Neural mirroring during the observation of live and video actions in infants

Uncomfortable staring? Gaze to other people in social situations is inhibited in both infants and adults

People attract infants' and adults' gaze when presented on a computer screen. However, in live social situations, adults inhibit their gaze at strangers to avoid sending inappropriate social signals. Such inhibition of gaze has never been directly investigated in infants. The current preregistered study measured gaze and neural responses (EEG alpha power) to a confederate in a live social situation compared to a video of this confederate. Adults looked less at the live confederate than at the video of the confederate, although their neural responses suggest that they were overall equally attentive in both situations. Infants also looked less at the live confederate than at the video of the confederate, with similar neural response patterns. The gaze difference between live social and video situations increased with age. The study shows that young infants are already sensitive to social context and show decreased gaze to strangers in social situations. RESEARCH HIGHLIGHTS: This study shows that infants and adults look more at a video of a stranger than at a stranger that is present live in a social situation. Neural responses suggest that adults are equally attentive in both live and video situations but inhibit their gaze at the stranger in live social situations. Infants show a similar pattern of shorter gaze at a stranger who is present in person than at a video of this stranger. The study shows that gaze in infants and adults may diverge from cognitive processes measured through EEG, highlighting the importance of combining behavioural and neural measures in natural interactions.

Live vs video interaction: sensorimotor and visual cortical oscillations during action observation

Increasingly, in the field of communication, education, and business, people are switching to video interaction, and interlocutors frequently complain that the perception of nonverbal information and concentration suffer. We investigated this issue by analyzing electroencephalogram (EEG) oscillations of the sensorimotor (mu rhythm) and visual (alpha rhythm) cortex of the brain in an experiment with action observation live and on video. The mu rhythm reflects the activity of the mirror neuron system, and the occipital alpha rhythm shows the level of visual attention. We used 32-channel EEG recorded during live and video action observation in 83 healthy volunteers. The ICA method was used for selecting the mu- and alpha-components; the Fourier Transform was used to calculate the suppression index relative to the baseline (stationary demonstrator) of the rhythms. The main range of the mu rhythm was indeed sensitive to social movement and was highly dependent on the conditions of interaction-live or video. The upper mu-range appeared to be less sensitive to the conditions, but more sensitive to different movements. The alpha rhythm did not depend on the type of movement; however, a live performance initially caused a stronger concentration of visual attention. Thus, subtle social and nonverbal perceptions may suffer in remote video interactions.

Down and up! Does the mu rhythm index a gating mechanism in the developing motor system?

Developmental research on action processing in the motor cortex relies on a key neural marker - a decrease in 6-12 Hz activity (coined mu suppression). However, recent evidence points towards an increase in mu power, specific for the observation of others' actions. Complementing the findings on mu suppression, this raises the critical question for the functional role of the mu rhythm in the developing motor system. We here discuss a potential solution to this seeming controversy by suggesting a gating function of the mu rhythm: A decrease in mu power may index the facilitation, while an increase may index the inhibition of motor processes, which are critical during action observation. This account may advance our conception of action understanding in early brain development and points towards critical directions for future research.

Sensorimotor anticipation of others' actions in real-world and video settings: modulation by level of engagement?

Electroencephalography (EEG) studies investigating social cognition have used both video and real-world stimuli, often without a strong reasoning why one or the other was chosen. Video stimuli can be selected for practical reasons, while naturalistic real-world stimuli are ecologically valid. The current study investigated modulatory effects on EEG mu (8 - 13 Hz) suppression, directly prior to the onset - and during the course - of observed actions, related to real-world and video settings. Recordings were made over sensorimotor cortex and stimuli in both settings consisted of identical (un)predictable object-related grasping and placing actions. In both settings a very similar mu suppression was found during unfolding of the action, irrespective of predictability. However, mu suppression related to the anticipation of upcoming predictable actions was found exclusively in the real-world setting. Thus, even though the presentation setting does not seem to modulate mu suppression during action observation, it does affect the anticipation-related mu suppression. We discuss the possibility that this may be due to increased social engagement in real-world settings, which in particular affects anticipation. The findings emphasise the importance of using real-world stimuli to bring out the subtle, anticipatory, aspects related to action observation.

