Perception of motion and qEEG activity in human adults

The capacity of action observation to drag the trainees' motor pattern toward the observed model

Action Observation Training (AOT) promotes the acquisition of motor abilities. However, while the cortical modulations associated with the AOT efficacy are well known, few studies investigated the AOT peripheral neural correlates and whether their dynamics move towards the observed model during the training. We administered seventy-two participants (randomized into AOT and Control groups) with training for learning to grasp marbles with chopsticks. Execution practice was preceded by an observation session, in which AOT participants observed an expert performing the task, whereas controls observed landscape videos. Behavioral indices were measured, and three hand muscles' electromyographic (EMG) activity was recorded and compared with the expert. Behaviorally, both groups improved during the training, with AOT outperforming controls. The EMG trainee-model similarity also increased during the training, but only for the AOT group. When combining behavioral and EMG similarity findings, no global relationship emerged; however, behavioral improvements were "locally" predicted by the similarity gain in muscles and action phases more related to the specific motor act. These findings reveal that AOT plays a magnetic role in motor learning, attracting the trainee's motor pattern toward the observed model and paving the way for developing online monitoring tools and neurofeedback protocols.

Activation of Cerebellum, Basal Ganglia and Thalamus During Observation and Execution of Mouth, hand, and foot Actions

Humans and monkey studies showed that specific sectors of cerebellum and basal ganglia activate not only during execution but also during observation of hand actions. However, it is unknown whether, and how, these structures are engaged during the observation of actions performed by effectors different from the hand. To address this issue, in the present fMRI study, healthy human participants were required to execute or to observe grasping acts performed with different effectors, namely mouth, hand, and foot. As control, participants executed and observed simple movements performed with the same effectors. The results show that: (1) execution of goal-directed actions elicited somatotopically organized activations not only in the cerebral cortex but also in the cerebellum, basal ganglia, and thalamus; (2) action observation evoked cortical, cerebellar and subcortical activations, lacking a clear somatotopic organization; (3) in the territories displaying shared activations between execution and observation, a rough somatotopy could be revealed in both cortical, cerebellar and subcortical structures. The present study confirms previous findings that action observation, beyond the cerebral cortex, also activates specific sectors of cerebellum and subcortical structures and it shows, for the first time, that these latter are engaged not only during hand actions observation but also during the observation of mouth and foot actions. We suggest that each of the activated structures processes specific aspects of the observed action, such as performing internal simulation (cerebellum) or recruiting/inhibiting the overt execution of the observed action (basal ganglia and sensory-motor thalamus).

Imitative and contagious behaviors in animals and their potential roles in the study of neurodevelopmental disorders

Social learning in the forms of imitative and contagious behaviors are essential for learning abilities and social interaction. However, children with neurodevelopmental disorders and intellectual disabilities show impairments in these behaviors, which profoundly affect their communication skills and cognitive functions. Although these deficits are well studied in humans, pre-clinical animal model assessments of imitative and contagious behavioral deficits are limited. Here, we first define various forms of social learning as well as their developmental and evolutionary significance in humans. We also explore the impact of imitative and contagious behavioral deficits in several neurodevelopmental disorders associated with autistic-like symptoms. Second, we highlight imitative and contagious behaviors observed in nonhuman primates and other social animals commonly used as models for neurodevelopmental disorders. Lastly, we conceptualize these behaviors in the contexts of mirror neuron activity, learning, and empathy, which are highly debated topics. Taken together, this review furthers the understanding of imitative and contagious behaviors. We hope to prompt and guide future behavioral studies in animal models of neurodevelopmental disorders.

Motor networks in children with autism spectrum disorder: a systematic review on EEG studies

Motor disturbance and altered motor networks are commonly reported in individuals with autism spectrum disorder (ASD). It has been suggested that electroencephalogram (EEG) can be used to provide exquisite temporal resolution for understanding motor control processes in ASD. However, the variability of study design and EEG approaches can impact our interpretation. Here, we conducted a systematic review on recent 11 EEG studies that involve motor observation and/or execution tasks and evaluated how these findings help us understand motor difficulties in ASD. Three behavior paradigms with different EEG analytic methods were demonstrated. The main findings were quite mixed: children with ASD did not always show disrupted neuronal activity during motor observation. Additionally, they might have intact ability for movement execution but have more difficulties in neuronal modulation during movement preparation. We would like to promote discussions on how methodological selections of behavioral tasks and data analytic approaches impact our interpretation of motor deficits in ASD. Future EEG research addressing the inconsistency across methodological approaches is necessary to help us understand neurophysiological mechanism of motor abnormalities in ASD.

The neural response is heightened when watching a person approaching compared to walking away: Evidence for dynamic social neuroscience

The action observation network has been proposed to play a key role in predicting the action intentions (or goals) of others, thereby facilitating social interaction. Key information when interacting with others is whether someone (an agent) is moving towards or away from us, indicating whether we are likely to interact with the person. In addition, to determine the nature of a social interaction, we also need to take into consideration the distance of the agent relative to us as the observer. How this kind of information is processed within the brain is unknown, at least in part because prior studies have not involved live whole-body motion. Consequently, here we recorded mobile EEG in 18 healthy participants, assessing the neural response to the modulation of direction (walking towards or away) and distance (near vs. far distance) during the observation of an agent walking. We evaluated whether cortical alpha and beta oscillations were modulated differently by direction and distance during action observation. We found that alpha was only modulated by distance, with a stronger decrease of power when the agent was further away from the observer, regardless of direction. Critically, by contrast, beta was found to be modulated by both distance and direction, with a stronger decrease of power when the agent was near and facing the participant (walking towards) compared to when they were near but viewed from the back (walking away). Analysis revealed differences in both the timing and distribution of alpha and beta oscillations. We argue that these data suggest a full understanding of action observation requires a new dynamic neuroscience, investigating actual interactions between real people, in real world environments.

Developmental Coordination Disorder: State of the Art and Future Directions from a Neurophysiological Perspective

Developmental coordination disorder (DCD) is a common neurodevelopmental condition characterized by disabling motor impairments being visible from the first years of life. Over recent decades, research in this field has gained important results, showing alterations in several processes involved in the regulation of motor behavior (e.g., planning and monitoring of actions, motor learning, action imitation). However, these studies mostly pursued a behavioral approach, leaving relevant questions open concerning the neural correlates of this condition. In this narrative review, we first survey the literature on motor control and sensorimotor impairments in DCD. Then, we illustrate the contributions to the field that may be achieved using transcranial magnetic stimulation (TMS) of the motor cortex. While still rarely employed in DCD research, this approach offers several opportunities, ranging from the clarification of low-level cortical electrophysiology to the assessment of the motor commands transmitted throughout the corticospinal system. We propose that TMS may help to investigate the neural correlates of motor impairments reported in behavioral studies, thus guiding DCD research toward a brain-oriented acknowledgment of this condition. This effort would help translational research to provide novel diagnostic and therapeutic tools.

