactions. In the present study, two experiments (in a laboratory and in a flight simulator) were conducted to (1) investigate whether hand gesture videos (a hand pulling back the sidestick) can trigger brainwave frequencies related to the mirror neuron system; (2) determine whether enhancing the visual characteristics of the "Pull Up" alarm could improve pilots' response times. Electrophysiological results suggest that hand gesture videos attracted more participants' attention (greater alpha desynchronization in the parieto-occipital area) and possibly triggered greater activity of the mirror neuron system (greater mu and beta desynchronizations at central electrodes). Results obtained in the flight simulator revealed that enhancing the visual characteristics of the original "Pull Up" alarm improved the pilots' reaction times. However, no significant difference in reaction times between an enlarged "Pull Up" inscription and the hand gesture video was found. Further work is needed to determine whether mirror neuron system based alarms could bring benefits for flight safety, in particular, these alarms should be assessed during a high stress context.

Motor imagery enhances corticospinal transmission mediated by cervical premotoneurons in humans

Imaging movement has positive effects on the reacquisition of motor functions after damage to the central nervous system. This study shows that motor imagery facilitates oligosynaptic corticospinal excitation that is mediated via cervical premotoneurons, which may be important for motor recovery in monkeys and humans. Current findings highlight how this imagery might be a beneficial tool for movement disorders through effects on premotoneuron circuitry.

Effects of Music Reading on Motor Cortex Excitability in Pianists: A Transcranial Magnetic Stimulation Study

Neurophysiological studies suggest that music reading facilitates sensorimotor cortex. The aim of this study was to evaluate (1) whether in pianists, reading notes in bass and treble clef selectively enhances right and left primary motor cortex (M1) excitability; and (2) whether reading notes played with the thumb or little finger selectively modulates the excitability of specific muscles. Twenty musicians (11 pianists, 9 non-pianists) participated. Transcranial magnetic stimulation (TMS) was applied while subjects read the bass or the treble clef of sheets music and during the observation of a blank staff (baseline). When pianists read the treble clef, the excitability of the left M1 was higher compared to that recorded in the right M1. Moreover, in the treble clef condition motor evoked potentials (MEPs) induced by TMS of the left M1 were higher when pianists read notes to be played with the 5° finger (little finger) with respect to 1° finger (thumb) notes, whereas in the bass clef condition TMS of the right M1 induced higher MEPs for 1° finger note compared to 5° finger notes. No significant modulation was observed in non-pianists. These data support the view that music reading may induce specific inter- and intra-hemispheric modulation of the motor cortex excitability.

Temporal fluctuations in the brain's modular architecture during movie-watching

Brain networks are flexible and reconfigure over time to support ongoing cognitive processes. However, tracking statistically meaningful reconfigurations across time has proven difficult. This has to do largely with issues related to sampling variability, making instantaneous estimation of network organization difficult, along with increased reliance on task-free (cognitively unconstrained) experimental paradigms, limiting the ability to interpret the origin of changes in network structure over time. Here, we address these challenges using time-varying network analysis in conjunction with a naturalistic viewing paradigm. Specifically, we developed a measure of inter-subject network similarity and used this measure as a coincidence filter to identify synchronous fluctuations in network organization across individuals. Applied to movie-watching data, we found that periods of high inter-subject similarity coincided with reductions in network modularity and increased connectivity between cognitive systems. In contrast, low inter-subject similarity was associated with increased system segregation and more rest-like architectures. We then used a data-driven approach to uncover clusters of functional connections that follow similar trajectories over time and are more strongly correlated during movie-watching than at rest. Finally, we show that synchronous fluctuations in network architecture over time can be linked to a subset of features in the movie. Our findings link dynamic fluctuations in network integration and segregation to patterns of inter-subject similarity, and suggest that moment-to-moment fluctuations in functional connectivity reflect shared cognitive processing across individuals.