Two-monkey fMRI setup for investigating multifaceted aspects of social cognition and behavior involving a real-live conspecific

While brain research over the past decades has shed light on the neural correlates of social cognition and behavior in human and non-human primates, most of this research has been performed in virtual settings requiring subjects to observe pictures or recorded videos instead of observing or interacting with another real-live individual. Here we present a two-monkey fMRI setup, allowing examining whole brain responses in macaque monkeys while they observe or interact face-to-face with another real-live conspecific. We tested this setup by comparing overall brain responses during observation of conspecific hand actions in a virtual (observation of recorded videos of actions) or live context (observation of a real-live conspecific performing actions). This dyadic monkey fMRI setup allows examining brain-wide responses in macaque monkeys during different aspects of social behavior, including observation of real-live actions and sensations, social facilitation, joint-attention and social interactions.

Mirroring Communicative Actions: Contextual Modulation of Mu Rhythm Desynchronization in Response to the 'Back-Of-Hand' Action in 9-Month-Old Infants

This study measured mu rhythm desynchronization (MRD), while nine-month-old infants observed an agent extend her arm and hand, palm up ('back-of-hand action') either in social (object and recipient present), individual (object present, recipient absent), or social object-absent (recipient present, object absent) situations across two experiments. In addition, infants' MRD was measured as they reached for objects. Results revealed significant mu desynchronization in the right centro-parietal region selectively for the social group, indicating that infants processed the back-of-hand action as an object-directed request. Findings suggest to extend the action reconstruction account to object-directed communicative actions as well.

Social EEG: A novel neurodevelopmental approach to studying brain-behavior links and brain-to-brain synchrony during naturalistic toddler-parent interactions

Despite increasing emphasis on emergent brain-behavior patterns supporting language, cognitive, and socioemotional development in toddlerhood, methodologic challenges impede their characterization. Toddlers are notoriously difficult to engage in brain research, leaving a developmental window in which neural processes are understudied. Further, electroencephalography (EEG) and event-related potential paradigms at this age typically employ structured, experimental tasks that rarely reflect formative naturalistic interactions with caregivers. Here, we introduce and provide proof of concept for a new "Social EEG" paradigm, in which parent-toddler dyads interact naturally during EEG recording. Parents and toddlers sit at a table together and engage in different activities, such as book sharing or watching a movie. EEG is time locked to the video recording of their interaction. Offline, behavioral data are microcoded with mutually exclusive engagement state codes. From 216 sessions to date with 2- and 3-year-old toddlers and their parents, 72% of dyads successfully completed the full Social EEG paradigm, suggesting that it is possible to collect dual EEG from parents and toddlers during naturalistic interactions. In addition to providing naturalistic information about child neural development within the caregiving context, this paradigm holds promise for examination of emerging constructs such as brain-to-brain synchrony in parents and children.

What modulates the Mirror Neuron System during action observation?: Multiple factors involving the action, the actor, the observer, the relationship between actor and observer, and the context

Seeing an agent perform an action typically triggers a motor simulation of that action in the observer's Mirror Neuron System (MNS). Over the past few years, it has become increasingly clear that during action observation the patterns and strengths of responses in the MNS are modulated by multiple factors. The first aim of this paper is therefore to provide the most comprehensive survey to date of these factors. To that end, 22 distinct factors are described, broken down into the following sets: six involving the action; two involving the actor; nine involving the observer; four involving the relationship between actor and observer; and one involving the context. The second aim is to consider the implications of these findings for four prominent theoretical models of the MNS: the Direct Matching Model; the Predictive Coding Model; the Value-Driven Model; and the Associative Model. These assessments suggest that although each model is supported by a wide range of findings, each one is also challenged by other findings and relatively unaffected by still others. Hence, there is now a pressing need for a richer, more inclusive model that is better able to account for all of the modulatory factors that have been identified so far.