Stepping in time: Alpha-mu and beta oscillations during a walking synchronization task

Interpersonal behavioral synchrony is referred to as temporal coordination of action between two or more individuals. Humans tend to synchronize their movements during repetitive movement tasks such as walking. Mobile EEG technology now allows us to examine how this happens during gait. 18 participants equipped with foot accelerometers and mobile EEG walked with an experimenter in three conditions: With their view of the experimenter blocked, walking naturally, and trying to synchronize their steps with the experimenter. The experimenter walked following a headphone metronome to keep their steps consistent for all conditions. Step behavior and synchronization between the experimenter and participant were compared between conditions. Additionally, event-related spectral perturbations (ERSPs) were time-warped to the gait cycle in order to analyze alpha-mu (7.5-12.5 Hz) and beta (16-32 Hz) rhythms over the whole gait cycle. Step synchronization was significantly higher in the synchrony condition than in the natural condition. Likewise regarding ERSPs, right parietal channel (C4, C6, CP4, CP6) alpha-mu and central channel (C1, Cz, C2) beta power were suppressed from baseline in the walking synchrony condition compared to the natural walking condition. The natural and blocked conditions were not found to be significantly different in behavioral or spectral comparisons. Our results are compatible with the view that intentional synchronization employs systems associated with social interaction as well as the central motor system.

Human mirror neuron system responsivity to unimodal and multimodal presentations of action

This study aims to clarify unresolved questions from two earlier studies by McGarry et al. Exp Brain Res 218(4): 527-538, 2012 and Kaplan and Iacoboni Cogn Process 8: 103-113, 2007 on human mirror neuron system (hMNS) responsivity to multimodal presentations of actions. These questions are: (1) whether the two frontal areas originally identified by Kaplan and Iacoboni (ventral premotor cortex [vPMC] and inferior frontal gyrus [IFG]) are both part of the hMNS (i.e., do they respond to execution as well as observation), (2) whether both areas yield effects of biologicalness (biological, control) and modality (audio, visual, audiovisual), and (3) whether the vPMC is preferentially responsive to multimodal input. To resolve these questions about the hMNS, we replicated and extended McGarry et al.'s electroencephalography (EEG) study, while incorporating advanced source localization methods. Participants were asked to execute movements (ripping paper) as well as observe those movements across the same three modalities (audio, visual, and audiovisual), all while 64-channel EEG data was recorded. Two frontal sources consistent with those identified in prior studies showed mu event-related desynchronization (mu-ERD) under execution and observation conditions. These sources also showed a greater response to biological movement than to control stimuli as well as a distinct visual advantage, with greater responsivity to visual and audiovisual compared to audio conditions. Exploratory analyses of mu-ERD in the vPMC under visual and audiovisual observation conditions suggests that the hMNS tracks the magnitude of visual movement over time.

Impact of Visual Design Elements and Principles in Human Electroencephalogram Brain Activity Assessed with Spectral Methods and Convolutional Neural Networks

The visual design elements and principles (VDEPs) can trigger behavioural changes and emotions in the viewer, but their effects on brain activity are not clearly understood. In this paper, we explore the relationships between brain activity and colour (cold/warm), light (dark/bright), movement (fast/slow), and balance (symmetrical/asymmetrical) VDEPs. We used the public DEAP dataset with the electroencephalogram signals of 32 participants recorded while watching music videos. The characteristic VDEPs for each second of the videos were manually tagged for by a team of two visual communication experts. Results show that variations in the light/value, rhythm/movement, and balance in the music video sequences produce a statistically significant effect over the mean absolute power of the Delta, Theta, Alpha, Beta, and Gamma EEG bands (p < 0.05). Furthermore, we trained a Convolutional Neural Network that successfully predicts the VDEP of a video fragment solely by the EEG signal of the viewer with an accuracy ranging from 0.7447 for Colour VDEP to 0.9685 for Movement VDEP. Our work shows evidence that VDEPs affect brain activity in a variety of distinguishable ways and that a deep learning classifier can infer visual VDEP properties of the videos from EEG activity.

Age-related Differences in Mu rhythm during Emotional Destination Memory

BACKGROUND

Destination memory, defined as the ability to remember to whom we addressed a piece of information, is found to be impaired in normal aging. Theories on development of affect and research findings have shown that emotional charge improves performance in memory tasks, and also that Mu rhythm is desynchronized as an index of mirror neuron activation during such tasks.

OBJECTIVE

In this paper, we sought to investigate the differences in Mu rhythm during an emotional destination memory task between younger and older adults.

METHODS

16 cognitively normal older adults, recruited from Alzheimer's disease day center and 16 young adults, recruited via advertisements, participated in this experimental study. We investigated the destination memory of emotionally charged faces (Emotional Destination Memory, EDM) while applying electroencephalograph (EEG) in real-time in young versus older adults. We measured Mu rhythm in frontal, fronto-temporal and central areas. EEG data has been pre-processed, segmented in non-overlapping epochs, and independent component analysis (ICA) has been conducted to reject artifacts.

RESULTS

Results showed that young adults performed better than older adults in remembering facts associated with angry faces. Also, a difference in neurophysiological activation was found, with older adults showing Mu suppression in frontal and fronto-temporal regions, specifically in F3, F7 and F8 electrodes, in contrast with young adults who showed Mu enhancement. With regard to the within-group differences, it was found that in the older adults group, electrodes F8 and central C3 were the most activated, while in the young adults group, C3 was the most activated electrode.

CONCLUSION

The findings suggest better behavioral performance of young adults as a result of a better cognitive state and adaptive bias. On a neurophysiological level, it is suggested that older adults employ Mu suppression, thus activation of mirror neurons is a possible compensatory mechanism while mirroring properties are not spontaneously activated in young adults.

Crossing hands behind your back reduces recall of manual action sentences and alters brain dynamics

The embodied meaning approach posits that understanding action-related language recruits motor processes in the brain. However, the functional impact of these motor processes on cognition has been questioned. The present study aims to provide new electrophysiological (EEG) evidence concerning the role of motor processes in the comprehension and memory of action language. Participants read lists of sentences including manual-action or attentional verbs, while keeping their hands either in front of them or crossing them behind their back. Results showed that posture impacted selectively the processing of manual action sentence, and not of attentional sentences, in three different ways: 1) EEG fronto-central beta rhythms, a signature of motor processes, were desynchronized while reading action sentences in the hands-in-front posture compared to the hands-behind posture. The estimated source was the posterior cingulate cortex, involved in proprioceptive regulation. 2) Recall of nouns associated with manual sentences decreased when learning occurred in the hands-behind posture. 3) ERPs analysis revealed that the initial posture at learning modulates neural processes during subsequent recall of manual sentences in the left superior frontal gyrus, which is related to motor processes. These results provide decisive evidence for the functional involvement of embodied simulations in the encoding and retrieval of action-related language.