Spatial frequency tuning of motor responses reveals differential contribution of dorsal and ventral systems to action comprehension

Understanding object-directed actions performed by others is central to everyday life. This ability is thought to rely on the interaction between the dorsal action observation network (AON) and a ventral object recognition pathway. On this view, the AON would encode action kinematics, and the ventral pathway, the most likely intention afforded by the objects. However, experimental evidence supporting this model is still scarce. Here, we aimed to disentangle the contribution of dorsal vs. ventral pathways to action comprehension by exploiting their differential tuning to low-spatial frequencies (LSFs) and high-spatial frequencies (HSFs). We filtered naturalistic action images to contain only LSF or HSF and measured behavioral performance and corticospinal excitability (CSE) using transcranial magnetic stimulation (TMS). Actions were embedded in congruent or incongruent scenarios as defined by the compatibility between grips and intentions afforded by the contextual objects. Behaviorally, participants were better at discriminating congruent actions in intact than LSF images. This effect was reversed for incongruent actions, with better performance for LSF than intact and HSF. These modulations were mirrored at the neurophysiological level, with greater CSE facilitation for congruent than incongruent actions for HSF and the opposite pattern for LSF images. Finally, only for LSF did we observe CSE modulations according to grip kinematics. While results point to differential dorsal (LSF) and ventral (HSF) contributions to action comprehension for grip and context encoding, respectively, the negative congruency effect for LSF images suggests that object processing may influence action perception not only through ventral-to-dorsal connections, but also through a dorsal-to-dorsal route involved in predictive processing.

Enhancing mirror visual feedback with intermittent theta burst stimulation in healthy adults

BACKGROUND

Excitatory brain stimulation, in the form of intermittent theta burst stimulation (iTBS), combined with mirror visual feedback (MVF), is hypothesized to promote neuroplasticity and motor performance.

OBJECTIVE

This study aimed to investigate the combined effects of iTBS with mirror training (MT) on the MVF-induced sensorimotor event-related desynchronization (ERD) and the non-dominant hand motor performance in healthy adults.

METHODS

Eighteen healthy right-handed subjects were randomly assigned to one of three groups (Group 1: iTBS plus MT, Group 2: iTBS plus sham MT, or Group 3: sham iTBS plus MT). For participants in Groups 1 and 3, motor training was performed for 15 minutes for the right hand over four consecutive days, with MVF superimposing on their inactive left hand behind a mirror. Participants in Group 2 received the same right-hand motor training, but the mirror was covered without MVF. iTBS or sham iTBS was applied daily over the right primary motor cortex prior to the training. Electroencephalography at pre/post-training was recorded while participants performed right-hand movement under mirror and direct view. Motor performance was assessed at baseline and post-training.

RESULTS

Baseline comparisons demonstrated that a shift in sensorimotor ERD towards the right hemisphere was induced by MVF, in mu-1 (8-10 Hz) (p = 0.002), mu-2 (10-12 Hz) (p = 0.004) and beta-1 (12-16 Hz) (p = 0.049) bands. After the training, participants in Group 1 showed a stronger MVF-induced sensorimotor ERD in mu-1 (p = 0.017) and mu-2 (p = 0.009) bands than those in Group 3. No significant between-group difference in motor outcomes was observed.

CONCLUSIONS

iTBS appears to prime subjects' brain to be more receptive to MVF.

A study of EEG mu neurofeedback during action observation

The mirror system is a brain network that gets activated during action performance and observation. Brain mu waves have been used as a mirror system activity index; however, mu rhythm is prone to contamination by occipital alpha wave activity, thus raising a concern regarding its reliability as an index of the mirror system activity. In this study, we investigated whether mu suppression can be used as an index of neurofeedback training, which influences mirror system activities. Participants observed videos of hand movement under three different conditions: central mu feedback (muFB), occipital alpha feedback (aFB), and simple observation without any feedback (OBS). Results showed that at the 4-5 min mark, mu wave was most significantly suppressed in the central site at muFB. We thus demonstrated the possibility of increasing mu wave suppression in feedback training using a specific stimulus such as motion observation.

Sensorimotor Expectations Bias Motor Resonance during Observation of Object Lifting: The Causal Role of pSTS

