You'll never crawl alone: Neurophysiological evidence for experience-dependent motor resonance in infancy

Flexibility in embodied language understanding

Do people use sensori-motor cortices to understand language? Here we review neurocognitive studies of language comprehension in healthy adults and evaluate their possible contributions to theories of language in the brain. We start by sketching the minimal predictions that an embodied theory of language understanding makes for empirical research, and then survey studies that have been offered as evidence for embodied semantic representations. We explore four debated issues: first, does activation of sensori-motor cortices during action language understanding imply that action semantics relies on mirror neurons? Second, what is the evidence that activity in sensori-motor cortices plays a functional role in understanding language? Third, to what extent do responses in perceptual and motor areas depend on the linguistic and extra-linguistic context? And finally, can embodied theories accommodate language about abstract concepts? Based on the available evidence, we conclude that sensori-motor cortices are activated during a variety of language comprehension tasks, for both concrete and abstract language. Yet, this activity depends on the context in which perception and action words are encountered. Although modality-specific cortical activity is not a sine qua non of language processing even for language about perception and action, sensori-motor regions of the brain appear to make functional contributions to the construction of meaning, and should therefore be incorporated into models of the neurocognitive architecture of language.

How learning to shake a rattle affects 8-month-old infants' perception of the rattle's sound: electrophysiological evidence for action-effect binding in infancy

Bidirectional action-effect associations play a fundamental role in intentional action control and the development of the mirror neuron system. However, it has been questioned if infants are able to acquire bidirectional action-effect associations (i.e., are able to intentionally control their actions). To investigate this, we trained 8-month-old infants for one week to use a novel rattle that produced a specific sound when shaken. Infants were also presented with another sound, which was not related to an action. Thereafter, infants' EEG responses to these two sounds and to an additional, unfamiliar sound were recorded. Infants displayed a stronger mu-desynchronization above cortical motor sites (i.e., motor resonance) when listening to the action-related sound than when hearing other sounds. Our results provide therefore electrophysiological evidence that infants as young as 8 months are able to acquire bidirectional action-effect associations and parallel findings of audiovisual mirror neurons in the monkey brain.

Neural correlates of action observation and execution in 14-month-old infants: an event-related EEG desynchronization study

There is increasing interest in neurobiological methods for investigating the shared representation of action perception and production in early development. We explored the extent and regional specificity of EEG desynchronization in the infant alpha frequency range (6-9 Hz) during action observation and execution in 14-month-old infants. Desynchronization during execution was restricted to central electrode sites, while action observation was associated with a broader desynchronization across frontal, central, and parietal regions. The finding of regional specificity in the overlap between EEG responses to action execution and observation suggests that the rhythm seen in the 6-9 Hz range over central sites in infancy shares certain properties with the adult mu rhythm. The magnitude of EEG desynchronization to action perception and production appears to be smaller for infants than for adults and older children, suggesting developmental change in this measure.

Joint action modulates motor system involvement during action observation in 3-year-olds

When we are engaged in a joint action, we need to integrate our partner’s actions with our own actions. Previous research has shown that in adults the involvement of one’s own motor system is enhanced during observation of an action partner as compared to during observation of an individual actor. The aim of this study was to investigate whether similar motor system involvement is present at early stages of joint action development and whether it is related to joint action performance. In an EEG experiment with 3-year-old children, we assessed the children’s brain activity and performance during a joint game with an adult experimenter. We used a simple button-pressing game in which the two players acted in turns. Power in the mu- and beta-frequency bands was compared when children were not actively moving but observing the experimenter’s actions when (1) they were engaged in the joint action game and (2) when they were not engaged. Enhanced motor involvement during action observation as indicated by attenuated sensorimotor mu- and beta-power was found when the 3-year-olds were engaged in the joint action. This enhanced motor activation during action observation was associated with better joint action performance. The findings suggest that already in early childhood the motor system is differentially activated during action observation depending on the involvement in a joint action. This motor system involvement might play an important role for children’s joint action performance.