Phase-coupling of neural oscillations contributes to individual differences in peripersonal space

The peripersonal space (PPS) is a multisensory and sensorimotor interface between our body and the environment. The location of PPS boundary is not fixed. Rather, it adapts to the environmental context and differs greatly across individuals. Recent studies have started to unveil the neural correlates of individual differences in PPS extension; however, this picture is not clear yet. Here, we used approaching auditory stimuli and magnetoencephalography to capture the individual boundary of PPS and examine its neural underpinnings. In particular, building upon previous studies from our own group, we investigated the possible contribution of an intrinsic feature of the brain, that is the "resting state" functional connectivity, to the individual differences in PPS extension and the frequency specificity of this contribution. Specifically, we focused on the activity synchronized to the premotor cortex, where multisensory neurons encoding PPS have been described. Results showed that the stronger the connectivity between left premotor cortex (lPM) and a set of fronto-parietal, sensorimotor regions in the right and left hemisphere, the wider the extension of the PPS. Strikingly, such a correlation was observed only in the beta-frequency band. Overall, our results suggest that the individual extension of the PPS is coded in spatially- and spectrally-specific resting state functional links.

Development of a flickering action video based steady state visual evoked potential triggered brain computer interface-functional electrical stimulation for a rehabilitative action observation game

BACKGROUND:

This study focused on developing an upper limb rehabilitation program. In this regard, a steady state visual evoked potential (SSVEP) triggered brain computer interface (BCI)-functional electrical stimulation (FES) based action observation game featuring a flickering action video was designed.

OBJECTIVE:

In particular, the synergetic effect of the game was investigated by combining the action observation paradigm with BCI based FES.

METHODS:

The BCI-FES system was contrasted under two conditions: with flickering action video and flickering noise video. In this regard, 11 right-handed subjects aged between 22–27 years were recruited. The differences in brain activation in response to the two conditions were examined.

RESULTS:

The results indicate that T3 and P3 channels exhibited greater Mu suppression in 8–13 Hz for the action video than the noise video. Furthermore, T4, C4, and P4 channels indicated augmented high beta (21–30 Hz) for the action in contrast to the noise video. Finally, T4 indicated suppressed low beta (14–20 Hz) for the action video in contrast to the noise video.

CONCLUSION:

The flickering action video based BCI-FES system induced a more synergetic effect on cortical activation than the flickering noise based system.

The impact of body posture on intrinsic brain activity: The role of beta power at rest

Tying the hands behind the back has detrimental effects on sensorimotor perceptual tasks. Here we provide evidence that beta band oscillatory activity in a resting state condition might play a crucial role in such detrimental effects. EEG activity at rest was measured from thirty young participants (mean age = 24.03) in two different body posture conditions. In one condition participants were required to keep their hands freely resting on the table. In the other condition, participants' hands were tied behind their back. Increased beta power was observed in the left inferior frontal gyrus during the tied hands condition compared to the free hands condition. A control experiment ruled out alternative explanations for observed change in beta power, including muscle tension. Our findings provide new insights on how body postural manipulations impact on perceptual tasks and brain activity.

Event-related desynchronization possibly discriminates the kinesthetic illusion induced by visual stimulation from movement observation

Visual stimulation of a repetitive self-movement image can evoke kinesthetic illusion when a virtual body part is set over the actual body part (kinesthetic illusion induced by visual stimulation, KINVIS). KINVIS induces activity in cerebral network, similar to that produced during motor execution, and triggers motor imagery passively. This study sought to identify a biomarker of KINVIS using event-related desynchronization (ERD) to improve the application of KINVIS to brain-machine interface (BMI) therapy of patients with stroke with hemiparesis. We included healthy adults in whom KINVIS could be induced. Scalp electroencephalograms were recorded during the KINVIS condition, where KINVIS was induced using a self-movement image. The findings were compared to signals recorded during an observation (OB) condition where only the self-movement image was viewed. For the signal intensity of the α- and low β-frequency bands, we calculated ERD during a movie period. The ERD of the α-frequency band in P3 and CP3 during KINVIS was significantly higher than that during OB. Furthermore, using the ERD of the α-frequency band recorded from FC3 and CP3, we could discriminate illusory perception with a 70% success rate. In this study, KINVIS could be detected using the ERD of the α-frequency band recorded from the posterior portion of the sensorimotor cortex. Furthermore, adding ERD recorded from FC3 to that recorded from CP3 may enable the objective discrimination of KINVIS from OB. When applying KINVIS in BMI therapy, the combination ERD of FC3 and CP3 will become a parameter for objectively judging the degree of kinesthetic perception achieved.

Musical Role Asymmetries in Piano Duet Performance Influence Alpha-Band Neural Oscillation and Behavioral Synchronization

Recent work in interpersonal coordination has revealed that neural oscillations, occurring spontaneously in the human brain, are modulated during the sensory, motor, and cognitive processes involved in interpersonal interactions. In particular, alpha-band (8-12 Hz) activity, linked to attention in general, is related to coordination dynamics and empathy traits. Researchers have also identified an association between each individual's attentiveness to their co-actor and the relative similarity in the co-actors' roles, influencing their behavioral synchronization patterns. We employed music ensemble performance to evaluate patterns of behavioral and neural activity when roles between co-performers are systematically varied with complete counterbalancing. Specifically, we designed a piano duet task, with three types of co-actor dissimilarity, or asymmetry: (1) musical role (starting vs. joining), (2) musical task similarity (similar vs. dissimilar melodic parts), and (3) performer animacy (human-to-human vs. human-to-non-adaptive computer). We examined how the experience of these asymmetries in four initial musical phrases, alternatingly played by the co-performers, influenced the pianists' performance of a subsequent unison phrase. Electroencephalography was recorded simultaneously from both performers while playing keyboards. We evaluated note-onset timing and alpha modulation around the unison phrase. We also investigated whether each individual's self-reported empathy was related to behavioral and neural activity. Our findings revealed closer behavioral synchronization when pianists played with a human vs. computer partner, likely because the computer was non-adaptive. When performers played with a human partner, or a joining performer played with a computer partner, having a similar vs. dissimilar musical part did not have a significant effect on their alpha modulation immediately prior to unison. However, when starting performers played with a computer partner with a dissimilar vs. similar part there was significantly greater alpha synchronization. In other words, starting players attended less to the computer partner playing a similar accompaniment, operating in a solo-like mode. Moreover, this alpha difference based on melodic similarity was related to a difference in note-onset adaptivity, which was in turn correlated with performer trait empathy. Collectively our results extend previous findings by showing that musical ensemble performance gives rise to a socialized context whose lasting effects encompass attentiveness, perceptual-motor coordination, and empathy.