Transcranial magnetic stimulation studies have highlighted that corticospinal excitability is increased during observation of object lifting, an effect termed "motor resonance." This facilitation is driven by movement features indicative of object weight, such as object size or observed movement kinematics. Here, we investigated in 35 humans (23 females) how motor resonance is altered when the observer's weight expectations, based on visual information, do not match the actual object weight as revealed by the observed movement kinematics. Our results highlight that motor resonance is not robustly driven by object weight but easily masked by a suppressive mechanism reflecting the correctness of weight expectations. Subsequently, we investigated in 24 humans (14 females) whether this suppressive mechanism was driven by higher-order cortical areas. For this, we induced "virtual lesions" to either the posterior superior temporal sulcus (pSTS) or dorsolateral prefrontal cortex (DLPFC) before having participants perform the task. Importantly, virtual lesion of pSTS eradicated this suppressive mechanism and restored object weight-driven motor resonance. In addition, DLPFC virtual lesion eradicated any modulation of motor resonance. This indicates that motor resonance is heavily mediated by top-down inputs from both pSTS and DLPFC. Together, these findings shed new light on the theorized cortical network driving motor resonance. That is, our findings highlight that motor resonance is not only driven by the putative human mirror neuron network consisting of the primary motor and premotor cortices as well as the anterior intraparietal sulcus, but also by top-down input from pSTS and DLPFC.SIGNIFICANCE STATEMENT Observation of object lifting activates the observer's motor system in a weight-specific fashion: Corticospinal excitability is larger when observing lifts of heavy objects compared with light ones. Interestingly, here we demonstrate that this weight-driven modulation of corticospinal excitability is easily suppressed by the observer's expectations about object weight and that this suppression is mediated by the posterior superior temporal sulcus. Thus, our findings show that modulation of corticospinal excitability during observed object lifting is not robust but easily altered by top-down cognitive processes. Finally, our results also indicate how cortical inputs, originating remotely from motor pathways and processing action observation, overlap with bottom-up motor resonance effects.

Muscle-specific modulation of indirect inputs to primary motor cortex during action observation

Single-pulse transcranial magnetic stimulation (spTMS) studies report that movement observation facilitates corticospinal excitability in primary motor cortex (M1) in a muscle-specific manner. However, motor evoked potentials (MEPs) elicited by spTMS are known to reflect the summation of several descending volleys in corticospinal neurons which are evoked via mono- and polysynaptic inputs (so-called indirect waves or I-waves). It is unclear which of these components contribute to the muscle-specific modulation of M1 during action observation. The interactions between different I-waves are reflected in the facilitatory peaks elicited with a short-intracortical facilitation (SICF) protocol when two pulses are sent to M1 at precise intervals (i.e., 1.3, 2.5 or 4.1 ms). Here, we explored the modulation of early and late SICF peaks during action observation by measuring highly specific MEP amplitude changes measured in two muscles (index, FDI and little finger, ADM) while participants observed two different actions (precision and whole-hand grip). Our results demonstrate that both early (1.3 ms) and late (2.5 and 4.1 ms) SICF peaks are modulated in the context of movement observation. However, only the second peak (ISI 2.5 ms) was significantly associated with the muscle-specific modulation of corticospinal excitability as measured with spTMS. This late SICF peak is believed to reflect the activity cortico-cortical pathways involved in the facilitation of muscle-specific representations in M1. Thus, our findings suggest that movement observation leads to widespread activation of different neural circuits within M1, including those mediating cortico-cortical communication.

Eye contact enhances interpersonal motor resonance: comparing video stimuli to a live two-person action context

Previous research has shown a link between eye contact and interpersonal motor resonance, indicating that the mirroring of observed movements is enhanced when accompanied with mutual eye contact between actor and observer. Here, we further explored the role of eye contact within a naturalistic two-person action context. Twenty-two participants observed simple hand movements combined with direct or averted gaze presented via a live model in a two-person setting or via video recordings, while transcranial magnetic stimulation was applied over the primary motor cortex (M1) to measure changes in M1 excitability. Skin conductance responses and gaze behavior were also measured to investigate the role of arousal and visual attention herein. Eye contact significantly enhanced excitability of the observer's M1 during movement observation within a two-person setting. Notably, participants with higher social responsiveness (Social Communication subscale of the Social Responsiveness Scale) displayed a more pronounced modulation of M1 excitability by eye gaze. Gaze-related modulations in M1 excitability were, however, not associated with differences in visual attention or autonomic arousal. In summary, the current study highlights the effectiveness and feasibility of adopting paradigms with high ecological validity for studying the modulation of mirror system processes by subtle social cues, such as eye gaze.

The Effects of Instruction Manipulation on Motor Performance Following Action Observation