Characterizing the Action-Observation Network Through Functional Near-Infrared Spectroscopy: A Review

Functional near-infrared spectroscopy (fNIRS) is a neuroimaging technique that has undergone tremendous growth over the last decade due to methodological advantages over other measures of brain activation. The action-observation network (AON), a system of brain structures proposed to have “mirroring” abilities (e.g., active when an individual completes an action or when they observe another complete that action), has been studied in humans through neural measures such as fMRI and electroencephalogram (EEG); however, limitations of these methods are problematic for AON paradigms. For this reason, fNIRS is proposed as a solution to investigating the AON in humans. The present review article briefly summarizes previous neural findings in the AON and examines the state of AON research using fNIRS in adults. A total of 14 fNIRS articles are discussed, paying particular attention to methodological choices and considerations while summarizing the general findings to aid in developing better protocols to study the AON through fNIRS. Additionally, future directions of this work are discussed, specifically in relation to researching AON development and potential multimodal imaging applications.

EEG measures of sensorimotor processing and their development are abnormal in children with isolated dystonia and dystonic cerebral palsy

Dystonia is a disorder of sensorimotor integration associated with abnormal oscillatory activity within the basal ganglia-thalamo-cortical networks. Event-related changes in spectral EEG activity reflect cortical processing but are sparsely investigated in relation to sensorimotor processing in dystonia. This study investigates modulation of sensorimotor cortex EEG activity in response to a proprioceptive stimulus in children with dystonia and dystonic cerebral palsy (CP). Proprioceptive stimuli, comprising brief stretches of the wrist flexors, were delivered via a robotic wrist interface to 30 young people with dystonia (20 isolated genetic/idiopathic and 10 dystonic CP) and 22 controls (mean age 12.7 years). Scalp EEG was recorded using the 10-20 international system and the relative change in post-stimulus power with respect to baseline was calculated for the alpha (8-12 Hz) and beta (14-30 Hz) frequency bands. A clear developmental profile in event-related spectral changes was seen in controls. Controls showed a prominent early alpha/mu band event-related desynchronisation (ERD) followed by an event-related synchronisation (ERS) over the contralateral sensorimotor cortex following movement of either hand. The alpha ERD was significantly smaller in the dystonia groups for both dominant and non-dominant hand movement (ANCOVA across the 3 groups with age as covariate: dominant hand F(2,47) = 4.45 p = 0.017; non-dominant hand F(2,42) = 9.397 p < 0.001. Alpha ERS was significantly smaller in dystonia for the dominant hand (ANCOVA F(2,47) = 7.786 p = 0.001). There was no significant difference in ERD or ERS between genetic/idiopathic dystonia and dystonic CP. CONCLUSION: Modulation of alpha/mu activity by a proprioceptive stimulus is reduced in dystonia, demonstrating a developmental abnormality of sensorimotor processing which is common to isolated genetic/idiopathic and acquired dystonia/dystonic CP.

Intention to imitate: Top-down effects on 4-year-olds' neural processing of others' actions

From early in life, we activate our neural motor system when observing others' actions. In adults, this so-called mirroring is modulated not only by the saliency of an action but also by top-down processes, like the intention to imitate it. Yet, it remains unknown whether neural processing of others' actions can be modulated by top-down processes in young children who heavily rely on learning from observing and imitating others but also still develop top-down control skills. Using EEG, we examined whether the intention to imitate increases 4-year-olds' motor activation while observing others' actions. In a within-subjects design, children observed identical actions preceded by distinct instructions, namely to either imitate the action or to name the toy's color. As motor activation index, children's alpha (7-12 Hz) and beta (16-20 Hz) power over motor cortices was analyzed. The results revealed more motor activity reflected by significantly lower beta power for the Imitation compared to the Color-naming Task. The same conditional difference, although differently located, was detected for alpha power. Together, our results show that children's neural processing of others' actions was amplified by their intention to imitate the action. Thus, already at age 4 top-down attention to others' actions can modulate neural action processing.

Developmental trajectory of interpersonal motor alignment: Positive social effects and link to social cognition

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Interpersonal motor alignment (IMA) has positive effects on healthy social life.

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IMA - mimicry, synchrony, automatic imitation - is studied throughout development.

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It relies on motor resonance brain mechanisms identified throughout development.

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It is modulated by contextual and personal factors.

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IMA is underinvestigated in adolescence, yet it may aid to enhance resilience.