The Post-Movement Beta Rebound and Motor-Related Mu Suppression in Children

Age-related EEG activity change is a prominent feature that reflects the functional development of the brain. The current study investigated the beta and mu rhythms of 16 children (7.7 ± 1.5 years, 5 to 9.6 years) and 13 adults when a self-determining arm motion was performed. The results indicated that mu power was decreased during movement and returned to baseline level after the movement for both children and adults. However, although a decrease in beta power was observed for both children and adults during movement, the post-movement beta power rebound (PMBR) was observed in adults but not in children. These results suggest that motor-related mu suppression develops early in children; PMBR develops later and may be associated with a more prolonged motor development process.

Observation of the point-light animation of a grasping hand activates sensorimotor cortex in nine-month-old infants

Measuring changes in sensorimotor alpha band activity in nine-month-old infants we sought to understand the involvement of the sensorimotor cortex during observation of the Point-Light (PL) animation of a grasping hand. Attenuation of alpha activity was found both when the PL display moved towards the to-be-grasped object and when the object was deleted from the video. Before the beginning of the movement of the PL stimuli, only in the presence of the object evoked attenuation of sensorimotor alpha activity was documented, possibly interpreted either as movement prediction or as graspable object perception. Our main findings demonstrate that, during observation of stimuli moving with biological kinematics, the infants' sensorimotor system is activated when the pictorial information is absent or highly reduced, and independently of the presence of the goal-directed object. The possible compensatory function of the sensorimotor system during observation of highly degraded moving stimuli is discussed.

Both the mirror and the affordance systems might be impaired in adults with high autistic traits. Evidence from EEG mu and beta rhythms

The association of autism spectrum disorder (ASD) with an altered mirror neuron system is still controversial. At the same time, the processing of object affordances by persons with ASD is a neglected issue. In this electroencephalographic study, adults differing in their autism quotient (AQ) scores were selected. We found anomalous modulation of mu and beta rhythms in high-AQ, compared to low-AQ persons, while they watched a set of goal-directed manual actions. This confirms that observing actions involving implicit intentions most clearly reveals the impairment of the mirror neurons system (MNS). The high-AQ group also showed anomalous mu and beta modulation when they looked at pictures of manipulable objects, indicating a deficit in processing motor affordances. We conclude that high-AQ adults have neural impairment of both the MNS and the affordance systems, which could underlie their relational problems with both people and objects. Autism Res 2019, 12: 1032-1042. © 2019 International Society for Autism Research, Wiley Periodicals, Inc. LAY SUMMARY: Adults with autistic traits (high-autism quotient [AQ] scores) and matched controls (low-AQ) observed intentional hand actions, and pictures of manipulable and non-manipulable objects. The high-AQ group compared to the control group, showed anomalous modulation of the electroencephalographic motoric rhythms (mu and beta) while observing familiar goal-directed actions, confirming an impairment of their mirror neuron system. Also, their brain rhythms were anomalous when they watched manipulable objects, which suggest a dysfunction in their relation with objects (affordance system).

Mental Simulation of Facial Expressions: Mu Suppression to the Viewing of Dynamic Neutral Face Videos

The mirror neuron network (MNN) has been proposed as a neural substrate of action understanding. Electroencephalography (EEG) mu suppression has commonly been studied as an index of MNN activity during execution and observation of hand and finger movements. However, in order to establish its role in higher order processes, such as recognizing and sharing emotions, more research using social emotional stimuli is needed. The current study aims to contribute to our understanding of the sensitivity of mu suppression to facial expressions. Modulation of the mu and occipital alpha (8-13 Hz) rhythms was calculated in 22 participants while they observed dynamic video stimuli, including emotional (happy and sad) and neutral (mouth opening) facial expressions, and non-biological stimulus (kaleidoscope pattern). Across the four types of stimuli, only the neutral face was associated with a significantly stronger mu suppression than the non-biological stimulus. Occipital alpha suppression was significantly greater in the non-biological stimulus than all the face conditions. Source estimation standardized low resolution electromagnetic tomography (sLORETA) analysis comparing the neural sources of mu/alpha modulation between neutral face and non-biological stimulus showed more suppression in the central regions, including the supplementary motor and somatosensory areas, than the more posterior regions. EEG and source estimation results may indicate that reduced availability of emotional information in the neutral face condition requires more sensorimotor engagement in deciphering emotion-related information than the full-blown happy or sad expressions that are more readily recognized.

Alpha band signatures of social synchrony

Previous research has reported changes in mu rhythm, the central rhythm of the alpha frequency band, in both intentional and spontaneous interpersonal coordination. The current study was designed to extend existing findings on social synchrony to the pendulum swinging task and simultaneously measured time unfolding behavioral synchrony and EEG estimation of mu activity during spontaneous, intentional in-phase and intentional anti-phase interpersonal coordination. As expected, the behavioral measures of synchrony demonstrated the expected pattern of weak synchronization for spontaneous coordination, moderate synchronization for intentional anti-phase coordination, and strong synchronization for in-phase coordination. With respect to the EEG measures, we found evidence for mu enhancement for spontaneous coordination in contrast to mu suppression for intentional coordination (both in phase and anti-phase), with higher levels of synchronization associated with higher levels of mu suppression in the right hemisphere. The implications of the research findings and methodology for understanding the underlying mechanisms contributing to social problems in psychological disorders, leader-follower relationships, and inter-brain dynamics are discussed.

Motor system recruitment during action observation: No correlation between mu-rhythm desynchronization and corticospinal excitability

Observing others’ actions desynchronizes electroencephalographic (EEG) rhythms and modulates corticospinal excitability as assessed by transcranial magnetic stimulation (TMS). However, it remains unclear if these measures reflect similar neurofunctional mechanisms at the individual level. In the present study, a within-subject experiment was designed to assess these two neurophysiological indexes and to quantify their mutual correlation. Participants observed reach-to-grasp actions directed towards a small (precision grip) or a large object (power grip). We focused on two specific time points for both EEG and TMS. The first time point (t1) coincided with the maximum hand aperture, i.e. the moment at which a significant modulation of corticospinal excitability is expected. The second (t2), coincided with the EEG resynchronization occurring at the end of the action, i.e. the moment at which a hypothetic minimum for action observation effect is expected. Results showed a Mu rhythm bilateral desynchronization at t1 with differential resynchronization at t2 in the two hemispheres. Beta rhythm was more desynchronized in the left hemisphere at both time points. These EEG differences, however, were not influenced by grip type. Conversely, motor potentials evoked by TMS in an intrinsic hand muscle revealed an interaction effect of grip and time. No significant correlations between Mu/Beta rhythms and motor evoked potentials were found. These findings are discussed considering the spatial and temporal resolution of the two investigated techniques and argue over two alternative explanations: i. each technique provides different measures of the same process or ii. they describe complementary features of the action observation network in humans.