Neural correlates of dyadic interaction during infancy

This study examines the electrophysiological correlates of dyadic interaction in 14-month-old infants. Infants were presented with three conditions of live stimuli. A baseline condition involved the observation of moving geometric shapes. In a second condition the infant observed an adult performing movements that were not in reference to the infant and were not within the infant's proficient motor repertoire, such as dancing or hopping. A third condition involved face to face dyadic interactions in the context of an imitative game, where the infant and adult engaged in copying each other's hand and facial actions. Motor activity by the infant was controlled between conditions by synchronizing EEG with video frames of action. Infant EEG data was then edited offline to match in motor intensity across conditions. We expected mu rhythm (6-9 Hz) suppression during dyadic interactions relative to the amount of mu present in the baseline condition. This prediction was confirmed. We also observed suppressed mu in the interaction condition relative to the observation condition. The mu rhythm results suggest that infants at 14 months may well utilize a functioning mirroring system during dyadic interactions.

Trajectory recognition as the basis for object individuation: a functional model of object file instantiation and object-token encoding

The perception of persisting visual objects is mediated by transient intermediate representations, object files, that are instantiated in response to some, but not all, visual trajectories. The standard object file concept does not, however, provide a mechanism sufficient to account for all experimental data on visual object persistence, object tracking, and the ability to perceive spatially disconnected stimuli as continuously existing objects. Based on relevant anatomical, functional, and developmental data, a functional model is constructed that bases visual object individuation on the recognition of temporal sequences of apparent center-of-mass positions that are specifically identified as trajectories by dedicated "trajectory recognition networks" downstream of the medial-temporal motion-detection area. This model is shown to account for a wide range of data, and to generate a variety of testable predictions. Individual differences in the recognition, abstraction, and encoding of trajectory information are expected to generate distinct object persistence judgments and object recognition abilities. Dominance of trajectory information over feature information in stored object tokens during early infancy, in particular, is expected to disrupt the ability to re-identify human and other individuals across perceptual episodes, and lead to developmental outcomes with characteristics of autism spectrum disorders.

Is the good-imitator-poor-talker profile syndrome-specific in Down syndrome?: evidence from standardised imitation and language measures

The emergence of the Down syndrome (DS) behavioural phenotype during early development may be of great importance for early intervention. The main goal of this study was to investigate the good-imitator-poor-talker developmental profile in DS at preschool age. Twenty children with Down syndrome (DS; mean nonverbal mental age NMA 1 y10 m) and 15 children with non-specific mental retardation (NS-MR; mean NMA 1 y11 m) participated in this study. The Preschool Imitation and Praxis Scale (PIPS) and the Dutch version of the MacArthur-Bates Communicative Development Inventories (N-CDI) were used to determine absolute and relative (contrasted to a nonverbal mental age reference) imitation and language abilities. Results revealed that there was clear evidence for a good-imitator-poor-talker profile in preschoolers with DS. However, only the advanced bodily imitation ability seems to be syndrome-specific. Clinical implications of these findings are considered.

Observational learning of new movement sequences is reflected in fronto-parietal coherence

Mankind is unique in her ability for observational learning, i.e. the transmission of acquired knowledge and behavioral repertoire through observation of others' actions. In the present study we used electrophysiological measures to investigate brain mechanisms of observational learning. Analysis investigated the possible functional coupling between occipital (alpha) and motor (mu) rhythms operating in the 10 Hz frequency range for translating "seeing" into "doing". Subjects observed movement sequences consisting of six consecutive left or right hand button presses directed at one of two target-buttons for subsequent imitation. Each movement sequence was presented four times, intervened by short pause intervals for sequence rehearsal. During a control task subjects observed the same movement sequences without a requirement for subsequent reproduction. Although both alpha and mu rhythms desynchronized during the imitation task relative to the control task, modulations in alpha and mu power were found to be largely independent from each other over time, arguing against a functional coupling of alpha and mu generators during observational learning. This independence was furthermore reflected in the absence of coherence between occipital and motor electrodes overlaying alpha and mu generators. Instead, coherence analysis revealed a pair of symmetric fronto-parietal networks, one over the left and one over the right hemisphere, reflecting stronger coherence during observation of movements than during pauses. Individual differences in fronto-parietal coherence were furthermore found to predict imitation accuracy. The properties of these networks, i.e. their fronto-parietal distribution, their ipsilateral organization and their sensitivity to the observation of movements, match closely with the known properties of the mirror neuron system (MNS) as studied in the macaque brain. These results indicate a functional dissociation between higher order areas for observational learning (i.e. parts of the MNS as reflected in 10 Hz coherence measures) and peripheral structures (i.e. lateral occipital gyrus for alpha; central sulcus for mu) that provide low-level support for observation and motor imagery of action sequences.