Interpersonal motor alignment is a ubiquitous behavior in daily social life. It is a building block for higher social cognition, including empathy and mentalizing and promotes positive social effects. It can be observed as mimicry, synchrony and automatic imitation, to name a few. These phenomena rely on motor resonance processes, i.e., a direct link between the perception of an action and its execution. While a considerable literature debates its underlying mechanisms and measurement methods, the question of how motor alignment comes about and changes in ontogeny all the way until adulthood, is rarely discussed specifically. In this review we will focus on the link between interpersonal motor alignment, positive social effects and social cognition in infants, children, and adolescents, demonstrating that this link is present early on in development. Yet, in reviewing the existing literature pertaining to social psychology and developmental social cognitive neuroscience, we identify a knowledge gap regarding the healthy developmental changes in interpersonal motor alignment especially in adolescence.

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.

Exploring the EEG mu rhythm associated with observation and execution of a goal-directed action in 14-month-old preterm infants

Electroencephalographic mu rhythm desynchronization is thought to reflect Mirror Neuron System (MNS) activity and represents an important neural correlate of the coupling between action execution and perception. It is still unclear if the MNS in human ontogeny is already available at the beginning of postnatal life and how early experience impacts its development. Premature birth provides a "natural condition" for investigating the effects of early, atypical extra-uterine experience on MNS. The main aim of the present study was to investigate whether the MNS activity is associated with prematurity. We compared the mu rhythm activity in preterm (PT) and full-term (FT) 14-month old infants during an action observation/execution (AO/AE) task. Mu rhythm desynchronization was computed over frontal, central, parietal and occipital regions. Both groups showed mu rhythm suppression in all the scalp regions during action execution. Different desynchronization patterns emerged during action observation. Specifically, FT infants showed mu suppression in the right frontal, bilateral parietal and occipital regions; whereas PT infants exhibited mu suppression only in the right parietal region. Overall, these preliminary findings indicate that an atypical extra uterine experience might have an impact on the MNS activity.

Effects of live and video form action observation training on upper limb function in children with hemiparetic cerebral palsy

PURPOSE

The purpose of this study was to investigate the effects of live and video form action observation training (AOT) on upper limb (UL) movement acceleration and function in children with cerebral palsy (CP).

METHODS

In total, 12 children (7 boys, 5 girls) with CP participated in this study. The children were allocated randomly to live (experimental) and video (control) AOT groups. All children completed 20 treatment sessions, each 30 minutes in duration, 5 days per week for a month. Mediolateral (ML) and vertical (VT) acceleration data, Jebsen-Taylor Hand Function (JTHF) scores, and Box and Block Test (BBT) scores were obtained at baseline and at 4 weeks after the intervention.

RESULTS

ML and VT movement acceleration and JTHF scores were significantly lower in the live group (p< 0.05). The BBT score was significantly higher in the live than in the video group (p< 0.05).

CONCLUSIONS

Our findings suggest that live AOT is more effective than video AOT for improving UL movement acceleration and function. Clinically, our findings offer important insights for clinicians when planning AOT interventions to reduce UL movement acceleration and improve UL function.

A Social-Interactive Neuroscience Approach to Understanding the Developing Brain

From birth onward, social interaction is central to our everyday lives. Our ability to seek out social partners, flexibly navigate and learn from social interactions, and develop social relationships is critically important for our social and cognitive development and for our mental and physical health. Despite the importance of our social interactions, the neurodevelopmental bases of such interactions are underexplored, as most research examines social processing in noninteractive contexts. We begin this chapter with evidence from behavioral work and adult neuroimaging studies demonstrating how social-interactive context fundamentally alters cognitive and neural processing. We then highlight four brain networks that play key roles in social interaction and, drawing on existing developmental neuroscience literature, posit the functional roles these networks may play in social-interactive development. We conclude by discussing how a social-interactive neuroscience approach holds great promise for advancing our understanding of both typical and atypical social development.

