The mirror neuron system as revealed through neonatal imitation: presence from birth, predictive power and evidence of plasticity

A proposal for new neurorehabilitative intervention on Moebius Syndrome patients after 'smile surgery'. Proof of concept based on mirror neuron system properties and hand-mouth synergistic activity

Studies of the last twenty years on the motor and premotor cortices of primates demonstrated that the motor system is involved in the control and initiation of movements, and in higher cognitive processes, such as action understanding, imitation, and empathy. Mirror neurons are only one example of such theoretical shift. Their properties demonstrate that motor and sensory processing are coupled in the brain. Such knowledge has been also central for designing new neurorehabilitative therapies for patients suffering from brain injuries and consequent motor deficits. Moebius Syndrome patients, for example, are incapable of moving their facial muscles, which are fundamental for affective communication. These patients face an important challenge after having undergone a corrective surgery: reanimating the transplanted muscles to achieve a voluntarily control of smiling. We propose two new complementary rehabilitative approaches on MBS patients based on observation/imitation therapy (Facial Imitation Therapy, FIT) and on hand-mouth motor synergies (Synergistic Activity Therapy, SAT). Preliminary results show that our intervention protocol is a promising approach for neurorehabilitation of patients with facial palsy.

Re-examination of Oostenbroek et al. (2016): evidence for neonatal imitation of tongue protrusion

The meaning, mechanism, and function of imitation in early infancy have been actively discussed since Meltzoff and Moore's (1977) report of facial and manual imitation by human neonates. Oostenbroek et al. (2016) claim to challenge the existence of early imitation and to counter all interpretations so far offered. Such claims, if true, would have implications for theories of social-cognitive development. Here we identify 11 flaws in Oostenbroek et al.'s experimental design that biased the results toward null effects. We requested and obtained the authors' raw data. Contrary to the authors' conclusions, new analyses reveal significant tongue-protrusion imitation at all four ages tested (1, 3, 6, and 9 weeks old). We explain how the authors missed this pattern and offer five recommendations for designing future experiments. Infant imitation raises fundamental issues about action representation, social learning, and brain-behavior relations. The debate about the origins and development of imitation reflects its importance to theories of developmental science.

Handling newborn monkeys alters later exploratory, cognitive, and social behaviors

Touch is one of the first senses to develop and one of the earliest modalities for infant-caregiver communication. While studies have explored the benefits of infant touch in terms of physical health and growth, the effects of social touch on infant behavior are relatively unexplored. Here, we investigated the influence of neonatal handling on a variety of domains, including memory, novelty seeking, and social interest, in infant monkeys (Macaca mulatta; n=48) from 2 to 12 weeks of age. Neonates were randomly assigned to receive extra holding, with or without accompanying face-to-face interactions. Extra-handled infants, compared to standard-reared infants, exhibited less stress-related behavior and more locomotion around a novel environment, faster approach of novel objects, better working memory, and less fear towards a novel social partner. In sum, infants who received more tactile stimulation in the neonatal period subsequently demonstrated more advanced motor, social, and cognitive skills-particularly in contexts involving exploration of novelty-in the first three months of life. These data suggest that social touch may support behavioral development, offering promising possibilities for designing future early interventions, particularly for infants who are at heightened risk for social disorders.

Neonatal Imitation: Theory, Experimental Design, and Significance for the Field of Social Cognition

Neonatal imitation has rich implications for neuroscience, developmental psychology, and social cognition, but there is little consensus about this phenomenon. The primary empirical question, whether or not neonatal imitation exists, is not settled. Is it possible to give a balanced evaluation of the theories and methodologies at stake so as to facilitate real progress with respect to the primary empirical question? In this paper, we address this question. We present the operational definition of differential imitation and discuss why it is important to keep it in mind. The operational definition indicates that neonatal imitation may not look like prototypical imitation and sets non-obvious requirements on what can count as evidence for imitation. We also examine the principal explanations for the extant findings and argue that two theories, the arousal hypothesis and the Association by Similarity Theory, which interprets neonatal imitation as differential induction of spontaneous behavior through similarity, offer better explanations than the others. With respect to methodology, we investigate what experimental design can best provide evidence for imitation, focusing on how differential induction may be maximized and detected. Finally, we discuss the significance of neonatal imitation for the field of social cognition. Specifically, we propose links with theories of social interaction and direct social perception. Overall, our goals are to help clarify the complex theoretical issues at stake and suggest fruitful guidelines for empirical research.