When "Extraneous" Becomes "Mine". Neurophysiological Evidence of Sensorimotor Integration During Observation of Suboptimal Movement Patterns Performed by People with Multiple Sclerosis

Action observation is known to enhance sensorimotor system activation, and such effect has been linked to neural priming and response facilitation mechanisms. This facilitation effect, however, has been primarily studied by focusing on high-level motor proficiency, whereas evidence on the effect of observing poorly performed actions is still lacking. We then devised a study to investigate neural correlates of the observation of suboptimal motor acts as mirrored by corticospinal activation (via transcranial magnetic stimulation (TMS), Experiment 1) and by modulation of cortical oscillatory activity (via electroencephalography (EEG), Experiment 2). 40 participants were presented with four randomly reiterated videos. Videos depicted a healthy confederate, a minimally impaired multiple sclerosis (MS) patient, a mildly impaired MS patient, or a confederate trying to simulate mild motor difficulties performing a test concerning fine motor abilities. In Experiment 1 we analyzed TMS-induced motor-evoked potentials during the observation of videos. In Experiment 2 EEG data were analyzed in the frequency-domain. Analyses highlighted both increased corticospinal excitability and desynchronized alpha-beta oscillations during the observation of poorly performed motor acts performed by the mildly impaired MS patient. Further, we observed gradually increasing beta activity across videos reiterations, specifically for the minimally impaired patient's video. Reported findings corroborate the hypotheses that the action-observation network and the motor system might be involved in processes evoked in the attempt to understand and predict observed actions which do not belong to the onlookers' motor repertoire, reflecting in an increased sensorimotor activity.

Suppression of Sensorimotor Alpha Power Associated With Pain Expressed by an Avatar: A Preliminary EEG Study

Several studies using functional magnetic resonance imaging (fMRI) showed that empathic capabilities are associated with the activation (and deactivation) of relatively specific neural circuits. A growing number of electroencephalography studies also suggest that it might be useful to assess empathy. The main goal of this study was to use quantitative electroencephalography (qEEG) to test whether observation of pain expressed by an avatar (virtual reality) induces a suppression of alpha waves over sensorimotor cortical areas, as it is observed with human stimuli. Not only was it the case, but also the magnitude of alpha suppression was correlated with perspective-taking capacity of participants. Both empathy levels and magnitude of sensorimotor alpha suppression (SAS) were significantly higher in women than men. Interestingly, a significant interaction emerged between levels of individual empathy and specificity of experimental instructions, where SAS in participants with good perspective-taking was higher during passive observation of the distressed avatar, while the opposite was true during an active (trying to understand) condition. These results suggest that: (1) synthetic characters are able to elicit SAS; (2) SAS is indeed associated with perspective-taking capacities; (3) Persons with poorer perspective-taking capacities can show significant SAS when proper instructions are provided. Therefore, qEEG represents a low-cost objective approach to measure perspective-taking abilities.

Mu Suppression Is Sensitive to Observational Practice but Results in Different Patterns of Activation in Comparison with Physical Practice

Research has shown the effectiveness of observational practice for motor learning, but there continues to be debate about the mechanisms underlying effectiveness. Although cortical processes can be moderated during observation, after both physical and observational practice, how these processes change with respect to behavioural measures of learning has not been studied. Here we compared short-term physical and observational practice during the acquisition and retention of a novel motor task to evaluate how each type of practice modulates EEG mu rhythm (8-13 Hz). Thirty healthy individuals were randomly assigned to one of three groups: (1) physical practice (PP), (2) observational practice (OP), and (3) no practice (NP) control. There were four testing stages: baseline EEG, practice, postpractice observation, and delayed retention. There was significant bilateral suppression of mu rhythm during PP but only left lateralized mu suppression during OP. In the postpractice observation phase, mu suppression was bilateral and larger after PP compared to that after OP. NP control showed no evidence of suppression and was significantly different to both the OP and PP groups. When comparing the three groups in retention, the groups did not differ with respect to tracing times, but the PP group showed fewer errors, especially in comparison to the NP group. Therefore, although the neurophysiological measures index changes in the OP group, which are similar but moderated in comparison to PP, changes in these processes are not manifest in observational practice outcomes when assessed in a delayed retention test.

Simultaneous scalp recorded EEG and local field potentials from monkey ventral premotor cortex during action observation and execution reveals the contribution of mirror and motor neurons to the mu-rhythm

The desynchronization of alpha and beta oscillations (mu rhythm) in the central scalp EEG during action observation and action execution is thought to reflect neural mirroring processes. However, the extent to which mirror neurons (MNs) or other populations of neurons contribute to such EEG desynchronization is still unknown. Here, we provide the first evidence that, in the monkey, the neuronal activity recorded from the ventral premotor cortex (PMv) strongly contributes to the EEG changes occurring in the beta band over central scalp electrodes, during executed and observed actions. We simultaneously recorded scalp EEG and extracellular activity, Multi Unit Activity (MUA) and Local Field Potentials (LFP), from area F5 of two macaques executing and observing grasping actions. We found that MUA highly correlates with an increase in high gamma LFP power and, interestingly, such LFP power increase also correlates to EEG beta - and in part also to alpha - desynchronization. In terms of timing of signal changes, the increase in high gamma LFP power precedes the EEG desynchronization, during both action observation and execution, thus suggesting a causal role of PMv neuronal activity in the modulation of the alpha and beta mu-rhythm. Lastly, neuronal signals from deeper layers of PMv exert a greater contribution than superficial layers to the EEG beta rhythm modulation, especially during the motor task. Our findings have clear implications for EEG studies in that they demonstrate that the activity of different populations of neurons in PMv contribute to the generation of the mu-rhythm.