Spatial and viewpoint selectivity for others' observed actions in monkey ventral premotor mirror neurons

The spatial location and viewpoint of observed actions are closely linked in natural social settings. For example, actions observed from a subjective viewpoint necessarily occur within the observer’s peripersonal space. Neurophysiological studies have shown that mirror neurons (MNs) of the monkey ventral premotor area F5 can code the spatial location of live observed actions. Furthermore, F5 MN discharge can also be modulated by the viewpoint from which filmed actions are seen. Nonetheless, whether and to what extent MNs can integrate viewpoint and spatial location of live observed actions remains unknown. We addressed this issue by comparing the activity of 148 F5 MNs while macaque monkeys observed an experimenter grasping in three different combinations of viewpoint and spatial location, namely, lateral view in the (1) extrapersonal and (2) peripersonal space and (3) subjective view in the peripersonal space. We found that the majority of MNs were space-selective (60.8%): those selective for the peripersonal space exhibited a preference for the subjective viewpoint both at the single-neuron and population level, whereas space-unselective neurons were view invariant. These findings reveal the existence of a previously neglected link between spatial and viewpoint selectivity in MN activity during live-action observation.

The Role of the Human Mirror Neuron System in Supporting Communication in a Digital World

Humans use both verbal and non-verbal communication to interact with others and their environment and increasingly these interactions are occurring in a digital medium. Whether live or digital, learning to communicate requires overcoming the correspondence problem: There is no direct mapping, or correspondence between perceived and self-produced signals. Reconciliation of the differences between perceived and produced actions, including linguistic actions, is difficult and requires integration across multiple modalities and neuro-cognitive networks. Recent work on the neural substrates of social learning suggests that there may be a common mechanism underlying the perception-production cycle for verbal and non-verbal communication. The purpose of this paper is to review evidence supporting the link between verbal and non-verbal communications, and to extend the hMNS literature by proposing that recent advances in communication technology, which at times have had deleterious effects on behavioral and perceptual performance, may disrupt the success of the hMNS in supporting social interactions because these technologies are virtual and spatiotemporal distributed nature.

Predictive action tracking without motor experience in 8-month-old infants

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Can infants predictively track the kinematics of actions outside their motor repertoire?

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Pre-walking infants predictively tracked upright, but not inverted stepping actions.

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Sensorimotor cortex was activated more when infants observed upright stepping actions.

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Motor experience is not necessary for predictive tracking of action kinematics.

A popular idea in cognitive neuroscience is that to predict others’ actions, observers need to map those actions onto their own motor repertoire. If this is true, infants with a relatively limited motor repertoire should be unable to predict actions with which they have no previous motor experience. We investigated this idea by presenting pre-walking infants with videos of upright and inverted stepping actions that were briefly occluded from view, followed by either a correct (time-coherent) or an incorrect (time-incoherent) continuation of the action (Experiment 1). Pre-walking infants looked significantly longer to the still frame after the incorrect compared to the correct continuations of the upright, but not the inverted stepping actions. This demonstrates that motor experience is not necessary for predictive tracking of action kinematics. In a follow-up study (Experiment 2), we investigated sensorimotor cortex activation as a neural indication of predictive action tracking in another group of pre-walking infants. Infants showed significantly more sensorimotor cortex activation during the occlusion of the upright stepping actions that the infants in Experiment 1 could predictively track, than during the occlusion of the inverted stepping actions that the infants in Experiment 1 could not predictively track. Taken together, these findings are inconsistent with the idea that motor experience is necessary for the predictive tracking of action kinematics, and suggest that infants may be able to use their extensive experience with observing others’ actions to generate real-time action predictions.

Examining ecological validity in social interaction: problems of visual fidelity, gaze, and social potential

Social interaction is an essential part of the human experience, and much work has been done to study it. However, several common approaches to examining social interactions in psychological research may inadvertently either unnaturally constrain the observed behaviour by causing it to deviate from naturalistic performance, or introduce unwanted sources of variance. In particular, these sources are the differences between naturalistic and experimental behaviour that occur from changes in visual fidelity (quality of the observed stimuli), gaze (whether it is controlled for in the stimuli), and social potential (potential for the stimuli to provide actual interaction). We expand on these possible sources of extraneous variance and why they may be important. We review the ways in which experimenters have developed novel designs to remove these sources of extraneous variance. New experimental designs using a 'two-person' approach are argued to be one of the most effective ways to develop more ecologically valid measures of social interaction, and we suggest that future work on social interaction should use these designs wherever possible.