Testing the arousal hypothesis of neonatal imitation in infant rhesus macaques

Neonatal imitation is the matching of (often facial) gestures by newborn infants. Some studies suggest that performance of facial gestures is due to general arousal, which may produce false positives on neonatal imitation assessments. Here we examine whether arousal is linked to facial gesturing in newborn infant rhesus macaques (Macaca mulatta). We tested 163 infants in a neonatal imitation paradigm in their first postnatal week and analyzed their lipsmacking gestures (a rapid opening and closing of the mouth), tongue protrusion gestures, and yawn responses (a measure of arousal). Arousal increased during dynamic stimulus presentation compared to the static baseline across all conditions, and arousal was higher in the facial gestures conditions than the nonsocial control condition. However, even after controlling for arousal, we found a condition-specific increase in facial gestures in infants who matched lipsmacking and tongue protrusion gestures. Thus, we found no support for the arousal hypothesis. Consistent with reports in human newborns, imitators’ propensity to match facial gestures is based on abilities that go beyond mere arousal. We discuss optimal testing conditions to minimize potentially confounding effects of arousal on measurements of neonatal imitation.

Neonatal Hypoxia Ischaemia: Mechanisms, Models, and Therapeutic Challenges

Neonatal hypoxia-ischaemia (HI) is the most common cause of death and disability in human neonates, and is often associated with persistent motor, sensory, and cognitive impairment. Improved intensive care technology has increased survival without preventing neurological disorder, increasing morbidity throughout the adult population. Early preventative or neuroprotective interventions have the potential to rescue brain development in neonates, yet only one therapeutic intervention is currently licensed for use in developed countries. Recent investigations of the transient cortical layer known as subplate, especially regarding subplate's secretory role, opens up a novel set of potential molecular modulators of neonatal HI injury. This review examines the biological mechanisms of human neonatal HI, discusses evidence for the relevance of subplate-secreted molecules to this condition, and evaluates available animal models. Neuroserpin, a neuronally released neuroprotective factor, is discussed as a case study for developing new potential pharmacological interventions for use post-ischaemic injury.

Face proprioception does not modulate access to visual awareness of emotional faces in a continuous flash suppression paradigm

An important question in neuroscience is which multisensory information, presented outside of awareness, can influence the nature and speed of conscious access to our percepts. Recently, proprioceptive feedback of the hand was reported to lead to faster awareness of congruent hand images in a breaking continuous flash suppression (b-CFS) paradigm. Moreover, a vast literature suggests that spontaneous facial mimicry can improve emotion recognition, even without awareness of the stimulus face. However, integration of visual and proprioceptive information about the face to date has not been tested with CFS. The modulation of visual awareness of emotional faces by facial proprioception was investigated across three separate experiments. Face proprioception was induced with voluntary facial expressions or with spontaneous facial mimicry. Frequentist statistical analyses were complemented with Bayesian statistics. No evidence of multisensory integration was found, suggesting that proprioception does not modulate access to visual awareness of emotional faces in a CFS paradigm.

Neural mechanisms of vocal imitation: The role of sleep replay in shaping mirror neurons

Learning by imitation involves not only perceiving another individual's action to copy it, but also the formation of a memory trace in order to gradually establish a correspondence between the sensory and motor codes, which represent this action through sensorimotor experience. Memory and sensorimotor processes are closely intertwined. Mirror neurons, which fire both when the same action is performed or perceived, have received considerable attention in the context of imitation. An influential view of memory processes considers that the consolidation of newly acquired information or skills involves an active offline reprocessing of memories during sleep within the neuronal networks that were initially used for encoding. Here, we review the recent advances in the field of mirror neurons and offline processes in the songbird. We further propose a theoretical framework that could establish the neurobiological foundations of sensorimotor learning by imitation. We propose that the reactivation of neuronal assemblies during offline periods contributes to the integration of sensory feedback information and the establishment of sensorimotor mirroring activity at the neuronal level.