An Emotion-Enriched Context Influences the Effect of Action Observation on Cortical Excitability

Observing other people in action activates the “mirror neuron system” that serves for action comprehension and prediction. Recent evidence suggests that this function requires a high level codification triggered not only by components of motor behavior, but also by the environment where the action is embedded. An overlooked component of action perceiving is the one related to the emotional information provided by the context where the observed action takes place. Indeed, whether valence and arousal associated to an emotion might exert an influence on motor system activation during action observation has not been assessed so far. Here, cortico-spinal excitability of the left motor cortex was recorded in three groups of subjects. In the first condition, motor-evoked potential (MEPs) were recorded from a muscle involved in the grasping movement (i.e., abductor pollicis brevis, APB) while participants were watching the same reach-to-grasp movement embedded in contexts with negative emotional valence, but different levels of arousal: sadness (low arousal), and disgust (high arousal) (“Context plus Movement-APB” condition). In the second condition, MEPs were recorded from APB muscle while participants were observing static images representing the contexts in which the movement observed by participants in “Context plus Movement-APB” condition took place (“Context Only-APB” condition). Finally, in the third condition, MEPS were recorded from a muscle not involved in the grasping action, i.e., abductor digiti minimi, ADM, while participants were watching the same videos shown during the “Context plus Movement-APB” condition (“Context plus Movement-ADM” condition). Results showed a greater increase of cortical excitability only during the observation of the hand moving in the context eliciting disgust, and these changes were specific for the muscle involved in the observed action. Our findings show that the emotional context in which a movement occurs modulates motor resonance and that the combination of negative valence/high arousal drives the greater response in the observer’s mirror neuron system in a strictly muscle specific fashion.

When the Sound Becomes the Goal. 4E Cognition and Teleomusicality in Early Infancy

In this paper we explore early musical behaviors through the lenses of the recently emerged "4E" approach to mind, which sees cognitive processes as Embodied, Embedded, Enacted, and Extended. In doing so, we draw from a range of interdisciplinary research, engaging in critical and constructive discussions with both new findings and existing positions. In particular, we refer to observational research by French pedagogue and psychologist François Delalande, who examined infants' first "sound discoveries" and individuated three different musical "conducts" inspired by the "phases of the game" originally postulated by Piaget. Elaborating on such ideas we introduce the notion of "teleomusicality," which describes the goal-directed behaviors infants adopt to explore and play with sounds. This is distinguished from the developmentally earlier "protomusicality," which is based on music-like utterances, movements, and emotionally relevant interactions (e.g., with primary caregivers) that do not entail a primary focus on sound itself. The development from protomusicality to teleomusicality is discussed in terms of an "attentive shift" that occurs between 6 and 10 months of age. This forms the basis of a conceptual framework for early musical development that emphasizes the emergence of exploratory, goal-directed (i.e., sound-oriented), and self-organized musical actions in infancy. In line with this, we provide a preliminary taxonomy of teleomusical processes discussing "Original Teleomusical Acts" (OTAs) and "Constituted Teleomusical Acts" (CTAs). We argue that while OTAs can be easily witnessed in infants' exploratory behaviors, CTAs involve the mastery of more specific and complex goal-directed chains of actions central to musical activity.

Human Movement Responses to the Rorschach and Mirroring Activity: An fMRI Study

It has been suggested that the Rorschach human movement (M) response could be associated with an embodied simulation mechanism mediated by the mirror neuron system (MNS). To date, evidence for this hypothesis comes from two electroencephalogram studies and one repetitive transcranial magnetic stimulation study. To provide additional data on this topic, the Rorschach was administered during fMRI to a sample of 26 healthy adult volunteers. Activity in MNS-related brain areas temporally associated with M responses was compared with such activity for other, non-M Rorschach responses. Data analyses focused on MNS regions of interest identified by Neurosynth, a web-based platform for large scale, automated meta-analysis of fMRI data. Consistent with the hypothesis that M responses involve embodied simulation and MNS activity, univariate region of interest analyses showed that production of M responses associated with significantly greater activity in MNS-related brain areas when compared with non-M Rorschach responses. This finding is consistent with the traditional interpretation of the M code.

Flickering exercise video produces mirror neuron system (MNS) activation and steady state visually evoked potentials (SSVEPs)

The action of observing can be used as an effective rehabilitation paradigm, because it activates the mirror neuron system. However, it is difficult to fully use this paradigm because it is difficult to get patients to engage in watching video clips of exercise. In this study, we proposed a steady state visually evoked potential (SSVEP) based paradigm that could be used in a Brain Computer Interface, and examined its feasibility by investigating whether flickering video could activate the mirror neuron system and evoke SSVEPs at the same time. Twenty subjects were recruited and asked to watch the flickering videos at a rate of 20 Hz of upper limb motion and visual white noise, while an EEG signal was recorded. The mu rhythm (8-13 Hz) suppression and the SSVEP (19-21 Hz) evocation were analyzed from recorded EEG. The results showed that SSVEPs, evoked by the flickering stimulus, was observed in both conditions on O1 and O2, but the mu rhythm suppression on C3 and C4 was observed only in the exercise video condition. These results could signify that the flickering video is applicable for the BCI rehabilitation game, activating the mirror neuron system at the same time.

Perception of Peripersonal and Interpersonal Space in Patients with Restrictive-type Anorexia

This study examines whether the perception of peripersonal action-space and interpersonal social-space is modified in patients with restrictive-type anorexia in two experimental conditions using videos. First, participants stopped the video of an approaching stimulus when they felt the distance to be comfortable for interacting with it (first-person perspective). Second, participants stopped the video when an observed individual approaching a stimulus, or being approached by it, was at a comfortable distance (third-person perspective). In the first-person perspective, the results showed an estimation of peripersonal space that did not differ from controls when an object was approaching and an increase in interpersonal space compared with controls when a male or female individual was approaching. In the third-person perspective, both individual-object and individual-individual distances were larger in anorexic patients. These results indicate a specific deficit in adjusting interpersonal distances in both the first-person and third-person perspectives. Copyright © 2017 John Wiley & Sons, Ltd and Eating Disorders Association.

Frontal Functional Connectivity of Electrocorticographic Delta and Theta Rhythms during Action Execution Versus Action Observation in Humans

We have previously shown that in seven drug-resistant epilepsy patients, both reaching-grasping of objects and the mere observation of those actions did desynchronize subdural electrocorticographic (ECoG) alpha (8-13 Hz) and beta (14-30) rhythms as a sign of cortical activation in primary somatosensory-motor, lateral premotor and ventral prefrontal areas (Babiloni et al., 2016a). Furthermore, that desynchronization was greater during action execution than during its observation. In the present exploratory study, we reanalyzed those ECoG data to evaluate the proof-of-concept that lagged linear connectivity (LLC) between primary somatosensory-motor, lateral premotor and ventral prefrontal areas would be enhanced during the action execution compared to the mere observation due to a greater flow of visual and somatomotor information. Results showed that the delta-theta (<8 Hz) LLC between lateral premotor and ventral prefrontal areas was higher during action execution than during action observation. Furthermore, the phase of these delta-theta rhythms entrained the local event-related connectivity of alpha and beta rhythms. It was speculated the existence of a multi-oscillatory functional network between high-order frontal motor areas which should be more involved during the actual reaching-grasping of objects compared to its mere observation. Future studies in a larger population should cross-validate these preliminary results.