Reduced engagement with social stimuli in 6-month-old infants with later autism spectrum disorder: a longitudinal prospective study of infants at high familial risk

Background

Autism spectrum disorder (ASD) is a neurodevelopmental disorder that affects more than 1 % of the population and close to 20 % of prospectively studied infants with an older sibling with ASD. Although significant progress has been made in characterizing the emergence of behavioral symptoms of ASD, far less is known about the underlying disruptions to early learning. Recent models suggest that core aspects of the causal path to ASD may only be apparent in early infancy. Here, we investigated social attention in 6- and 12-month-old infants who did and did not meet criteria for ASD at 24 months using both cognitive and electrophysiological methods. We hypothesized that a reduction in attention engagement to faces would be associated with later ASD.

Methods

In a prospective longitudinal design, we used measures of both visual attention (habituation) and brain function (event-related potentials to faces and objects) at 6 and 12 months and investigated the relationship to ASD outcome at 24 months.

Results

High-risk infants who met criteria for ASD at 24 months showed shorter epochs of visual attention, faster but less prolonged neural activation to faces, and delayed sensitization responses (increases in looking) to faces at 6 months; these differences were less apparent at 12 months. These findings are consistent with disrupted engagement of sustained attention to social stimuli.

Conclusions

These findings suggest that there may be fundamental early disruptions to attention engagement that may have cascading consequences for later social functioning.

Electronic supplementary material

The online version of this article (doi:10.1186/s11689-016-9139-8) contains supplementary material, which is available to authorized users.

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.

An EEG study on the somatotopic organisation of sensorimotor cortex activation during action execution and observation in infancy

Previous studies have shown that sensorimotor cortex activation is somatotopically-organised during action execution and observation in adulthood. Here we aimed to investigate the development of this phenomenon in infancy. We elicited arm and leg actions from 12-month-old infants and presented them, and a control group of adults, with videos of arm and leg actions while we measured their sensorimotor alpha suppression using EEG. Sensorimotor alpha suppression during action execution was somatotopically organised in 12-month-old infants: there was more suppression over the arm areas when infants performed reaching actions, and more suppression over the leg area when they performed kicking actions. Adults also showed somatotopically-organised activation during the observation of reaching and kicking actions. In contrast, infants did not show somatotopically-organised activation during action observation, but instead activated the arm areas when observing both reaching and kicking actions. We suggest that the somatotopic organisation of sensorimotor cortex activation during action observation may depend on infants' understanding of the action goal and their expectations about how this goal will be achieved.

Desynchronization in EEG during perception of means-end actions and relations with infants' grasping skill

The current study examined age-related differences in electroencephalogram (EEG) activity during perception of means-end actions and production of grasps, and how EEG activity may relate to infants' motor competence. We collected data from 9- and 12-month-old infants during perception of means-end actions made with a tool and during execution of their own grasps. We computed event-related desynchronization (ERD) during perception and production events and assessed infants' reach-grasp competence by looking at their latency to complete grasps. Although we found greater ERD during perception of means-end actions in 9-month-olds compared with 12-month-olds, we found the relation between ERD during perception and emerging reach-grasp competence to be specific for 12-month-olds and not for 9-month-olds. These results provide evidence for an emerging neural system that supports the coupling of action and perception with infants' emerging motor competence in the first year of life.

Developmental changes in infant brain activity during naturalistic social experiences

Between 6 and 12 months, typically developing infants undergo a socio-cognitive "revolution." The Interactive Specialization (IS) theory of brain development predicts that these behavioral changes will be underpinned by developmental increases in the power and topographic extent of socially selective cortical responses. To test this hypothesis, we used EEG to examine developmental changes in cortical selectivity for ecologically valid dynamic social versus non-social stimuli in a large cohort of 6- and 12-month-old infants. Consistent with the Interactive Specialization model, results showed that differences in EEG Θ activity between social and non-social stimuli became more pronounced and widespread with age. Differences in EEG activity were most clearly elicited by a live naturalistic interaction, suggesting that measuring brain activity in ecologically valid contexts is central to mapping social brain development in infancy.