Development of rostral inferior parietal lobule area functional connectivity from late childhood to early adulthood

Although the mirror neuron system (MNS) has been extensively studied in monkeys and adult humans, very little is known about its development. Previous studies suggest that the MNS is present by infancy and that the brain and MNS-related cognitive abilities (such as language, empathy, and imitation learning) continue to develop after childhood. In humans, the PFt area of the inferior parietal lobule (IPL) seems to particularly correlate with the functional properties of the PF area in primates, which contains mirror neurons. However, little is known about the functional connectivity (FC) of the PFt area with other brain areas and whether these networks change over time. Here, we investigated the FC development of the PFt area-based network in 59 healthy subjects aged 7-26 years at resting-state to study brain development from late childhood through adolescence to early adulthood. The bilateral PFt showed similar core FC networks, which included the frontal lobe, the cingulate gyri, the insula, the somatosensory cortex, the precuneus, the superior and inferior parietal lobules, the temporal lobe, and the cerebellum posterior lobes. Furthermore, the FC between the left PFt and the left IPL exhibited a significantly positive correlation with age, and the FC between the left PFt and the right postcentral gyrus exhibited a significantly negative correlation with age. In addition, the FC between the right PFt and the right putamen exhibited a significantly negative correlation with age. Our findings suggest that the PFt area-based network develops and is reorganized with age.

Face Detection and the Development of Own-Species Bias in Infant Macaques

In visually complex environments, numerous items compete for attention. Infants may exhibit attentional efficiency-privileged detection, attention capture, and holding-for face-like stimuli. However, it remains unknown when these biases develop and what role, if any, experience plays in this emerging skill. Here, nursery-reared infant macaques' (Macaca mulatta; n = 10) attention to faces in 10-item arrays of nonfaces was measured using eye tracking. With limited face experience, 3-week-old monkeys were more likely to detect faces and looked longer at faces compared to nonfaces, suggesting a robust face detection system. By 3 months, after peer exposure, infants looked faster to conspecific faces but not heterospecific faces, suggesting an own-species bias in face attention capture, consistent with perceptual attunement.

The functional architecture of mother-infant communication, and the development of infant social expressiveness in the first two months

By two-three months, infants show active social expressions during face-to-face interactions. These interactions are important, as they provide the foundation for later emotional regulation and cognition, but little is known about how infant social expressiveness develops. We considered two different accounts. One emphasizes the contingency of parental responsiveness, regardless of its form; the other, the functional architecture account, emphasizes the preparedness of both infants and parents to respond in specific ways to particular forms of behaviour in their partner. We videotaped mother-infant interactions from one to nine weeks, and analysed them with a micro-analytic coding scheme. Infant social expressiveness increased through the nine-week period, particularly after 3 weeks. This development was unrelated to the extent of maternal contingent responsiveness, even to infant social expressions. By contrast, specific forms of response that mothers used preferentially for infant social expressions-mirroring, marking with a smile- predicted the increase in these infant behaviours over time. These results support a functional architecture account of the perceptual and behavioural predispositions of infants and parents that allow young infants to capitalize on relatively limited exposure to specific parental behaviours, in order to develop important social capacities.

Can newborn infants imitate?

For several decades, scientists have held that newborn human infants can imitate adult behaviors like mouth opening, tongue protruding, and finger movements. This has been difficult to explain. In particular, it is not clear how newborn infants could know enough about their own bodies and movements, and how these map onto the bodies and movements of others, to be able to match their own felt movements to the seen movements of others. Prominent theories posit the existence of inborn mechanisms that automatically link visual input from the movements of others to the infant's already existing motor programs to produce the same movements. Such mechanisms would be instances of the inheritance of specific knowledge. In this review, we explain how current data argue against the existence of an inborn mechanism for linking seen actions with programs for performing those actions. We then sketch an alternative, multicausal explanation for the gradual development of imitation across infancy and beyond. WIREs Cogn Sci 2017, 8:e1410. doi: 10.1002/wcs.1410 For further resources related to this article, please visit the WIREs website.