The effects of action observation (AO) on motor performance can be modulated by instruction. The effects of two top-down aspects of the instruction on motor performance have not been fully resolved: those related to attention to the observed task and the incorporation of motor imagery (MI) during AO. In addition, the immediate vs. 24-h retention test effects of those instruction’s aspects are yet to be elucidated. Forty-eight healthy subjects were randomly instructed to: (1) observe reaching movement (RM) sequences toward five lighted units with the intention of reproducing the same sequence as fast and as accurate as possible (Intentional + Attentional group; AO+At); (2) observe the RMs sequence with the intention of reproducing the same sequence as fast and as accurate as possible and simultaneously to the observation to imagine performing the RMs (Intentional + attentional + MI group; AO+At+MI); and (3) observe the RMs sequence (Passive AO group). Subjects’ performance was tested before and immediately after the AO and retested after 24 h. During each of the pretest, posttest, and retest, the subject performed RMs toward the units that were activated in the same order as the observed sequence. Occasionally, the sequence order was changed by beginning the sequence with a different activated unit. The outcome measures were: averaged response time of the RMs during the sequences, difference between the response time of the unexpected and expected RMs and percent of failures to reach the target within 1 s. The averaged response time and the difference between the response time of the unexpected and expected RMs were improved in all groups at posttest compared to pretest, regardless of instruction. Averaged response time was improved in the retest compared to the posttest only in the Passive AO group. The percent of failures across groups was higher in pretest compared to retest. Our findings suggest that manipulating top-down aspects of instruction by adding attention and MI to AO in an RM sequence task does not improve subsequent performance more than passive observation. Off-line learning of the sequence in the retention test was improved in comparison to posttest following passive observation only.

The Role of Primary Motor Cortex: More Than Movement Execution

The predominant role of the primary motor cortex (M1) in motor execution is well acknowledged. However, additional roles of M1 are getting evident in humans owing to advances in noninvasive brain stimulation (NIBS) techniques. This review collates such studies in humans and proposes that M1 also plays a key role in higher cognitive processes. The review commences with the studies that have investigated the nature of connectivity of M1 with other cortical regions in light of studies based on NIBS. The review then moves on to discuss the studies that have demonstrated the role of M1 in higher cognitive processes such as attention, motor learning, motor consolidation, movement inhibition, somatomotor response, and movement imagery. Overall, the purpose of the review is to highlight the additional role of M1 in motor cognition besides motor control, which remains unexplored.

Susceptibility to the fusion illusion is modulated during both action execution and action observation

Many researchers have proposed that when an individual observes the actions of another individual, the observer simulates the action using many of the same neural areas that are involved in action production. The present study was designed to test this simulation hypothesis by comparing the perception of multisensory stimuli during both the execution and observation of an aiming action. The present work used the fusion illusion - an audio-visual illusion in which two visual stimuli presented with one auditory stimulus are erroneously perceived as being one visual stimulus. Previous research has shown that, during action execution, susceptibly to this illusion is reduced early in the execution of the movement when visual information may be more highly weighted than other sensory information. We sought to determine whether or not a non-acting observer of an action showed a similar reduction in susceptibility to the fusion illusion. Participants fixated a target and either executed or observed a manual aiming movement to that target. Audiovisual stimuli were presented at 0, 100, or 200 ms relative to movement onset and participants reported the number of perceived flashes after the movement was completed. Analysis of perceived flashes revealed that participants were less susceptible to the fusion illusion when the stimuli were presented early (100 ms) relative to later in the movement (200 ms). Critically, this pattern emerged in both execution and observation tasks. These findings support the hypothesis that observers simulate the performance of the actor and experience comparable real-time alterations in multisensory processing.

The interactive effect of empathy and motor cortex stimulation on hand gesture comprehension

Previous research has demonstrated that the Action-Observation Network (AON) is involved in both emotional-embodiment (empathy) and action-embodiment mechanisms. In the current study, we hypothesized that interfering with the AON will impair action recognition and that this impairment will be modulated by empathy levels. Fifty-two participants conducted a semantic decision task of hand gesture recognition, while we interfered with the AON by applying active (n = 26) or sham (n = 26) transcranial Direct Current Stimulation (tDCS) to the hand area of the primary motor cortex. We found that interfering with the AON impaired the performance of participants with high empathy levels and enhanced the performance of participants with low empathy. This finding suggests that the embodiment module may be flexible, and that it can be enhanced in individuals with low empathy by simple manipulation of motor activation.

The last chance to pass the ball: investigating the role of temporal expectation and motor resonance in processing temporal errors in motor actions

Humans can acquire information on others' motor outputs (action prediction) and intentions (action understanding) according to their individual motor repertoire and to the detected gesture's features (e.g. temporal patterns). We aimed at dissociating between action prediction and action understanding abilities in soccer players and novices observing soccer action videos including correct timing pass (CTP) or delayed pass (DP). First, we used an occluding paradigm to evaluate participants' ability to predict the correct time to pass the ball. Although soccer players showed reduced reaction times, all subjects showed a similar pattern of performance: during DP observation, responses appeared delayed with respect to the other conditions but anticipated with respect to the observed DP. In a separate experiment, we investigated the ability to recognize CTP vs DP and the modulation of primary motor cortex (M1) excitability associated to video observation. Only soccer players showed selective modulation of M1 according to the plausibility of the observed action, with increased excitability during the observation of the CTP and in a phase preceding the DP. In conclusion, action prediction ability seems to be independent from the individual motor repertoire. By contrast, only subjects with previously acquired sensorimotor skills are able to infer the observed action's long-term intention.