Quantitative electroencephalograms and neuro-optometry: a case study that explores changes in electrophysiology while wearing therapeutic eyeglasses

The brain is equipped with a complex system for processing sensory information, including retinal circuitry comprising part of the central nervous system. Retinal stimulation can influence brain function via customized eyeglasses at both subcortical and cortical levels. We investigated cortical effects from wearing therapeutic eyeglasses, hypothesizing that they can create measureable changes in electroencephalogram (EEG) tracings. A Z-Bell^SM test was performed on a participant to select optimal lenses. An EEG measurement was recorded before and after the participant wore the eyeglasses. Equivalent quantitative electroencephalography (QEEG) analyses (statistical analysis on raw EEG recordings) were performed and compared with baseline findings. With glasses on, the participant's readings were found to be closer to the normed database. The original objective of our investigation was met, and additional findings were revealed. The Z-bell^SM test identified lenses to influence neurotypical brain activity, supporting the paradigm that eyeglasses can be utilized as a therapeutic intervention. Also, EEG analysis demonstrated that encephalographic techniques can be used to identify channels through which neuro-optomertric treatments work. This case study's preliminary exploration illustrates the potential role of QEEG analysis and EEG-derived brain imaging in neuro-optometric research endeavors to affect brain function.

From movement kinematics to social cognition: the case of autism

The way in which we move influences our ability to perceive, interpret and predict the actions of others. Thus movements play an important role in social cognition. This review article will appraise the literature concerning movement kinematics and motor control in individuals with autism, and will argue that movement differences between typical and autistic individuals may contribute to bilateral difficulties in reciprocal social cognition.

A Comparison of Independent Event-Related Desynchronization Responses in Motor-Related Brain Areas to Movement Execution, Movement Imagery, and Movement Observation

Electroencephalographic (EEG) event-related desynchronization (ERD) induced by movement imagery or by observing biological movements performed by someone else has recently been used extensively for brain-computer interface-based applications, such as applications used in stroke rehabilitation training and motor skill learning. However, the ERD responses induced by the movement imagery and observation might not be as reliable as the ERD responses induced by movement execution. Given that studies on the reliability of the EEG ERD responses induced by these activities are still lacking, here we conducted an EEG experiment with movement imagery, movement observation, and movement execution, performed multiple times each in a pseudorandomized order in the same experimental runs. Then, independent component analysis (ICA) was applied to the EEG data to find the common motor-related EEG source activity shared by the three motor tasks. Finally, conditional EEG ERD responses associated with the three movement conditions were computed and compared. Among the three motor conditions, the EEG ERD responses induced by motor execution revealed the alpha power suppression with highest strengths and longest durations. The ERD responses of the movement imagery and movement observation only partially resembled the ERD pattern of the movement execution condition, with slightly better detectability for the ERD responses associated with the movement imagery and faster ERD responses for movement observation. This may indicate different levels of involvement in the same motor-related brain circuits during different movement conditions. In addition, because the resulting conditional EEG ERD responses from the ICA preprocessing came with minimal contamination from the non-related and/or artifactual noisy components, this result can play a role of the reference for devising a brain-computer interface using the EEG ERD features of movement imagery or observation.

Reputation in an economic game modulates premotor cortex activity during action observation

Our interactions with other people - and our processing of their actions - are shaped by their reputation. Research has identified an Action Observation Network (AON) which is engaged when observing other people's actions. Yet, little is known about how the processing of others' actions is influenced by another's reputation. Is the response of the AON modulated by the reputation of the actor? We developed a variant of the ultimatum game in which participants watched either the visible or occluded actions of two 'proposers'. These actions were tied to decisions of how to split a pot of money although the proposers' decisions on each trial were not known to participants when observing the actions. One proposer made fair offers on the majority of trials, establishing a positive reputation, whereas the other made predominantly, unfair offers resulting in a negative reputation. We found significant activations in two regions of the left dorsal premotor cortex (dPMC). The first of these showed a main effect of reputation with greater activation for the negative reputation proposer than the positive reputation proposer. Furthermore individual differences in trust ratings of the two proposers covaried with activation in the right primary motor cortex (M1). The second showed an interaction between visibility and reputation driven by a greater effect of reputation when participants were observing an occluded action. Our findings show that the processing of others' actions in the AON is modulated by an actor's reputation, and suggest a predictive role for the PMC during action observation.

Power modulation of electroencephalogram mu and beta frequency depends on perceived level of observed actions

INTRODUCTION

The ability to understand actions and intentions of others is of great importance to social relationships and is associated with the mirror neuron system of the human brain. Whether conscious perception of specific actions is necessary to trigger activity in this system, or alternatively whether this response is independent of conscious perception is not known.

METHODS

We addressed this issue by rendering videos of right hand movements invisible to conscious perception, and measuring electroencephalogram (EEG) power suppression in the mu (8-13 Hz) and beta (15-25 Hz) range as index corresponding to the magnitude of mirror neuron activity.

RESULTS

In the beta range over bilateral sensorimotor sites, we find that suppression indices follow the reported perceptual level of subjects with stronger suppression for consciously perceived trials. Furthermore, in the nonperceived trials, oscillation power is significantly suppressed relative to baseline. In the low mu range (8-10 Hz), oscillation power over the left sensorimotor site is significantly more suppressed in the consciously perceived versus nonperceived trials.

CONCLUSIONS

Our data suggest that the intensity of mirror system responses during action observation decreases with the observers' perception level yet remains significant during observation of invisible actions. Such subliminal activity could help explain phenomena such as covert imitation.

Exercise Performance and Corticospinal Excitability during Action Observation

Purpose: Observation of a model performing fast exercise improves simultaneous exercise performance; however, the precise mechanism underpinning this effect is unknown. The aim of the present study was to investigate whether the speed of the observed exercise influenced both upper body exercise performance and the activation of a cortical action observation network (AON).

Method: In Experiment 1, 10 participants completed a 5 km time trial on an arm-crank ergometer whilst observing a blank screen (no-video) and a model performing exercise at both a typical (i.e., individual mean cadence during baseline time trial) and 15% faster than typical speed. In Experiment 2, 11 participants performed arm crank exercise whilst observing exercise at typical speed, 15% slower and 15% faster than typical speed. In Experiment 3, 11 participants observed the typical, slow and fast exercise, and a no-video, whilst corticospinal excitability was assessed using transcranial magnetic stimulation.