Video stimuli reduce object-directed imitation accuracy: a novel two-person motion-tracking approach

Imitation is an important form of social behavior, and research has aimed to discover and explain the neural and kinematic aspects of imitation. However, much of this research has featured single participants imitating in response to pre-recorded video stimuli. This is in spite of findings that show reduced neural activation to video vs. real life movement stimuli, particularly in the motor cortex. We investigated the degree to which video stimuli may affect the imitation process using a novel motion tracking paradigm with high spatial and temporal resolution. We recorded 14 positions on the hands, arms, and heads of two individuals in an imitation experiment. One individual freely moved within given parameters (moving balls across a series of pegs) and a second participant imitated. This task was performed with either simple (one ball) or complex (three balls) movement difficulty, and either face-to-face or via a live video projection. After an exploratory analysis, three dependent variables were chosen for examination: 3D grip position, joint angles in the arm, and grip aperture. A cross-correlation and multivariate analysis revealed that object-directed imitation task accuracy (as represented by grip position) was reduced in video compared to face-to-face feedback, and in complex compared to simple difficulty. This was most prevalent in the left-right and forward-back motions, relevant to the imitator sitting face-to-face with the actor or with a live projected video of the same actor. The results suggest that for tasks which require object-directed imitation, video stimuli may not be an ecologically valid way to present task materials. However, no similar effects were found in the joint angle and grip aperture variables, suggesting that there are limits to the influence of video stimuli on imitation. The implications of these results are discussed with regards to previous findings, and with suggestions for future experimentation.

Brain representation of action observation in human infants

Imitative learning has long been established as extremely important for early development. However, neural mechanisms involved in early imitative behaviours are still areas of active research. Neurophysiological and brain-imaging studies have been recently performed that provide initial evidence of brain activation associated with action observation in the first months of life. In this review we examine all studies exploring the effects of action observation on brain function assessed by means of non-invasive brain-mapping techniques. Seventeen papers were selected as a result of our literature search. The strongest evidence for a neural signature of action observation comes from studies exploring the desynchronization of the μ-rhythm, which was reported for both occluded and visible goal-directed grasp, and was correlated with the totality of the infant's own action experience. The effects of action observation were reported on event-related potentials (ERPs) or near infrared spectroscopy. Taken together, these studies suggest that, in early infancy, a direct visual-motor matching process is already detectable as early as 6 months, suggesting a matching between action perception and execution already in infancy. If confirmed by future studies, these findings will shed light on the mechanisms of early motor development and imitation, and will be key to informing novel rehabilitation strategies in infants with congenital brain damage.

Neural mirroring mechanisms and imitation in human infants

Studying human infants will increase our understanding of the nature, origins and function of neural mirroring mechanisms. Human infants are prolific imitators. Infant imitation indicates observation-execution linkages in the brain prior to language and protracted learning. Investigations of neural aspects of these linkages in human infants have focused on the sensorimotor mu rhythm in the electroencephalogram, which occurs in the alpha frequency range over central electrode sites. Recent results show that the infant mu rhythm is desynchronized during action execution as well as action observation. Current work is elucidating properties of the infant mu rhythm and how it may relate to prelinguistic action processing and social understanding. Here, we consider this neuroscience research in relation to developmental psychological theory, particularly the 'Like-Me' framework, which holds that one of the chief cognitive tasks of the human infant is to map the similarity between self and other. We elucidate the value of integrating neuroscience findings with behavioural studies of infant imitation, and the reciprocal benefit of examining mirroring mechanisms from an ontogenetic perspective.

The Infant EEG Mu Rhythm: Methodological Considerations and Best Practices

The EEG mu rhythm, recorded from scalp regions overlying the sensorimotor cortex, appears to exhibit mirroring properties: It is reactive when performing an action and when observing another perform the same action. Recently, there has been an exponential increase in developmental mu rhythm research, partially due to the mu rhythm's potential role in our understanding of others' actions as well as a variety of other social and cognitive processes (e.g., imitation, theory of mind, language). Unfortunately, various methodological issues impede integrating these findings into a comprehensive theory of mu rhythm development. The present manuscript provides a review of the infant mu rhythm literature while focusing on current methodological problems that impede between study comparisons. By highlighting these issues and providing an in depth description and analysis we aim to heighten awareness and propose guidelines (when possible) that will promote rigorous infant mu rhythm research and facilitate between study comparisons. This paper is intended as a resource for developmental scientists, regardless of EEG expertise.