Motor activation is modulated by visual experience during cyclic gait observation: A transcranial magnetic stimulation study

Transcranial magnetic stimulation (TMS) has been widely utilized to noninvasively explore the motor system during the observation of human movement. However, few studies have characterized motor cortex activity during periodic gait observation. Thus, this study examined the effects of an observer's visual experience and/or intention to imitate on corticospinal excitability during the observation of another's gait. Twenty-six healthy volunteers were included in this study and allocated to two different groups. Participants in the visual experience group had formal experience with gait observation (physical therapist training), while those in the control group did not. Motor-evoked potentials induced by TMS in the tibialis anterior and soleus muscles were measured as surrogates of corticospinal excitability. Participants were seated and, while resting, they observed a demonstrator's gait or observed it with the intention to subsequently reproduce it. Compared with the resting state, cyclic gait observation led to significant corticospinal facilitation in the tibialis anterior and soleus muscles. However, this pattern of corticospinal facilitation in the measured muscles was not coupled to the pattern of crural muscle activity during actual gait and was independent of the step cycle. This motor cortex facilitation effect during gait observation was enhanced by the observer's visual experience in a manner that was not step cycle-dependent, while the observer's intent to imitate did not affect corticospinal excitatory input to either muscle. In addition, visual experience did not modulate corticospinal excitability in gait-related crural muscles. Our findings indicate that motor cortex activity during gait observation is not in line with the timing of muscle activity during gait execution and is modulated by an individual's gait observation experience. These results suggest that visual experience acquired from repetitive gait observation may facilitate the motor system's control on bipedal walking, but may not promote the learning of muscle activity patterns.

Design and validation of two embodied mirroring setups for interactive games with autistic children using the NAO humanoid robot

Socially assistive robots have shown potential benefits in therapy of child and elderly patients with social and cognitive deficits. In particular, for autistic children, humanoid robots could enhance engagement and attention, thanks to their simplified toy-like appearance and the reduced set of possible movements and expressions. The recent focus on autism-related motor impairments has increased the interest on developing new robotic tools aimed at improving not only the social capabilities but also the motor skills of autistic children. To this purpose, we have designed two embodied mirroring setups using the NAO humanoid robot. Two different tracking systems were used and compared: Inertial Measurement Units and the Microsoft Kinect, a marker-less vision based system. Both platforms were able to mirror upper limb basic movements of two healthy subjects, an adult and a child. However, despite the lower accuracy, the Kinect-based setup was chosen as the best candidate for embodied mirroring in autism treatment, thanks to the lower intrusiveness and reduced setup time. A prototype of an interactive mirroring game was developed and successfully tested with the Kinect-based platform, paving the way to the development of a versatile and powerful tool for clinical use with autistic children.

Action processing in the motor system: Transcranial Magnetic Stimulation (TMS) evidence of shared mechanisms in the visual and linguistic modalities

In two experiments, we compared the dynamics of corticospinal excitability when processing visually or linguistically presented tool-oriented hand actions in native speakers and sequential bilinguals. In a third experiment we used the same procedure to test non-motor, low-level stimuli, i.e. scrambled images and pseudo-words. Stimuli were presented in sequence: pictures (tool + tool-oriented hand action or their scrambled counterpart) and words (tool noun + tool-action verb or pseudo-words). Experiment 1 presented German linguistic stimuli to native speakers, while Experiment 2 presented English stimuli to non-natives. Experiment 3 tested Italian native speakers. Single-pulse trascranial magnetic stimulation (spTMS) was applied to the left motor cortex at five different timings: baseline, 200 ms after tool/noun onset, 150, 350 and 500 ms after hand/verb onset with motor-evoked potentials (MEPs) recorded from the first dorsal interosseous (FDI) and abductor digiti minimi (ADM) muscles. We report strong similarities in the dynamics of corticospinal excitability across the visual and linguistic modalities. MEPs' suppression started as early as 150 ms and lasted for the duration of stimulus presentation (500 ms). Moreover, we show that this modulation is absent for stimuli with no motor content. Overall, our study supports the notion of a core, overarching system of action semantics shared by different modalities.