Mirror neurons in the tree of life: mosaic evolution, plasticity and exaptation of sensorimotor matching responses

Considering the properties of mirror neurons (MNs) in terms of development and phylogeny, we offer a novel, unifying, and testable account of their evolution according to the available data and try to unify apparently discordant research, including the plasticity of MNs during development, their adaptive value and their phylogenetic relationships and continuity. We hypothesize that the MN system reflects a set of interrelated traits, each with an independent natural history due to unique selective pressures, and propose that there are at least three evolutionarily significant trends that gave raise to three subtypes: hand visuomotor, mouth visuomotor, and audio-vocal. Specifically, we put forward a mosaic evolution hypothesis, which posits that different types of MNs may have evolved at different rates within and among species. This evolutionary hypothesis represents an alternative to both adaptationist and associative models. Finally, the review offers a strong heuristic potential in predicting the circumstances under which specific variations and properties of MNs are expected. Such predictive value is critical to test new hypotheses about MN activity and its plastic changes, depending on the species, the neuroanatomical substrates, and the ecological niche.

Embrained drives to perform extraordinary roles predict schizotypal traits in the general population

Some personal drives correspond to extraordinary social roles. Given that behavioral strategies associated with such drives may conflict with those associated with ordinary roles, they could cause behavioral disorganization. To test whether they do so independent of the factors responsible for full-blown schizotypy and schizophrenia, these drives were assessed in the general population. Two hundred and nine healthy volunteers were individually presented with hundreds of names of social roles in experimental psychology conditions. The task of the participant was to decide whether or not (s)he would consider performing the role at any moment of his/her life. Schizotypal traits were measured with the schizotypal personality questionnaire (SPQ), and delusion-like ideations were assessed by the Peters et al. Delusion Inventory. Demographics and social desirability were controlled for. Participants accepting a greater percentage of extraordinary roles had higher SPQ scores. Among the three factors of the SPQ, disorganization was the one best predicted by those percentages. This correlation (r=0.40, P=7.2E−09) was significantly greater (Fisher Z-transform, P=0.003) than the correlation between the percentages of ordinary roles accepted and the SPQ scores (r=0.145, P=0.044). Reaction times revealed no suboptimal cognitive functioning in high accepters of extraordinary roles and further strengthened the drive hypothesis. Their acceptances of roles were done faster and their rejections took longer than those of low accepters (P=5E−12). Culturally embrained drives to do extraordinary roles could thus be an independent factor of the symptoms measured in the normality to schizophrenia continuum.

Homo imitans? Seven reasons why imitation couldn't possibly be associative

Many comparative and developmental psychologists believe that we are Homo imitans; humans are more skilled and prolific imitators than other animals, because we have a special, inborn 'intermodal matching' mechanism that integrates representations of others with representations of the self. In contrast, the associative sequence learning (ASL) model suggests that human infants learn to imitate using mechanisms that they share with other animals, and the rich resources provided by their sociocultural environments. This article answers seven objections to the ASL model: (i) it presents evidence that newborns do not imitate; (ii) argues that infants receive a plentiful supply of the kind of experience necessary for learning to imitate; (iii) suggests that neither infants nor adults can imitate elementally novel actions; (iv) explains why non-human animals have a limited capacity for imitation; (v) discusses the goal-directedness of imitation; (vi) presents evidence that improvement in imitation depends on visual feedback; and (vii) reflects on the view that associative theories steal 'the soul of imitation'. The empirical success of the ASL model indicates that the mechanisms which make imitation possible, by aligning representations of self with representations of others, have been tweaked by cultural evolution, not built from scratch by genetic evolution.

Behavioral and TMS Markers of Action Observation Might Reflect Distinct Neuronal Processes

Transcranial magnetic stimulation (TMS) studies have shown that observing an action induces muscle-specific changes in corticospinal excitability. From a signal detection theory standpoint, this pattern can be related to sensitivity, which here would measure the capacity to distinguish between two action observation conditions. In parallel to these TMS studies, action observation has also been linked to behavioral effects such as motor priming and interference. It has been hypothesized that behavioral markers of action observation could be related to TMS markers and thus represent a potentially cost-effective mean of assessing the functioning of the action-perception system. However, very few studies have looked at possible relationships between these two measures. The aim of this study was to investigate if individual differences in sensitivity to action observation could be related to the behavioral motor priming and interference effects produced by action observation. To this end, 14 healthy participants observed index and little finger movements during a TMS task and a stimulus-response compatibility task. Index muscle displayed sensitivity to action observation, and action observation resulted in significant motor priming+interference, while no significant effect was observed for the little finger in both task. Nevertheless, our results indicate that the sensitivity measured in TMS was not related to the behavioral changes measured in the stimulus-response compatibility task. Contrary to a widespread assumption, the current results indicate that individual differences in physiological and behavioral markers of action observation may be unrelated. This could have important impacts on the potential use of behavioral markers in place of more costly physiological markers of action observation in clinical settings.

