Does the end justify the means? A PET exploration of the mechanisms involved in human imitation

Are there dedicated neural mechanisms for imitation? A study of grist and mills

Are there brain regions that are specialized for the execution of imitative actions? We compared two hypotheses of imitation: the mirror neuron system (MNS) hypothesis predicts frontal and parietal engagement which is specific to imitation, while the Grist-Mills hypothesis predicts no difference in brain activation between imitative and matched non-imitative actions. Our delayed imitation fMRI paradigm included two tasks, one where correct performance was defined by a spatial rule and another where it was defined by an item-based rule. For each task, participants could learn a sequence from a video of a human hand performing the task, from a matched "Ghost" condition, or from text instructions. When participants executed actions after seeing the Hand demonstration (compared to Ghost and Text demonstrations), no activation differences occurred in frontal or parietal regions; rather, activation was localized primarily to occipital cortex. This adds to a growing body of evidence which indicates that imitation-specific responses during action execution do not occur in canonical mirror regions, contradicting the mirror neuron system hypothesis. However, activation differences did occur between action execution in the Hand and Ghost conditions outside MNS regions, which runs counter to the Grist-Mills hypothesis. We conclude that researchers should look beyond these hypotheses as well as classical MNS regions to describe the ways in which imitative actions are implemented by the brain.

Reaction time coupling in a joint stimulus-response task: A matter of functional actions or likable agents?

Shaping one owns actions by observing others’ actions is driven by the deep-rooted mechanism of perception-action coupling. It typically occurs automatically, expressed as for example the unintentional synchronization of reaction times in interactive games. Theories on perception-action coupling highlight its benefits such as the joint coordination of actions to cooperatively perform tasks properly, the learning of novel actions from others, and the bonding with likable others. However, such functional aspects and how they shape perception-action coupling have never been compared quantitatively. Here we tested a total of hundred-fifteen participants that played a stimulus-response task while, in parallel, they observed videos of agents that played the exact same task several milliseconds in advance. We compared to what degree the reaction times of actions of agents, who varied their behavior in terms of functionality and likability in preceding prisoner dilemma games and quizzes, shape the reaction times of human test participants. To manipulate functionality and likability, we varied the predictability of cooperative behavior and correctness of actions of agents, respectively, resulting in likable (cooperative), dislikable (uncooperative), functional (correct actions), and dysfunctional (incorrect actions) agents. The results of three experiments showed that the participants’ reaction times correlated most with the reaction times of agents that expressed functional behavior. However, the likability of agents had no effects on reaction time correlations. These findings suggest that, at least in the current computer task, participants are more likely to adopt the timing of actions from people that perform correct actions than from people that they like.

Adult Attachment Affects Neural Response to Preference-Inferring in Ambiguous Scenarios: Evidence From an fMRI Study

Humans are highly social animals, and the ability to cater to the preferences of other individuals is encouraged by society. Preference-inferring is an important aspect of the theory of mind (TOM). Many previous studies have shown that attachment style is closely related to TOM ability. However, little is known about the effects of adult attachment style on preferences inferring under different levels of certainty. Here, we investigated how adult attachment style affects neural activity underlying preferences inferred under different levels of certainty by using functional magnetic resonance imaging (fMRI). The fMRI results demonstrated that adult attachment influenced the activation of anterior insula (AI) and inferior parietal lobule (IPL) in response to ambiguous preference-inferring. More specifically, in the ambiguous preference condition, the avoidant attached groups exhibited a significantly enhanced activation than secure and anxious attached groups in left IPL; the anxious attached groups exhibited a significantly reduced activation secure attached group in left IPL. In addition, the anxious attached groups exhibited a significantly reduced activation than secure and avoidant attached groups in left AI. These results were also further confirmed by the subsequent PPI analysis. The results from current study suggest that, under ambiguous situations, the avoidant attached individuals show lower sensitivity to the preference of other individuals and need to invest more cognitive resources for preference-reasoning; while compared with avoidant attached group, the anxious attached individuals express high tolerance for uncertainty and a higher ToM proficiency. Results from the current study imply that differences in preference-inferring under ambiguous conditions associated with different levels of individual attachment may explain the differences in interpersonal interaction.

The Social Effect of "Being Imitated" in Children with Autism Spectrum Disorder

There is evidence that “being imitated” has social effects, and that the imitation of the child's actions may be used as a strategy to promote social engagement in children with autism spectrum disorder (ASD). The observation of someone that imitates us recruits, indeed, neural areas involved in social cognition. We reviewed studies exploring the behavioral consequences of “being imitated” in children with ASD. We aimed at assessing what are the social skills targeted by this strategy, and the factors that may improve the response. The “being imitated” strategy improves social gazes, proximal social behaviors, and play skills, particularly in children with low developmental level, and also when the strategy is implemented by children's mothers. The “being imitated” may be used as a tool in early intervention to improve social skills, helping to assess the effects of intervention at both behavioral and neural level.