Results: In Experiment 1, performance time decreased and mean power increased, during observation of the fast exercise compared to the no-video condition. In Experiment 2, cadence and power increased during observation of the fast exercise compared to the typical speed exercise but there was no effect of observation of slow exercise on exercise behavior. In Experiment 3, observation of exercise increased corticospinal excitability; however, there was no difference between the exercise speeds.

Conclusion: Observation of fast exercise improves simultaneous upper-body exercise performance. However, because there was no effect of exercise speed on corticospinal excitability, these results suggest that these improvements are not solely due to changes in the activity of the AON.

Cortical Spectral Activity and Connectivity during Active and Viewed Arm and Leg Movement

Active and viewed limb movement activate many similar neural pathways, however, to date most comparison studies have focused on subjects making small, discrete movements of the hands and feet. The purpose of this study was to determine if high-density electroencephalography (EEG) could detect differences in cortical activity and connectivity during active and viewed rhythmic arm and leg movements in humans. Our primary hypothesis was that we would detect similar but weaker electrocortical spectral fluctuations and effective connectivity fluctuations during viewed limb exercise compared to active limb exercise due to the similarities in neural recruitment. A secondary hypothesis was that we would record stronger cortical spectral fluctuations for arm exercise compared to leg exercise, because rhythmic arm exercise would be more dependent on supraspinal control than rhythmic leg exercise. We recorded EEG data while ten young healthy subjects exercised on a recumbent stepper with: (1) both arms and legs, (2) just legs, and (3) just arms. Subjects also viewed video playback of themselves or another individual performing the same exercises. We performed independent component analysis, dipole fitting, spectral analysis, and effective connectivity analysis on the data. Cortical areas comprising the premotor and supplementary motor cortex, the anterior cingulate, the posterior cingulate, and the parietal cortex exhibited significant spectral fluctuations during rhythmic limb exercise. These fluctuations tended to be greater for the arms exercise conditions than for the legs only exercise condition, which suggests that human rhythmic arm movements are under stronger cortical control than rhythmic leg movements. We did not find consistent spectral fluctuations in these areas during the viewed conditions, but effective connectivity fluctuated at harmonics of the exercise frequency during both active and viewed rhythmic limb exercise. The right premotor and supplementary motor cortex drove the network. These results suggest that a similarly interconnected neural network is in operation during active and viewed human rhythmic limb movement.

Infants' Understanding of Object-Directed Action: An Interdisciplinary Synthesis

Recognizing that the object-directed actions of others are governed by goals and intentions is a crucial component of human interaction. These actions often occur rapidly and without explanation, yet we learn from and predict the actions of others with remarkable speed and accuracy, even during the first year of life. This review paper will serve as a bridge between several disparate literatures that, we suggest, can each contribute to our understanding of how infants interpret action. Specifically, we provide a review not just of research on infant goal attribution per se, but also incorporate findings from studies on the mirror neuron system and infant object cognition. The integration of these various research approaches allows for a novel construal of the extents and limits of early goal attribution – one in which the importance of the entire action context is considered – and points to specific future research directions.

Relations between infants' emerging reach-grasp competence and event-related desynchronization in EEG

Recent reports of similar patterns of brain electrical activity (electroencephalogram: EEG) during action execution and observation, recorded from scalp locations over motor-related regions in infants and adults, have raised the possibility that two foundational abilities--controlling one's own intentional actions and perceiving others' actions--may be integrally related during ontogeny. However, to our knowledge, there are no published reports of the relations between developments in motor skill (i.e. recording actual motor skill performance) and EEG during both action execution and action observation. In the present study we collected EEG from 21 9-month-olds who were given opportunities to reach for toys and who also observed an experimenter reach for toys. Event-related desynchronization (ERD) was computed from the EEG during the reaching events. We assessed infants' reaching-grasping competence, including reach latency, errors, preshaping of the hand, and bimanual reaches, and found that desynchronization recorded in scalp electrodes over motor-related regions during action observation was associated with action competence during execution. Infants who were more competent reachers, compared to less competent reachers, exhibited greater ERD while observing reaching-grasping. These results provide initial evidence for an early emerging neural system integrating one's own actions with the perception of others' actions.

Assessing human mirror activity with EEG mu rhythm: A meta-analysis

A fundamental issue in cognitive neuroscience is how the brain encodes others' actions and intentions. In recent years, a potential advance in our knowledge on this issue is the discovery of mirror neurons in the motor cortex of the nonhuman primate. These neurons fire to both execution and observation of specific types of actions. Researchers use this evidence to fuel investigations of a human mirror system, suggesting a common neural code for perceptual and motor processes. Among the methods used for inferring mirror system activity in humans are changes in a particular frequency band in the electroencephalogram (EEG) called the mu rhythm. Mu frequency appears to decrease in amplitude (reflecting cortical activity) during both action execution and action observation. The current meta-analysis reviewed 85 studies (1,707 participants) of mu that infer human mirror system activity. Results demonstrated significant effect sizes for mu during execution (Cohen's d = 0.46, N = 701) as well as observation of action (Cohen's d = 0.31, N = 1,508), confirming a mirroring property in the EEG. A number of moderators were examined to determine the specificity of these effects. We frame these meta-analytic findings within the current discussion about the development and functions of a human mirror system, and conclude that changes in EEG mu activity provide a valid means for the study of human neural mirroring. Suggestions for improving the experimental and methodological approaches in using mu to study the human mirror system are offered.

Embodied simulation and ambiguous stimuli: The role of the mirror neuron system

According to the "embodied simulation theory," exposure to certain visual stimuli would automatically trigger action simulation in the mind of the observer, thereby originating a "feeling of movement" modulated by the mirror neuron system (MNS). Grounded on this conceptualization, some of us recently suggested that when exposed to the Rorschach inkblots, in order to see a human movement (e.g., "a person running") in those ambiguous stimuli, the observer would need to experience a "feeling of movement" via embodied simulation. The current study used repetitive transcranial magnetic stimulation (rTMS) to further test this hypothesis. Specifically, we investigated whether temporarily interfering with the activity of the left inferior frontal gyrus (LIFG; a putative MNS area) using rTMS would decrease the propensity to see human movement (M) in the Rorschach inkblots. Thirty-six participants were exposed to the Rorschach stimuli twice, i.e., during a baseline (without rTMS) and soon after inhibitory rTMS. As for the rTMS condition, half of the sample was stimulated over the LIFG (experimental group) and the other half over the Vertex (control group). In line with our hypothesis, the application of rTMS over LIFG, but not over Vertex, yielded a statistically significant reduction in the attribution of M to the ambiguous stimuli, with large effect size. These findings may be interpreted as being consistent with the hypothesis that there is a link between the MNS and the "feeling of movement" people may experience, when observing ambiguous stimuli such as the Rorschach cards.