What's Special about Human Imitation? A Comparison with Enculturated Apes

What, if anything, is special about human imitation? An evaluation of enculturated apes’ imitation skills, a “best case scenario” of non-human apes’ imitation performance, reveals important similarities and differences between this special population of apes and human children. Candidates for shared imitation mechanisms include the ability to imitate various familiar transitive responses and object–object actions that involve familiar tools. Candidates for uniquely derived imitation mechanisms include: imitating novel transitive actions and novel tool-using responses as well as imitating opaque or intransitive gestures, regardless of familiarity. While the evidence demonstrates that enculturated apes outperform non-enculturated apes and perform more like human children, all apes, regardless of rearing history, generally excel at imitating familiar, over-rehearsed responses and are poor, relative to human children, at imitating novel, opaque or intransitive responses. Given the similarities between the sensory and motor systems of preschool age human children and non-human apes, it is unlikely that differences in sensory input and/or motor-output alone explain the observed discontinuities in imitation performance. The special rearing history of enculturated apes—including imitation-specific training—further diminishes arguments suggesting that differences are experience-dependent. Here, it is argued that such differences are best explained by distinct, specialized mechanisms that have evolved for copying rules and responses in particular content domains. Uniquely derived social and imitation learning mechanisms may represent adaptations for learning novel communicative gestures and complex tool-use. Given our species’ dependence on both language and tools, mechanisms that accelerated learning in these domains are likely to have faced intense selective pressures, starting with the earliest of human ancestors.

Neonatal face-to-face interactions promote later social behaviour in infant rhesus monkeys

In primates, including humans, mothers engage in face-to-face interactions with their infants, with frequencies varying both within and across species. However, the impact of this variation in face-to-face interactions on infant social development is unclear. Here we report that infant monkeys (Macaca mulatta) who engaged in more neonatal face-to-face interactions with mothers have increased social interactions at 2 and 5 months. In a controlled experiment, we show that this effect is not due to physical contact alone: monkeys randomly assigned to receive additional neonatal face-to-face interactions (mutual gaze and intermittent lip-smacking) with human caregivers display increased social interest at 2 months, compared with monkeys who received only additional handling. These studies suggest that face-to-face interactions from birth promote young primate social interest and competency.

Copying the development: mirror neurons in child development

Since intrauterine life, our brain is exposed to diverse internal and external factors that generate epigenetic changes affecting the neural networks and thus modifying the properties of the mirror neurons of the developing infant. We consider that changes on the mirror neurons may play a role on the neuro-developmental pathologies of an infant where no structural brain lesion is observed.

Walk like me, talk like me. The connection between mirror neurons and autism spectrum disorder

Understanding social cognition has become a hallmark in deciphering autism spectrum disorder. Neurobiological theories are taking precedence in causation studies as researchers look to abnormalities in brain development as the cause of deficits in social behavior, cognitive processes, and language. Following their discovery in the 1990s, mirror neurons have become a dominant theory for that the mirror neuron system may play a critical role in the pathophysiology of various symptoms of autism. Over the decades, the theory has evolved from the suggestion of a broken mirror neuron system to impairments in mirror neuron circuitry. The mirror neuron system has not gained total support due to inconsistent findings; a comprehensive analysis of the growing body of research could shed light on the benefits, or the disadvantage of continuing to study mirror neurons and their connection to autism.