Syntax in Action Has Priority over Movement Selection in Piano Playing: An ERP Study

Complex human behavior is hierarchically organized. Whether or not syntax plays a role in this organization is currently under debate. The present ERP study uses piano performance to isolate syntactic operations in action planning and to demonstrate their priority over nonsyntactic levels of movement selection. Expert pianists were asked to execute chord progressions on a mute keyboard by copying the posture of a performing model hand shown in sequences of photos. We manipulated the final chord of each sequence in terms of Syntax (congruent/incongruent keys) and Manner (conventional/unconventional fingering), as well as the strength of its predictability by varying the length of the Context (five-chord/two-chord progressions). The production of syntactically incongruent compared to congruent chords showed a response delay that was larger in the long compared to the short context. This behavioral effect was accompanied by a centroparietal negativity in the long but not in the short context, suggesting that a syntax-based motor plan was prepared ahead. Conversely, the execution of the unconventional manner was not delayed as a function of Context and elicited an opposite electrophysiological pattern (a posterior positivity). The current data support the hypothesis that motor plans operate at the level of musical syntax and are incrementally translated to lower levels of movement selection.

The panoply of field-dependent behavior in 1436 stroke patients. The mirror neuron system uncoupled and the consequences of loss of personal autonomy

Evaluation of the multifaceted nature of frontal network syndromes is uniquely challenging and rarely tested in the acute/sub-acute stroke period. Field-dependent behavior such as imitation behavior, utilization behavior, and environmental dependency syndrome, as a component of altered environmental autonomy, may be a reliable bedside test. This research focused on the frequency of field-dependent behavior in stroke, the subtypes and relation to frontal lobe lesion location and stroke etiology. A validated frontal network score incorporating a 10-point imitation behavior scale was applied to alert patients without significant aphasia, encephalopathy, dementia, or substance abuse. Discriminative validity assessment with magnetic resonance imaging, diffusion weight imaging (MRI-DWI brain) was performed and correlational validity was established using standard neuropsychological tests. Of the stroke patients (n = 1436), those with frontal network symptoms (335/1203; 28%) were analyzed further. In the 73 patients with lesions restricted to the frontal lobes or the frontal subcortical circuits, 56 complied with the 10-point imitation behavior scale testing. Forty-five of 56 (80%) demonstrated imitation behavior (sensitivity 73% and specificity 94%). Correlational validity testing with four commonly used frontal lobe neuropsychological tests was good. The stroke etiology included 26 (59%) "other" causes, 9 (20%) intracerebral hemorrhages, 3 (7%) cardioembolic causes, 3 (7%) large vessel disease, 2 (4%) small vessel disease, and 2 (4%) unknown etiology. Field-dependent behaviour subtypes included imitation behavior (n = 45), utilization behavior (n = 9), environmental dependency syndrome (n = 4), and complex other forms of environmental dependence syndrome (n = 5). It was concluded that imitation behavior is a relatively common occurrence with lesions in the frontal lobes in the acute/sub-acute stroke period and is associated predominantly with non-mainstream (other) stroke causes and intracerebral hemorrhage.

Imitation of an action course in preschool and school-aged children: a hierarchical reconstruction

Imitation is commonly considered as a hierarchical process. The current study explored the reproduction of a multi-task course in deferred imitation. Eighty-five children between 3.5 and 7.5 years old were divided into five groups and instructed to watch a live human adult demonstrator who performed simple successive actions, such as walking, jumping, grasping, carrying objects from one location to another through six sessions. After a five-minute delay, the children were individually instructed to reproduce the course. Their responses were videotaped and coded in dichotomous data at two hierarchical levels, namely goals and their spatial location. The main findings showed no improvement in the replication of goals due either to age or trials. However, there was an improvement in the integration of the goals' spatial location over trials. This signifies that imitation is an active reconstruction mechanism hierarchically organized.

Neural mirroring systems: exploring the EEG μ rhythm in human infancy

How do human children come to understand the actions of other people? What neural systems are associated with the processing of others' actions and how do these systems develop, starting in infancy? These questions span cognitive psychology and developmental cognitive neuroscience, and addressing them has important implications for the study of social cognition. A large amount of research has used behavioral measures to investigate infants' imitation of the actions of other people; a related but smaller literature has begun to use neurobiological measures to study of infants' action representation. Here we focus on experiments employing electroencephalographic (EEG) techniques for assessing mu rhythm desynchronization in infancy, and analyze how this work illuminates the links between action perception and production prior to the onset of language.