Principles of Neurorehabilitation After Stroke Based on Motor Learning and Brain Plasticity Mechanisms

What are the principles underlying effective neurorehabilitation? The aim of neurorehabilitation is to exploit interventions based on human and animal studies about learning and adaptation, as well as to show that the activation of experience-dependent neuronal plasticity augments functional recovery after stroke. Instead of teaching compensatory strategies that do not reduce impairment but allow the patient to return home as soon as possible, functional recovery might be more sustainable as it ensures a long-term reduction in impairment and an improvement in quality of life. At the same time, neurorehabilitation permits the scientific community to collect valuable data, which allows inferring about the principles of brain organization. Hence neuroscience sheds light on the mechanisms of learning new functions or relearning lost ones. However, current rehabilitation methods lack the exact operationalization of evidence gained from skill learning literature, leading to an urgent need to bridge motor learning theory and present clinical work in order to identify a set of ingredients and practical applications that could guide future interventions. This work aims to unify the neuroscientific literature relevant to the recovery process and rehabilitation practice in order to provide a synthesis of the principles that constitute an effective neurorehabilitation approach. Previous attempts to achieve this goal either focused on a subset of principles or did not link clinical application to the principles of motor learning and recovery. We identified 15 principles of motor learning based on existing literature: massed practice, spaced practice, dosage, task-specific practice, goal-oriented practice, variable practice, increasing difficulty, multisensory stimulation, rhythmic cueing, explicit feedback/knowledge of results, implicit feedback/knowledge of performance, modulate effector selection, action observation/embodied practice, motor imagery, and social interaction. We comment on trials that successfully implemented these principles and report evidence from experiments with healthy individuals as well as clinical work.

Using Action-congruent Language Facilitates the Motor Response during Action Observation: A Combined Transcranial Magnetic Stimulation and Eye-tracking Study

There is evidence that action observation (AO) and the processing of action-related words are associated with increased activity in cortical motor regions. Research has examined the effects of AO and action verb processing on activity in the motor system independently. The aim of this experiment was to investigate, for the first time, the modulation of corticospinal excitability and visual attention during the concurrent processing of action verbs and AO stimuli. Twenty participants took part in an integrated transcranial magnetic stimulation and eye-tracking protocol. Single-pulse transcranial magnetic stimulation was delivered to the hand representation of the left motor cortex during (i) observation of a static hand, (ii) AO of a hand squeezing a sponge, (iii) AO of the same action with an audio recording of the word "squeeze," and (iv) AO of the same action with an audio recording of the word "green". Motor evoked potentials were recorded from the abductor pollicis brevis and abductor digiti minimi muscles of the right hand. Eye gaze was recorded throughout the four conditions as a proxy for visual attention. Interviews were conducted to discuss participants' preferences and imagery use for each condition. The AO and action verb condition resulted in significantly increased motor evoked potential amplitudes in the abductor pollicis brevis muscle; participants also made significantly more fixations on the sponge and reported wanting to move their hand more in the action verb condition. The inclusion of auditory action verbs, alongside AO stimuli, in movement simulation interventions could have implications for the delivery of AO interventions for motor (re)learning.

Social Cognition in Gilles de la Tourette Syndrome

Abstract. Research on the neural mechanisms underlying Gilles de la Tourette syndrome (GTS) has mostly concentrated on abnormalities in basal ganglia circuits. Recent alternative accounts, however, focused more on social and affective aspects. Individuals with GTS show peculiarities in their social and affective domain, including echophenomena, coprolalia, and nonobscene socially inappropriate behavior. This article reviews the experimental and theoretical work done on the social symptoms of GTS. We discuss the role of different social cognitive and affective functions and associated brain networks, namely, the social-decision-making system, theory-of-mind functions, and the so-called “mirror-neuron” system. Although GTS affects social interactions in many ways, and although the syndrome includes aberrant social behavior, the underlying cognitive, affective, and neural processes remain to be investigated.