Ultrasonographic Investigation of Human Fetus Responses to Maternal Communicative and Non-communicative Stimuli

During pregnancy fetuses are responsive to the external environment, specifically to maternal stimulation. During this period, brain circuits develop to prepare neonates to respond appropriately. The detailed behavioral analysis of fetus’ mouth movements in response to mothers’ speech may reveal important aspects of their sensorimotor and affective skills; however, to date, no studies have investigated this response. Given that newborns at birth are capable of responding with matched behaviors to the social signals emitted by the caregiver, we hypothesize that such precocious responses could emerge in the prenatal period by exploiting infants’ sensitivity to their mother’s voice. By means of a two-dimensional (2D) ultrasonography, we assessed whether fetuses at 25 weeks of gestation, showed a congruent mouthmotor response to maternal acoustic stimulation. Mothers were asked to provide different stimuli, each characterized by a different acoustic output (e.g., chewing, yawning, nursery rhymes, etc.) and we recorded the behavioral responses of 29 fetuses. We found that, when mothers sang the syllable LA in a nursery rhyme, fetuses significantly increased mouth openings. Other stimuli provided by the mother did not produce other significant changes in fetus’ behavior. This finding suggests that fetuses are sensitive only to specific maternal vocalizations (LA) and that fetal matched responses are rudimentary signs of early mirroring behaviors that become functional in the postnatal period. In conclusion, fetuses seem to be predisposed to respond selectively to specific maternal stimuli. We propose that such responses may play a role in the development of behavioral and emotional attunement with their mothers long before birth.

MOMENTS OF MEETING: THE RELEVANCE OF LOU SANDER'S AND DAN STERN'S CONCEPTUAL FRAMEWORK FOR UNDERSTANDING THE DEVELOPMENT OF PATHOLOGICAL SOCIAL RELATEDNESS

Lou Sander and Dan Stern made seminal contributions to our understanding of early child development, particularly in regard to the moment-to-moment intersubjective exchanges and mutual sensitivity that are at the core of the caregiver-infant relationship. Although their own studies focused primarily on the ways in which children's intersubjective experiences of mutual attunement lead to adaptive social relatedness and validate a healthy sense of self, this article focuses on the applicability of their theoretical conceptions to the development of pathological social relations. It explores the premise that the emotional validation derived from recurrent intersubjective experiences of mutual attunement involving negative affects can be as emotionally compelling from the child's standpoint as that derived from positive exchanges. Children's needs to recreate unhealthy, but affectively meaningful, moments with their caregivers can lead to ingrained, automatically operating pathological patterns of social behavior and affective expression that can take on a life of their own and strongly shape the child's subsequent socioemotional functioning. Following an overview of Sander's and Stern's conceptual thinking, developmental research and clinical case material will be utilized to illustrate how their work can enrich our understanding of developmental processes that can contribute to a number of emotion-specific, early relational disturbances.

Neonatal imitation and early social experience predict gaze following abilities in infant monkeys

Individuals vary in their social skills and motivation, the causes of which remain largely unknown. Here we investigated whether an individual’s propensity to interact with others measured within days after birth, and differences in infants’ early social environment, may predict a later social skill. Specifically, we tested whether neonatal imitation—newborns’ capacity to match modelled actions—and social experience in the first months of life predict gaze following (directing attention to locations where others look), in infant macaques (Macaca mulatta; n = 119). Facial gesture imitation in the first week of life predicted gaze following at 7 months of age. Imitators were better at gaze following than non-imitators, suggesting neonatal imitation may be an early marker predicting socio-cognitive functioning. In addition, infants with rich social environments outperformed infants with less socialization, suggesting early social experiences also support the development of infants’ gaze following competence. The present study offers compelling evidence that an individual difference present from birth predicts a functional social cognitive skill in later infancy. In addition, this foundational skill—gaze following—is plastic, and can be improved through social interactions, providing infants with a strong foundation for later social interaction and learning.

Experience-independent sex differences in newborn macaques: Females are more social than males

Human females exhibit greater social interest and skills relative to males, appearing in infancy, suggesting biological roots; however, male and female infants may be treated differently, potentially causing or amplifying sex differences. Here, we tested whether sex differences in social motivation emerge in infant monkeys (n = 48) reared in a controlled postnatal environment. Compared to males, females at 2-3 weeks looked more at conspecifics' faces (d = 0.65), especially the eyes (d = 1.09), and at 4-5 weeks exhibited more affiliative behaviors (d = 0.64), including gesturing, looking, and proximity to familiar and unfamiliar human caretakers. In sum, converging evidence from humans and monkeys suggests that female infants are more social than males in the first weeks of life, and that such differences may arise independent of postnatal experience. Individual differences in social interest have wide-ranging developmental consequences, impacting infants' social interaction quality and opportunities for learning. Understanding the evolution of sex differences and their developmental emergence is necessary to best support infants with varying levels of sociality.