Learning by observation: insights from Williams syndrome

Observing another person performing a complex action accelerates the observer’s acquisition of the same action and limits the time-consuming process of learning by trial and error. Observational learning makes an interesting and potentially important topic in the developmental domain, especially when disorders are considered. The implications of studies aimed at clarifying whether and how this form of learning is spared by pathology are manifold. We focused on a specific population with learning and intellectual disabilities, the individuals with Williams syndrome. The performance of twenty-eight individuals with Williams syndrome was compared with that of mental age- and gender-matched thirty-two typically developing children on tasks of learning of a visuo-motor sequence by observation or by trial and error. Regardless of the learning modality, acquiring the correct sequence involved three main phases: a detection phase, in which participants discovered the correct sequence and learned how to perform the task; an exercise phase, in which they reproduced the sequence until performance was error-free; an automatization phase, in which by repeating the error-free sequence they became accurate and speedy. Participants with Williams syndrome beneficiated of observational training (in which they observed an actor detecting the visuo-motor sequence) in the detection phase, while they performed worse than typically developing children in the exercise and automatization phases. Thus, by exploiting competencies learned by observation, individuals with Williams syndrome detected the visuo-motor sequence, putting into action the appropriate procedural strategies. Conversely, their impaired performances in the exercise phases appeared linked to impaired spatial working memory, while their deficits in automatization phases to deficits in processes increasing efficiency and speed of the response. Overall, observational experience was advantageous for acquiring competencies, since it primed subjects’ interest in the actions to be performed and functioned as a catalyst for executed action.

Observation-to-Imitate Plus Practice Could Add Little to Physical Therapy Benefits Within 31 Days of Stroke

Background and Purpose. Observation of action with intention-to-imitate (OTI) might enhance motor recovery. This early phase trial investigated whether OTI followed by physical practice (OTI + PP) enhanced the benefits of conventional physical therapy (CPT) on upper limb recovery early after stroke. Methods. Participants were 3 to 31 days poststroke. They had substantial paresis and ability to imitate action with their ipsilesional arm. After baseline measures, participants were randomized to either OTI + PP in addition to CPT or to CPT only. Outcome measures were made after 15 days of treatment. The measurement battery was the Motricity Index (MI) and the Action Research Arm Test (ARAT). Change, baseline to outcome, was examined using the Wilcoxon test for within group and Mann–Whitney U test for between groups. Results. Sixty-five of 570 stroke survivors were eligible, 55 were able to imitate, 37 gave informed consent, 7 were transferred out of area before baseline, and 29 were randomized. Outcome measures were completed with 13 CPT participants and 9 OTI + PP participants. Both groups showed statistically significant improvements for the MI (CPT median change 8, P = .003; OTI + PP median change 10, P = .012) but the median (95% confidence interval [CI]) between-group difference was 0.0 (−11, 16), P = 1.000. For the ARAT, only the CPT group showed a statistically significant improvement (median 9, P = .006). The median (95% CI) between-group difference of 1.0 (−18, 23) was not statistically significant ( P = .815). Conclusions. These findings suggest that OTI + PP might add little to the benefits of CPT early after stroke.

Stone tools, language and the brain in human evolution

Long-standing speculations and more recent hypotheses propose a variety of possible evolutionary connections between language, gesture and tool use. These arguments have received important new support from neuroscientific research on praxis, observational action understanding and vocal language demonstrating substantial functional/anatomical overlap between these behaviours. However, valid reasons for scepticism remain as well as substantial differences in detail between alternative evolutionary hypotheses. Here, we review the current status of alternative 'gestural' and 'technological' hypotheses of language origins, drawing on current evidence of the neural bases of speech and tool use generally, and on recent studies of the neural correlates of Palaeolithic technology specifically.

Multiple neural representations of object-directed action in an imitative context

Object-directed action consists of aspects that range from low-level kinematic patterns to high-level action goals. Although previous studies have suggested that the human mirror neuron system (MNS) is involved in understanding or imitating an observed action, it is unclear precisely which levels of action representation are reflected in MNS activity. In this study, we used an imitation-matching task, which is previously used in behavioral experiments for infants, and fMRI to reveal the neural basis for imitation of multiple representations of observed actions. In our experiment, two video footages showing a pen being grasped and placed into one of two cups were sequentially presented. The participants judged whether an actor's action in the first movie was correctly imitated by an imitator in the second movie, regarding the following four aspects: action goal, a means of manipulation, an effector used, and movement trajectory. Although identical sets of stimuli were presented, different brain regions were activated, depending on the matching judgments made by subjects between the two actions. The current study indicates that distinct brain regions are involved in recognition of multiple aspects of transitive actions, which is largely consistent with a visuomotor circuit of action production by the observer.

The role of the superior temporal sulcus and the mirror neuron system in imitation

It has been suggested that in humans the mirror neuron system provides a neural substrate for imitation behaviour, but the relative contributions of different brain regions to the imitation of manual actions is still a matter of debate. To investigate the role of the mirror neuron system in imitation we used fMRI to examine patterns of neural activity under four different conditions: passive observation of a pantomimed action (e.g., hammering a nail); (2) imitation of an observed action; (3) execution of an action in response to a word cue; and (4) self-selected execution of an action. A network of cortical areas, including the left supramarginal gyrus, left superior parietal lobule, left dorsal premotor area and bilateral superior temporal sulcus (STS), was significantly active across all four conditions. Crucially, within this network the STS bilaterally was the only region in which activity was significantly greater for action imitation than for the passive observation and execution conditions. We suggest that the role of the STS in imitation is not merely to passively register observed biological motion, but rather to actively represent visuomotor correspondences between one's own actions and the actions of others.