Muscle-Specific Modulation of Spinal Reflexes in Lower-Limb Muscles during Action Observation with and without Motor Imagery of Walking

Action observation (AO) and motor imagery (MI) are useful techniques in neurorehabilitation. Previous studies have reported that AO and MI facilitate corticospinal excitability only in those muscles that are active when actually performing the observed or imagined movements. However, it remained unclear whether spinal reflexes modulate multiple muscles simultaneously. The present study focused on AO and MI of walking and aimed to clarify their effects on spinal reflexes in lower-limb muscles that are recruited during actual walking. Ten healthy males participated in the present study. Spinal reflex parameters evoked by transcutaneous spinal cord stimulation were measured from five lower-limb muscles during rest, AO, and AO combined with MI (AO + MI) conditions. Our results showed that spinal reflexes were increased in the tibialis anterior and biceps femoris muscles during AO and in the tibialis anterior, soleus, and medial gastrocnemius muscles during AO + MI, compared with resting condition. Spinal reflex parameters in the vastus medialis muscle were unchanged. These results indicate the muscle-specific modulations of spinal reflexes during AO and AO + MI. These findings reveal the underlying neural activities induced by AO, MI, and their combined processes.

Brain activation induced by different strengths of hand grasp: a functional magnetic resonance imaging study

Mirror neuron system can be activated by observation and execution of an action. It has an important function of action understanding. We investigated brain activations in humans by observing the strength of a hand grasp using functional magnetic resonance imaging. Twenty right-handed healthy individuals, consisting of 10 males and 10 females, aged 22.40 ± 2.04 years, were recruited into this study from September to November 2017 via posters. Light hand grasp task video showed a hand lightly grasping and releasing a ball repeatedly. Powerful hand grasp task video showed a hand tightly grasping and releasing a ball repeatedly. Functional magnetic resonance imaging block design paradigm comprised five stimulation blocks alternating with five baseline blocks. Stimulation blocks were presented with two stimulus tasks, consisting of a light grasp and a powerful grasp. Region of interest was defined around the inferior parietal lobule, inferior frontal gyrus, and superior temporal sulcus which have been called mirror neuron system. The inferior parietal lobule, fusiform, postcentral, occipital, temporal, and frontal gyri were activated during light and powerful grasp tasks. The BOLD signal response of a powerful grasp was stronger than that of a light grasp. These results suggest that brain activation of the inferior parietal lobule, which is the core brain region of the mirror neuron system, was stronger in the powerful grasp task than in the light grasp task. We believe that our results might be helpful for instructing rehabilitation of brain injury. This study was approved by the Institutional Review Board of Daegu Oriental Hospital of Daegu Haany University on September 8, 2017 (approval No. DHUMC-D-17020-PRO-01).

Two-day-old newborns learn to discriminate accelerated-decelerated biological kinematics from constant velocity motion

Already in uterus the hand moves with the typical accelerated-decelerated kinematics of goal-directed actions and, from the twenty-second week of pregnancy, the unborn shows the ability to modulate the velocity of the movement depending on the nature of the target. According to the direct matching hypothesis, this motor knowledge may be sufficient to attune neonates' motion perception-like adults'-to biological kinematics. Using dots configuration motions which varied with respect to the kinematics of goal-directed actions, we observed that two-day-old human newborns did not show any spontaneous preference for either biological accelerated-decelerated motion or non-biological constant velocity motion when these were simultaneously presented in a standard preferential looking paradigm. In contrast, newborns preferred the biological kinematics after the repeated visual presentation of the different motions in a standard infant-control visual habituation paradigm. We propose that present results indicate that the relationship between perception and action does not require only action development but also the accumulation of sufficient perceptual experience. They also suggest a fast plasticity of the sensorimotor system in linking an already acquired motor knowledge with a newly experienced congruent visual stimulation.

Dynamic task observation: A gaze-mediated complement to traditional action observation treatment?

Action observation elicits changes in primary motor cortex known as motor resonance, a phenomenon thought to underpin several functions, including our ability to understand and imitate others' actions. Motor resonance is modulated not only by the observer's motor expertise, but also their gaze behaviour. The aim of the present study was to investigate motor resonance and eye movements during observation of a dynamic goal-directed action, relative to an everyday one - a reach-grasp-lift (RGL) action, commonly used in action-observation-based neurorehabilitation protocols. Skilled and novice golfers watched videos of a golf swing and an RGL action as we recorded MEPs from three forearm muscles; gaze behaviour was concurrently monitored. Corticospinal excitability increased during golf swing observation, but it was not modulated by expertise, relative to baseline; no such changes were observed for the RGL task. MEP amplitudes were related to participants' gaze behaviour: in the RGL condition, target viewing was associated with lower MEP amplitudes; in the golf condition, MEP amplitudes were positively correlated with time spent looking at the effector or neighbouring regions. Viewing of a dynamic action such as the golf swing may enhance action observation treatment, especially when concurrent physical practice is not possible.