Sensorized graspable devices for the study of motor imitation in infants

Researches regarding neonatal imitation are of great clinical interest since they can provide evidences of an innate mechanism underlying action understanding; the study can be led through the analysis of infants' spontaneous movements, like grasping, that are recognized as markers of neural activity. To this aim, a portable and non-intrusive device has been designed and developed to measure infants' grasping during the presentation of specific visual stimuli. The device is composed of two soft handles with embedded pressure sensors. During trials action observation should produce an increase of the measured pressure exerted by the infant's hand, according to the imitation-based paradigm of the defined clinical protocol. The final prototype has been tested within a pilot study and it has been proved to be suitable for monitoring infants' imitation abilities, meeting all the clinical specifications in terms of size, weight, safety and sensitivity. Preliminary acquired results are a starting point to clarify mechanisms related to imitation and sensorimotor system growth. The present methodology could be employed to boosts investigation on the development of mirror neurons in infants.

Observation and imitation of actions performed by humans, androids, and robots: an EMG study

Understanding others' actions is essential for functioning in the physical and social world. In the past two decades research has shown that action perception involves the motor system, supporting theories that we understand others' behavior via embodied motor simulation. Recently, empirical approach to action perception has been facilitated by using well-controlled artificial stimuli, such as robots. One broad question this approach can address is what aspects of similarity between the observer and the observed agent facilitate motor simulation. Since humans have evolved among other humans and animals, using artificial stimuli such as robots allows us to probe whether our social perceptual systems are specifically tuned to process other biological entities. In this study, we used humanoid robots with different degrees of human-likeness in appearance and motion along with electromyography (EMG) to measure muscle activity in participants' arms while they either observed or imitated videos of three agents produce actions with their right arm. The agents were a Human (biological appearance and motion), a Robot (mechanical appearance and motion), and an Android (biological appearance and mechanical motion). Right arm muscle activity increased when participants imitated all agents. Increased muscle activation was found also in the stationary arm both during imitation and observation. Furthermore, muscle activity was sensitive to motion dynamics: activity was significantly stronger for imitation of the human than both mechanical agents. There was also a relationship between the dynamics of the muscle activity and motion dynamics in stimuli. Overall our data indicate that motor simulation is not limited to observation and imitation of agents with a biological appearance, but is also found for robots. However we also found sensitivity to human motion in the EMG responses. Combining data from multiple methods allows us to obtain a more complete picture of action understanding and the underlying neural computations.

Early Social Experience Affects Neural Activity to Affiliative Facial Gestures in Newborn Nonhuman Primates

A fundamental issue in cognitive neuroscience is how the brain encodes the actions and intentions of others. The discovery of an action-production-perception mechanism underpinning such a capacity advanced our knowledge of how these processes occur; however, no study has examined how the early postnatal environment may shape action-production-perception. Here, we examined the effects of social experience on action-production-perception in 3-day-old rhesus macaques that were raised either with or without their biological mothers. We measured the neonatal imitation skills and brain electrical activity responses, while infants produced and observed facial gestures. We hypothesized that early social experiences may shape brain activity, as assessed via electroencephalogram suppression in the α band (5-7 Hz in infants, known as the mu rhythm) during action observation, and lead to more proficient imitation skills. Consistent with this hypothesis, the infants reared by their mothers were more likely to imitate lipsmacking (LS) - a natural, affiliative gesture - and exhibited greater mu rhythm desynchronization while viewing LS gestures than the nursery-reared infants. These effects were not found in response to tongue protrusion, a meaningless gesture, or a nonsocial control. These data suggest that socially enriched early experiences in the first days after birth increase brain sensitivity to socially relevant actions. © 2015 S. Karger AG, Basel.