How instructions modify perception: an fMRI study investigating brain areas involved in attributing human agency

Behavioural studies suggest that the processing of movement stimuli is influenced by beliefs about the agency behind these actions. The current study examined how activity in social and action related brain areas differs when participants were instructed that identical movement stimuli were either human or computer generated. Participants viewed a series of point-light animation figures derived from motion-capture recordings of a moving actor, while functional magnetic resonance imaging (fMRI) was used to monitor patterns of neural activity. The stimuli were scrambled to produce a range of stimulus realism categories; furthermore, before each trial participants were told that they were about to view either a recording of human movement or a computer-simulated pattern of movement. Behavioural results suggested that agency instructions influenced participants' perceptions of the stimuli. The fMRI analysis indicated different functions within the paracingulate cortex: ventral paracingulate cortex was more active for human compared to computer agency instructed trials across all stimulus types, whereas dorsal paracingulate cortex was activated more highly in conflicting conditions (human instruction, low realism or vice versa). These findings support the hypothesis that ventral paracingulate encodes stimuli deemed to be of human origin, whereas dorsal paracingulate cortex is involved more in the ascertainment of human or intentional agency during the observation of ambiguous stimuli. Our results highlight the importance of prior instructions or beliefs on movement processing and the role of the paracingulate cortex in integrating prior knowledge with bottom-up stimuli.

Time-dependent lateralization of social learning in the domestic chick (Gallus gallus domesticus): Effects of retention delays in the observed lateralization pattern

Day-old chicks have been shown capable of learning to avoid pecking by observation only of a conspecific showing a disgust reaction after pecking a bitter-tasting bead. This learning is lateralized: access to the right hemisphere appears necessary for successful performance 30 min after training. This is in contrast to the non-social learning version of this learning task, in which the left hemisphere appears to play the dominant role, although both the left and right hemispheres are, in turn, subject to brief windows of "enhanced recall" during memory formation. In our present work we wished to investigate whether such recall events are also prevalent in the social learning task. We investigated 3 such windows; 25 min (a right hemisphere event), 32 min (left-hemisphere event) and 64 min (a possible left-hemisphere event following an interconnection of both hemispheres allowing memory transfer between the two hemispheres). At 32 and 64 min after training we found no evidence of functional lateralization. At 25 min, however, we found right hemisphere dominance. We suggest that a lateralization effect occurs in the social version of the PAL (passive avoidance learning) only at time points associated with right hemisphere dominance. It seems that lateralization is not able to emerge at time points where a left-hemisphere event is expected, because the two "lateralization effects" (right hemisphere dominance associated with the social task and left-hemisphere dominance associated with the PAL task) are in conflict.

Changes in cerebello-motor connectivity during procedural learning by actual execution and observation

The cerebellum is involved in motor learning of new procedures both during actual execution of a motor task and during observational training. These processes are thought to depend on the activity of a neural network that involves the lateral cerebellum and primary motor cortex (M1). In this study, we used a twin-coil TMS technique to investigate whether execution and observation of a visuomotor procedural learning task is related to modulation of cerebello-motor connectivity. We observed that, at rest, a magnetic conditioning pulse applied over the lateral cerebellum reduced the motor-evoked potentials obtained by stimulating the contralateral M1, indicating activation of a cerebello-motor connection. Furthermore, during procedural learning, cerebellar stimulation resulted in selective facilitation, not inhibition, of contralateral M1 excitability. The effects were evident when motor learning was obtained by actual execution of the task or by observation, but they disappeared if procedural learning had already been acquired by previous observational training. These results indicate that changes in cerebello-motor connectivity occur in relation to specific phases of procedural learning, demonstrating a complex pattern of excitatory and inhibitory drives modulated across time.

ALE meta-analysis of action observation and imitation in the human brain

Over the last decade, many neuroimaging studies have assessed the human brain networks underlying action observation and imitation using a variety of tasks and paradigms. Nevertheless, questions concerning which areas consistently contribute to these networks irrespective of the particular experimental design and how such processing may be lateralized remain unresolved. The current study aimed at identifying cortical areas consistently involved in action observation and imitation by combining activation likelihood estimation (ALE) meta-analysis with probabilistic cytoarchitectonic maps. Meta-analysis of 139 functional magnetic resonance and positron emission tomography experiments revealed a bilateral network for both action observation and imitation. Additional subanalyses for different effectors within each network revealed highly comparable activation patterns to the overall analyses on observation and imitation, respectively, indicating an independence of these findings from potential confounds. Conjunction analysis of action observation and imitation meta-analyses revealed a bilateral network within frontal premotor, parietal, and temporo-occipital cortex. The most consistently rostral inferior parietal area was PFt, providing evidence for a possible homology of this region to macaque area PF. The observation and imitation networks differed particularly with respect to the involvement of Broca's area: whereas both networks involved a caudo-dorsal part of BA 44, activation during observation was most consistent in a more rostro-dorsal location, i.e., dorsal BA 45, while activation during imitation was most consistent in a more ventro-caudal aspect, i.e., caudal BA 44. The present meta-analysis thus summarizes and amends previous descriptions of the human brain networks related to action observation and imitation.