To Watch is to Work: a Review of NeuroImaging Data on Tool Use Observation Network

Since the discovery of mirror neurons in the 1990s, many neuroimaging studies have tackled the issue of action observation with the aim of unravelling a putative homolog human system. However, these studies do not distinguish between non-tool-use versus tool-use actions, implying that a common brain network is systematically involved in the observation of any action. Here we provide evidence for a brain network dedicated to tool-use action observation, called the tool-use observation network, mostly situated in the left hemisphere, and distinct from the non-tool-use action observation network. Areas specific for tool-use action observation are the left cytoarchitectonic area PF within the left inferior parietal lobe and the left inferior frontal gyrus. The neural correlates associated with the observation of tool-use reported here offer new insights into the neurocognitive bases of action observation and tool use, as well as addressing more fundamental issues on the origins of specifically human phenomena such as cumulative technological evolution.

Observation of Both Skilled and Erroneous Object Lifting Can Improve Predictive Force Scaling in the Observer

Recent studies have highlighted that the observation of hand-object interactions can influence perceptual weight judgments made by an observer. Moreover, observing salient motor errors during object lifting allows individuals to update their internal sensorimotor representation about object weight. Embodying observed visuomotor cues for the planning of a motor command further enables individuals to accurately scale their fingertip forces when subsequently lifting the same object. However, it is still unknown whether the observation of a skilled lift is equally able to mediate predictive motor control in the observer. Here, we tested this hypothesis by asking participants to grasp and lift a manipulandum after observing an actor's lift. The object weight changed unpredictably (light or heavy) every fourth to sixth trial performed by the actor. Participants were informed that they would always lift the same weight as the actor and that, based on the experimental condition, they would have to observe skilled or erroneously performed lifts. Our results revealed that the observation of both skilled and erroneously performed lifts allows participants to update their internal sensorimotor object representation, in turn enabling them to predict force scaling accurately. These findings suggest that the observation of salient motor errors, as well as subtle features of skilled motor performance, are embodied in the observer's motor repertoire and can drive changes in predictive motor control.

Low or High-Level Motor Coding? The Role of Stimulus Complexity

Transcranial magnetic stimulation (TMS) studies have shown that observing an action induces activity in the onlooker's motor system. In light of the muscle specificity and time-locked mirroring nature of the effect, this motor resonance has been traditionally viewed as an inner automatic replica of the observed movement. Notably, studies highlighting this aspect have classically considered movement in isolation (i.e., using non-realistic stimuli such as snapshots of hands detached from background). However, a few recent studies accounting for the role of contextual cues, motivational states, and social factors, have challenged this view by showing that motor resonance is not completely impervious to top-down modulations. A debate is still present. We reasoned that motor resonance reflects the inner replica of the observed movement only when its modulation is assessed during the observation of movements in isolation. Conversely, the presence of top-down modulations of motor resonance emerges when other high-level factors (i.e., contextual cues, past experience, social, and motivational states) are taken into account. Here, we attempt to lay out current TMS studies assessing this issue and discuss the results in terms of their potential to favor the inner replica or the top-down modulation hypothesis. In doing so, we seek to shed light on this actual debate and suggest specific avenues for future research, highlighting the need for a more ecological approach when studying motor resonance phenomenon.

Sensorimotor cortex activation during anticipation of upcoming predictable but not unpredictable actions

The mirror neuron system (MNS) becomes active during action execution and action observation, which is presumably reflected by reductions in mu (8-13 Hz) activity in the electroencephalogram over the sensorimotor cortex. The function of the MNS is still fiercely debated. The current study aimed to investigate a role of the MNS in anticipating others' actions by examining whether the MNS was activated - indexed by mu power suppression - prior to the onset of observed actions when the onset and type of action could be predicted on the basis of environmental cues. Young adults performed and observed cued grasping and placing actions in a card game in a real-life setting, while the predictability of the observed actions was manipulated using rules. Significant mu suppression, relative to within-trial baseline activity, was found both prior to and during executed actions, but also during action observation, and, crucially, prior to observed actions provided they were predictable. No anticipatory mu reductions were found prior to unpredictable observed actions. These results suggest top-down modulation of MNS activity by conceptual knowledge. This is the first study to demonstrate mu suppression prior to action onset - possibly reflecting MNS anticipatory activity - by explicitly manipulating predictability.