Can 14- to 20-month-old children learn that a tool serves multiple purposes? A developmental study on children's action goal prediction

We investigated infants' visual anticipations to the target of an ongoing tool-use action and examined if infants can learn that tools serve multiple functions and can thus be used on different targets. Specifically, we addressed the question at what age children are able to predict the goal of an ongoing tool-use action on the basis of how the actor initiates the action. Fourteen- and 20-month-old children watched a model using a tool to execute two different actions. Each way of grasping and holding the tool was predictive for its use on a particular target. Analyses revealed that the 20- but not the 14-month-olds were able to visually anticipate to the correct target during action observation, which suggests that they perceived the initial part of the tool-use action as predictive for its use on an action target.

Teach to reach: the effects of active vs. passive reaching experiences on action and perception

Reaching is an important and early emerging motor skill that allows infants to interact with the physical and social world. However, few studies have considered how reaching experiences shape infants' own motor development and their perception of actions performed by others. In the current study, two groups of infants received daily parent guided play sessions over a 2-weeks training period. Using "Sticky Mittens", one group was enabled to independently pick up objects whereas the other group only passively observed their parent's actions on objects. Following training, infants' manual and visual exploration of objects, agents, and actions in a live and a televised context were assessed. Our results showed that only infants who experienced independent object apprehension advanced in their reaching behavior, and showed changes in their visual exploration of agents and objects in a live setting. Passive observation was not sufficient to change infants' behavior. To our surprise, the effects of the training did not seem to generalize to a televised observation context. Together, our results suggest that early motor training can jump-start infants' transition into reaching and inform their perception of others' actions.

Goal anticipation during action observation is influenced by synonymous action capabilities, a puzzling developmental study

Eighteen- and 25-month-old human toddlers' ability to manually solve a puzzle and their ability to anticipate the goal during observation of similar actions were investigated. Results demonstrate that goal anticipation during action observation is dependent on manual ability, both on a group level (only 25-month-olds solved the manual task and anticipated the goal during observation) and individually within the older age group (r (xy) = 0.53). These findings suggests a connection between manual ability and the ability to anticipate the goal of others' actions in toddlers, in accordance with the direct matching hypothesis.

Neurobiology of imitation

Recent research on the neurobiology of imitation has gone beyond the study of its 'core' mechanisms, focus of investigation of the past years.. The current trends can be grouped into four main categories: (1) non 'core' neural mechanisms that are also important for imitation; (2) mechanisms of control, in both imitative learning and inhibition of imitation; (3) the developmental trajectory of neural mechanisms of imitation and their relation with the development of social cognition; (4) neurobiological mechanisms of imitation in non-primates, in particular vocal learning in songbirds, and their relations with similar mechanisms of vocal learning in humans. The existing data suggest that both perceptual and motor aspects of imitation follow organizing principles that originally belonged to the motor system.

Predictive motor activation during action observation in human infants

Certain regions of the human brain are activated both during action execution and action observation. This so-called 'mirror neuron system' has been proposed to enable an observer to understand an action through a process of internal motor simulation. Although there has been much speculation about the existence of such a system from early in life, to date there is little direct evidence that young infants recruit brain areas involved in action production during action observation. To address this question, we identified the individual frequency range in which sensorimotor alpha-band activity was attenuated in nine-month-old infants' electroencephalographs (EEGs) during elicited reaching for objects, and measured whether activity in this frequency range was also modulated by observing others' actions. We found that observing a grasping action resulted in motor activation in the infant brain, but that this activity began prior to observation of the action, once it could be anticipated. These results demonstrate not only that infants, like adults, display overlapping neural activity during execution and observation of actions, but that this activation, rather than being directly induced by the visual input, is driven by infants' understanding of a forthcoming action. These results provide support for theories implicating the motor system in action prediction.