Effect of information load and time on observational learning

We examined whether altering the amount of and moment when visual information is presented affected observational learning for participants practicing a bowling skill. On Day 1, four groups practiced a cricket bowling action. Three groups viewed a full-body point-light model, the model's bowling arm, or between-limb coordination of the model's left and right wrists only. Following retention tests on Day 2, all participants practiced after viewing a full-body display. Retention was again tested on Day 3. Bowling accuracy improved in all four practice groups. Kinematics of the bowling arm became more like the model for the full-body and intralimb groups only. All groups improved on measures of interlimb coordination. Visual search data indicated that participants mainly focused their gaze on the model's bowling arm. These data lead to the suggestion that viewing "end-effector" information (i.e., information pertaining to the bowling arm) is an important perceptual constraint early in observational learning. Implicit manipulations designed to increase attention to other sources of information did not facilitate the learning process.

Social cognition and the brain: a meta-analysis

This meta-analysis explores the location and function of brain areas involved in social cognition, or the capacity to understand people's behavioral intentions, social beliefs, and personality traits. On the basis of over 200 fMRI studies, it tests alternative theoretical proposals that attempt to explain how several brain areas process information relevant for social cognition. The results suggest that inferring temporary states such as goals, intentions, and desires of other people-even when they are false and unjust from our own perspective--strongly engages the temporo-parietal junction (TPJ). Inferring more enduring dispositions of others and the self, or interpersonal norms and scripts, engages the medial prefrontal cortex (mPFC), although temporal states can also activate the mPFC. Other candidate tasks reflecting general-purpose brain processes that may potentially subserve social cognition are briefly reviewed, such as sequence learning, causality detection, emotion processing, and executive functioning (action monitoring, attention, dual task monitoring, episodic memory retrieval), but none of them overlaps uniquely with the regions activated during social cognition. Hence, it appears that social cognition particularly engages the TPJ and mPFC regions. The available evidence is consistent with the role of a TPJ-related mirror system for inferring temporary goals and intentions at a relatively perceptual level of representation, and the mPFC as a module that integrates social information across time and allows reflection and representation of traits and norms, and presumably also of intentionality, at a more abstract cognitive level.

End or Means—The “What” and “How” of Observed Intentional Actions

Action understanding and learning are suggested to be mediated, at least in part, by the human mirror neuron system (hMNS). Static images as well as videos of actions with the outcome occluded have been shown to activate the hMNS. However, whether the hMNS preferentially responds to end or means of an action remains to be investigated. We, therefore, presented subjects with videos of intentional actions that were shown from two perspectives (factor 1, perspective: first vs. third person) while subjects directed their attention to the means or the end thereof (factor 2, task: means vs. end). End- or means-related changes in BOLD signal and corticospinal excitability (CSE) were assessed using fMRI and TMS, respectively. Judging the means of an action compared with its end differentially activated bilateral ventral premotor (vPMC) and inferior parietal cortex (IPL), that is, the core regions of the hMNS. The reverse contrast revealed left precuneus and bilateral superior frontal, angular, and middle temporal gyrus activity. In accordance, the two tasks, although identically in stimulus properties, modulated CSE differentially. Although recent studies suggest that the hMNS may prefer the presence of a goal or context, our data show that within the same context, it responds preferentially when attention is directed to the action means. Consequently, in addition to inferring action goals, a key function of the hMNS may be to anticipate the trajectories and dynamics of observed actions, which is a prerequisite for any timely interaction.

Culture in the mind's mirror: how anthropology and neuroscience can inform a model of the neural substrate for cultural imitative learning

Cultural neuroscience, the study of how cultural experience shapes the brain, is an emerging subdiscipline in the neurosciences. Yet, a foundational question to the study of culture and the brain remains neglected by neuroscientific inquiry: "How does cultural information get into the brain in the first place?" Fortunately, the tools needed to explore the neural architecture of cultural learning - anthropological theories and cognitive neuroscience methodologies - already exist; they are merely separated by disciplinary boundaries. Here we review anthropological theories of cultural learning derived from fieldwork and modeling; since cultural learning theory suggests that sophisticated imitation abilities are at the core of human cultural learning, we focus our review on cultural imitative learning. Accordingly we proceed to discuss the neural underpinnings of imitation and other mechanisms important for cultural learning: learning biases, mental state attribution, and reinforcement learning. Using cultural neuroscience theory and cognitive neuroscience research as our guides, we then propose a preliminary model of the neural architecture of cultural learning. Finally, we discuss future studies needed to test this model and fully explore and explain the neural underpinnings of cultural imitative learning.