Baby steps: investigating the development of perceptual-motor couplings in infancy

There are cells in our motor cortex that fire both when we perform and when we observe similar actions. It has been suggested that these perceptual-motor couplings in the brain develop through associative learning during correlated sensorimotor experience. Although studies with adult participants have provided support for this hypothesis, there is no direct evidence that associative learning also underlies the initial formation of perceptual-motor couplings in the developing brain. With the present study we addressed this question by manipulating infants' opportunities to associate the visual and motor representation of a novel action, and by investigating how this influenced their sensorimotor cortex activation when they observed this action performed by others. Pre-walking 7-9-month-old infants performed stepping movements on an infant treadmill while they either observed their own real-time leg movements (Contingent group) or the previously recorded leg movements of another infant (Non-contingent control group). Infants in a second control group did not perform any steps and only received visual experience with the stepping actions. Before and after the training period we measured infants' sensorimotor alpha suppression, as an index of sensorimotor cortex activation, while they watched videos of other infants' stepping actions. While we did not find greater sensorimotor alpha suppression following training in the Contingent group as a whole, we nevertheless found that the strength of the visuomotor contingency experienced during training predicted the amount of sensorimotor alpha suppression at post-test in this group. We did not find any effects of motor experience alone. These results suggest that the development of perceptual-motor couplings in the infant brain is likely to be supported by associative learning during correlated visuomotor experience.

The intrahemispheric functional properties of the developing sensorimotor cortex are influenced by maturation

The investigation of the functional changes in the sensorimotor cortex has important clinical implications as deviations from normal development can anticipate developmental disorders. The functional properties of the sensorimotor cortex can be characterized through the rolandic mu rhythm, already present during infancy. However, how the sensorimotor network develops from early infancy to adulthood, and how sensorimotor processing contributes to the generation of perceptual-motor coupling remains largely unknown. Here, we analyzed magnetoencephalographic (MEG) data recorded in two groups of infants (11-24 and 26-47 weeks), two groups of children (24-34 and 36-60 months), and a control group of adults (20-39 years), during intermixed conditions of rest and prehension. The MEG sensor array was positioned over the sensorimotor cortex of the contralateral hemisphere. We characterized functional connectivity and topological properties of the sensorimotor network across ages and conditions through synchronization likelihood and segregation/integration measures in an individual mu rhythm frequency range. All functional measures remained almost unchanged during the first year of life, whereas they varied afterwards through childhood to reach adult values, demonstrating an increase of both segregation and integration properties. With age, the sensorimotor network evolved from a more random (infants) to a "small-world" organization (children and adults), more efficient both locally and globally. These findings are in line with prior studies on structural and functional brain development in infants, children and adults. We could not demonstrate any significant change in the functional properties of the sensorimotor cortex in the prehension condition with respect to rest. Our results support the view that, since early infancy, the functional properties of the developing sensorimotor cortex are modulated by maturation.

Inhaled oxytocin increases positive social behaviors in newborn macaques

Early caregiver-infant interactions are critical for infants' socioemotional and cognitive development. Several hormones and neuromodulators, including oxytocin, affect these interactions. Exogenous oxytocin promotes social behaviors in several species, including human and nonhuman primates. Although exogenous oxytocin increases social function in adults--including expression recognition and affiliation--it is unknown whether oxytocin can increase social interactions in infants. We hypothesized that nebulized oxytocin would increase affiliative social behaviors and such effects would be modulated by infants' social skills, measured earlier in development. We also hypothesized that oxytocin's effects on social behaviors may be due to its anxiolytic effects. We tested these hypotheses in a blind study by nebulizing 7- to 14-d-old macaques (n = 28) with oxytocin or saline. Following oxytocin administration, infants' facial gesturing at a human caregiver increased, and infants' salivary oxytocin was positively correlated with the time spent in close proximity to a caregiver. Infants' imitative skill (measured earlier in development: 1-7 d of age) predicted oxytocin-associated increases in affiliative behaviors--lip smacking, visual attention to a caregiver, and time in close proximity to a caregiver--suggesting that infants with higher propensities for positive social interactions are more sensitive to exogenous oxytocin. Oxytocin also decreased salivary cortisol, but not stress-related behaviors (e.g., scratching), suggesting the possibility of some anxiolytic effects. To our knowledge, this study provides the first evidence that oxytocin increases positive social behaviors in newborns. This information is of critical importance for potential interventions aimed at ameliorating inadequate social behaviors in infants with higher likelihood of developing neurodevelopmental disorder.