Sensorimotor cortex as a critical component of an 'extended' mirror neuron system: Does it solve the development, correspondence, and control problems in mirroring?

A core assumption of how humans understand and infer the intentions and beliefs of others is the existence of a functional self-other distinction. At least two neural systems have been proposed to manage such a critical distinction. One system, part of the classic motor system, is specialized for the preparation and execution of motor actions that are self realized and voluntary, while the other appears primarily involved in capturing and understanding the actions of non-self or others. The latter system, of which the mirror neuron system is part, is the canonical action 'resonance' system in the brain that has evolved to share many of the same circuits involved in motor control. Mirroring or 'shared circuit systems' are assumed to be involved in resonating, imitating, and/or simulating the actions of others. A number of researchers have proposed that shared representations of motor actions may form a foundational cornerstone for higher order social processes, such as motor learning, action understanding, imitation, perspective taking, understanding facial emotions, and empathy. However, mirroring systems that evolve from the classic motor system present at least three problems: a development, a correspondence, and a control problem. Developmentally, the question is how does a mirroring system arise? How do humans acquire the ability to simulate through mapping observed onto executed actions? Are mirror neurons innate and therefore genetically programmed? To what extent is learning necessary? In terms of the correspondence problem, the question is how does the observer agent know what the observed agent's resonance activation pattern is? How does the matching of motor activation patterns occur? Finally, in terms of the control problem, the issue is how to efficiently control a mirroring system when it is turned on automatically through observation? Or, as others have stated the problem more succinctly: "Why don't we imitate all the time?" In this review, we argue from an anatomical, physiological, modeling, and functional perspectives that a critical component of the human mirror neuron system is sensorimotor cortex. Not only are sensorimotor transformations necessary for computing the patterns of muscle activation and kinematics during action observation but they provide potential answers to the development, correspondence and control problems.

The what and how of observational learning

Neuroimaging evidence increasingly supports the hypothesis that the same neural structures subserve the execution, imagination, and observation of actions. We used repetitive transcranial magnetic stimulation (rTMS) to investigate the specific roles of cerebellum and dorsolateral prefrontal cortex (DLPFC) in observational learning of a visuomotor task. Subjects observed an actor detecting a hidden sequence in a matrix and then performed the task detecting either the previously observed sequence or a new one. rTMS applied over the cerebellum before the observational training interfered with performance of the new sequence, whereas rTMS applied over the DLPFC interfered with performance of the previously observed one. When rTMS applied over cerebellar or prefrontal site was delivered after the observational training, no influence was observed on the execution of the task. These results furnish new insights on the neural circuitry involved in the single component of observational learning and allow us to hypothesize that cerebellum and DLPFC interact in planning actions, the former by permitting the acquisition of procedural competencies and the latter by providing flexibility among already acquired solutions.

Switching language switches mind: linguistic effects on developmental neural bases of 'Theory of Mind'

Theory of mind (ToM)--our ability to predict behaviors of others in terms of their underlying intentions--has been examined through false-belief (FB) tasks. We studied 12 Japanese early bilingual children (8-12 years of age) and 16 late bilingual adults (18-40 years of age) with FB tasks in Japanese [first language (L1)] and English [second language (L2)], using fMRI. Children recruited more brain regions than adults for processing ToM tasks in both languages. Moreover, children showed an overlap in brain activity between the L1 and L2 ToM conditions in the medial prefrontal cortex (mPFC). Adults did not show such a convergent activity in the mPFC region, but instead, showed brain activity that varied depending on the language used in the ToM task. The developmental shift from more to less ToM specific brain activity may reflect increasing automatization of ToM processing as people age. These results also suggest that bilinguals recruit different resources to understand ToM depending on the language used in the task, and this difference is greater later in life.

Autism and the amygdala: An endocrine hypothesis

Children become oriented to the world, in part, by coming to understand something of the experiences of others. The facial expressions that people make are an avenue for understanding something about them, as are the diverse forms of bodily responses emitted and interpreted by individuals. People with autism often find bodily communications to be aversive, thereby limiting what they can learn from others during social interactions. The amygdala is an important area of the brain, amongst others, for integrating the internal milieu with the social ambiance. Individuals with autism consistently demonstrate dysregulation of amygdala function. Diverse regions of the amygdala, which contain neuropeptides, figure in the appraisal systems that underlie behavioral approach and avoidance responses. One neuropeptide linked to social recognition and approach behaviors is oxytocin (which is known to be decreased in autistic individuals) and another neuropeptide corticotropin releasing hormone is tied to avoidance behaviors. A neuroendocrine hypothesis is suggested to account for some of the features associated with autism.

"Do what I do" and "do how I do": different components of imitative learning are mediated by different neural structures

The involvement of different neural structures in imitative learning was studied in two paradigms. In an experimental paradigm, rats observed actor rats learning spatial procedures in a water maze. After the observational training, the observers underwent a cerebellar lesion, preventing further procedural acquisitions, and then were tested in the water maze previously observed. The cerebellar networks appear to be indispensable for acquiring by imitation the spatial procedures. The procedural sequence was then dissected into the single behavioral units, demonstrating that such units do exist and can be independently acquired. By using repetitive transcranial magnetic stimulation (rTMS), the role of the cerebellum and prefrontal cortex in imitative learning was investigated in humans. Subjects observed an actor detecting a hidden sequence in a matrix and then performed the task detecting either the previously observed sequence or a new one. Cerebellar rTMS applied before the observational training interfered with performance of the new sequence, whereas prefrontal rTMS interfered also with performance of the previously observed one. rTMS delivered after the observational training did not influence task execution. These findings indicate that the cerebellum and prefrontal cortex interact in planning actions, the former by permitting the acquisition by imitation of procedural competencies and the latter by providing flexibility among already acquired solutions.

Cultural and linguistic effects on neural bases of 'Theory of Mind' in American and Japanese children

Theory of Mind (ToM) has been defined as our ability to predict behaviors of others in terms of their underlying intentions. While the developmental trajectory of ToM had been thought to be invariant across cultures, several ToM studies conducted outside the Anglo-American cultural or linguistic milieus have obtained mixed results. To examine effects of culture/language on the development of neural bases of ToM, we studied 12 American monolingual children and 12 Japanese bilingual children with second-order false-belief story and cartoon tasks, using functional magnetic resonance imaging (fMRI). While a few brain regions such as ventro-medial prefrontal cortex (vmPFC) and precuneus were recruited by both cultural/linguistic groups, several brain areas including inferior frontal gyrus (IFG) and temporo-parietal junction (TPJ) were employed in a culture/language-dependent manner during the ToM tasks. These results suggest that the neural correlates of ToM may begin to vary depending upon cultural/linguistic background from early in life.

'Like me': a foundation for social cognition

Infants represent the acts of others and their own acts in commensurate terms. They can recognize cross-modal equivalences between acts they see others perform and their own felt bodily movements. This recognition of self-other equivalences in action gives rise to interpreting others as having similar psychological states such as perceptions and emotions. The 'like me' nature of others is the starting point for social cognition, not its culmination.

Neural mechanisms underlying immediate and final action goals in object use reflected by slow wave brain potentials

Event-related brain potentials were used to study the neural mechanisms underlying goal-directed object use distinguishing between processes supporting immediate and final action goals during action planning and execution. Subjects performed a grasping and transportation task in which actions were cued either with the immediate action goal (the part of the object to grasp) or with the final action goal of the movement (the end position for transportation). Slow wave potentials dissociated between processes supporting immediate and final goals: reaching for the object was accompanied by the development of a parietal-occipital slow wave that peaked in congruency with the grasping event, whereas transport of the object towards the final goal location was found accompanied by slow wave components developing over left frontal regions with a peak towards the movement end. Source localization of cueing differences indicated activation centered around the parieto-occipital sulcus during reaching of the immediate action goal, followed by enhanced activation in the anterior prefrontal cortex during transport to the final action goal. These results suggest the existence of separate neural controllers for immediate and final action goals during the execution of goal-directed actions with objects.

What is modelled during observational learning?

In this article, we examine the question of what information is processed during observational learning by evaluating a variety of methods, theories, and empirical data. Initially, we review work involving neuroimaging techniques and infant imitation. We then evaluate data from behavioural experiments involving adults, wherein a variety of attempts have been made to isolate the critical or minimal information constraining the acquisition of coordination. This body of research has included comparisons between video and point-light displays, manipulations to the amount and type of information presented in the display, the collection of point-of-gaze data, and manipulations to the task context in terms of outcome goals. We conclude that observational learning is governed by specific features of the model's action (i.e. motions of the end effector) and the task (i.e. outcome constraints) and, in contrast with traditional theoretical modelling, more global aspects of a model (i.e. the relative motions within and between joints) do not appear to be the primary method for constraining action execution.

Children's and adults' neural bases of verbal and nonverbal 'theory of mind'

Theory of mind (ToM) - our ability to predict behaviors of others in terms of their underlying intentions - has been examined through verbal and nonverbal false-belief (FB) tasks. Previous brain imaging studies of ToM in adults have implicated medial prefrontal cortex (mPFC) and temporo-parietal junction (TPJ) for adults' ToM ability. To examine age and modality related differences and similarities in neural correlates of ToM, we tested 16 adults (18-40 years old) and 12 children (8-12 years old) with verbal (story) and nonverbal (cartoon) FB tasks, using functional magnetic resonance imaging (fMRI). Both age groups showed significant activity in the TPJ bilaterally and right inferior parietal lobule (IPL) in a modality-independent manner, indicating that these areas are important for ToM during both adulthood and childhood, regardless of modality. We also found significant age-related differences in the ToM condition-specific activity for the story and cartoon tasks in the left inferior frontal gyrus (IFG) and left TPJ. These results suggest that depending on the modality adults may utilize different brain regions from children in understanding ToM.

The 'like me' framework for recognizing and becoming an intentional agent

Infant imitation demonstrates that the perception and production of human action are closely linked by a 'supramodal' representation of action. This action representation unites observation and execution into a common framework, and it has far-reaching implications for the development of social cognition. It allows infants to see the behaviors of others as commensurate with their own-as 'like me.' Based on the 'like me' perception of others, social encounters are interpretable and informative. Infants can use themselves as a framework for understanding others and can learn about the possibilities and consequences of their own potential acts by observing the behavior of others. Through social interaction with other intentional agents who are viewed as 'like me,' infants develop a richer social cognition. This paper explores the early manifestations and cascading developmental effects of the 'like me' conception.

The neural processing of moral sensitivity to issues of justice and care

The empirical and theoretical consideration of ethical decision making has focused on the process of moral judgment; however, a precondition to judgment is moral sensitivity, the ability to detect and evaluate moral issues [Rest, J. R. (1984). The major components of morality. In W. Kurtines & J. Gewirtz (Eds.), Morality, moral behaviour, and moral development (pp. 24-38). New York, NY: Wiley]. Using functional magnetic resonance imaging (fMRI) and contextually standardized, real life moral issues, we demonstrate that sensitivity to moral issues is associated with activation of the polar medial prefrontal cortex, dorsal posterior cingulate cortex, and posterior superior temporal sulcus (STS). These activations suggest that moral sensitivity is related to access to knowledge unique to one's self, supported by autobiographical memory retrieval and social perspective taking. We also assessed whether sensitivity to rule-based or "justice" moral issues versus social situational or "care" moral issues is associated with dissociable neural processing events. Sensitivity to justice issues was associated with greater activation of the left intraparietal sulcus, whereas sensitivity to care issues was associated with greater activation of the ventral posterior cingulate cortex, ventromedial and dorsolateral prefrontal cortex, and thalamus. These results suggest a role for access to self histories and identities and social perspectives in sensitivity to moral issues, provide neural representations of the subcomponent process of moral sensitivity originally proposed by Rest, and support differing neural information processing for the interpretive recognition of justice and care moral issues.

'Like me': a foundation for social cognition

Infants represent the acts of others and their own acts in commensurate terms. They can recognize cross-modal equivalences between acts they see others perform and their own felt bodily movements. This recognition of self-other equivalences in action gives rise to interpreting others as having similar psychological states such as perceptions and emotions. The 'like me' nature of others is the starting point for social cognition, not its culmination.

Weaving the fabric of social interaction: articulating developmental psychology and cognitive neuroscience in the domain of motor cognition

In this article, we bring together recent findings from developmental science and cognitive neuroscience to argue that perception-action coupling constitutes the fundamental mechanism of motor cognition. A variety of empirical evidence suggests that observed and executed actions are coded in a common cognitive and neural framework, enabling individuals to construct shared representations of self and other actions. We review work to suggest that such shared representations support action anticipation, organization, and imitation. These processes, along with additional computational mechanisms for determining a sense of agency and behavioral regulation, form the fabric of socialinteraction. In addition, humans possess the capacity to move beyond these basic aspects of action analysis to interpret behavior at a deeper level, an ability that may be outside the scope of the mirror system. Understanding the nature of shared representations from the vantage point of developmental and cognitive science and neuroscience has the potential to inform a range of motor and social processes. This perspective also elucidates intriguing new directions and research questions and generates specific hypotheses regarding the impact of early disorders (e.g., developmental movement disorders) on subsequent action processing.

The mirror neuron system and the consequences of its dysfunction

The discovery of premotor and parietal cells known as mirror neurons in the macaque brain that fire not only when the animal is in action, but also when it observes others carrying out the same actions provides a plausible neurophysiological mechanism for a variety of important social behaviours, from imitation to empathy. Recent data also show that dysfunction of the mirror neuron system in humans might be a core deficit in autism, a socially isolating condition. Here, we review the neurophysiology of the mirror neuron system and its role in social cognition and discuss the clinical implications of mirror neuron dysfunction.

Imitative response tendencies following observation of intransitive actions

Clear and unequivocal evidence shows that observation of object affordances or transitive actions facilitates the activation of a compatible response. By contrast, the evidence showing response facilitation following observation of intransitive actions is less conclusive because automatic imitation and spatial compatibility have been confounded. Three experiments tested whether observation of a finger movement (i.e., an intransitive action) in a choice reaction-time task facilitates the corresponding finger movement response because of imitation, a common spatial code, or some combination of both factors. The priming effects of a spatial and an imitative stimulus were tested in combination (Experiment 1), in opposition (Experiment 2), and independently (Experiment 3). Contrary to previous findings, the evidence revealed significant contributions from both automatic imitation and spatial compatibility, but the priming effects from an automatic tendency to imitate declined significantly across a block of trials whereas the effects of spatial compatibility remained constant or increased slightly. These differential effects suggest that priming associated with automatic imitation is mediated by a different regime than priming associated with spatial compatibility.