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Mirror neurons: fundamental discoveries, theoretical perspectives and clinical implications

Mirror neurons discharge both when we execute and when we observe a specific action. It is astonishing to witness how much the social neurosciences and psychology have been influenced by the discovery of mirror neurons. The mirror mechanism is present in many cortical areas and brain centres of birds, monkeys and humans; with functions ranging from song production, to the organisation of goal-directed motor acts, to emotional processes. Despite a growing number of empirical investigations on mirror neurons, several questions remain to be clarified about their emergence and functions. This themed issue of Philosophical Transactions of the Royal Society B presents state of the art research in contemporary mirror mechanism studies. Based on recent new findings, it sheds light on the basic mechanisms, anatomical substrates, human-monkey differences, emergence during ontogeny, principal functions and psychopathologies related to impairment in these systems. The contributions in this issue dissect these topics, address controversial issues and provide a framework to stimulate new research directions.

Research includes: How mirror neurons might help children understand other people’s actions to learn skills, tool use and cultural practices; how understanding the mirror neuron system could help in the development of new approaches to autism; and how mechanisms which control imitation could help us resist our human urge to copy the behaviour of others.

Autism and the mirror neuron system: insights from learning and teaching

by Vivanti, Giacomo; Rogers, Sally

Children with autism spectrum disorders (ASD) typically have difficulties with social learning involving the kinds of tasks that typically involve the mirror neuron system. New insights on the role of the mirror neuron system in autism can be gained by studying several aspects of social learning, including relations to the reward value of social experiences, strategic/ selective use of others’ knowledge, and the study of response to intervention strategies focused on social learning. Recent work on the responses of children with autism to naturalistic developmental/behavioural interventions like the Early Start Denver Model, which emphasizes social imitation, dyadic engagement, language and affect sharing, may help shed light on the nature of the neuropsychological mechanisms underlying social learning and positive treatment outcomes in autism. This knowledge in turn may assist in developing more successful pedagogic approaches to ASD.

What are you doing? How active and observational experience shape infants’ action understanding

by Hunnius, Sabine; Bekkering, Harold

From early in life, infants watch other people’s actions. How do young infants come to make sense of actions they observe? Here, we review empirical findings which demonstrate the crucial role of infants’ own action experience for their understanding of others’ actions. In addition, infants have been shown to come to an understanding of others’ actions through the repeated observation of actions and the effects associated with them. We argue that based on these two forms of experience – active action experience and observational experience – infants gradually develop more complex action understanding capabilities.

Neural systems for preparatory control of imitation

by Cross, Katy; Iacoboni, Marco

Imitation is a pervasive human behaviour important for learning and transmission of culture. In some situations, however, it is important to be able to control imitative behaviour, as for instance when social cues may facilitate relapse in alcohol or substance abuse. Here we show important brain mechanisms for imitation control that can help designing interventions for improving the control of imitative behaviour.

Neural mirroring mechanisms and imitation in human infants

by Marshall, Peter; Meltzoff, Andrew

Human infants imitate a wide range of behaviours they observe being carried out by others. The ability to successfully imitate indicates that infants can use the acts perceived by others to generate their own matching acts. Through the social context of imitation, children learn skills, tool-use techniques, and cultural practices. There is increasing interest in the neuroscience of imitation in infancy. This paper documents recent evidence involving the use of EEG methods to study infant imitation and early social understanding.

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

by Simpson, Elizabeth; Murray, Lynne; Annika, Paukner; Ferrari, Pier

There is strong evidence that neonates imitate previously unseen behaviours, such as facial expressions, demonstrating neonates’ ability and motivation to engage with others. Research on neonatal imitation can provide a wealth of information about the early mirror neuron system, a system that allows us to link the perception of others’ actions to our own actions. For instance, recent work reveals that individual differences in neonatal imitation positively correlate with later social, cognitive, and motor development. We propose that such variation in neonatal imitation could reflect important individual differences, which may allow us to detect early social deficits.

Hebbian learning and predictive mirror neurons for actions, sensations and emotions

by Keysers, Christian; Gazzola, Valeria

We often effortlessly understand the people around us. How does our brain do that? Here we argue that Hebbian learning suffices to explain how we get to have neurons in the brain that respond when we do an action, and when we hear or see others do similar actions. We show that the mirror neurons that arise from such learning would predict what others do. We further show that the kind of mind-reading performed by these mirror neurons is an egocentrically biased projection. Finally we argue that we have similar systems for sharing the actions and sensations of others.

Listening to speech recruits specific tongue motor synergies as revealed by transcranial magnetic stimulation and tissue-Doppler ultrasound imaging

by D’Ausilio, Alessandro; Maffongelli, Laura; Bartoli, Eleonora; Campanella, Martina; Ferrari, Elisabetta; Berry, Jeffrey; Fadiga, Luciano

When we listen to speech we don’t just use our listening abilities but rather we replicate what we hear with our motor system. Here we demonstrate that such a process is extremely accurate down to the implementation of the complete vocal tract simulation of what the speaker is doing.

Mirroring and the development of action understanding

by Woodward, Amanda; Gerson, Sarah

This theoretical review paper brings together insights from the scientific study of infant social cognition, motor development and neuroscience to evaluate whether, and how, mirror neurons may be implicated in understanding others’ actions.

Auditory-vocal mirroring in songbirds

by Mooney, Richard

This review considers evidence of auditory vocal mirror neurons in songbirds, which resemble humans in their capacity for vocal learning. Songbird mirror neurons are well suited to facilitate vocal learning and communication, and study of these cells promises to shed light on the computational and developmental mechanisms which give rise to mirror neurons.

Frequency and topography in monkey electroencephalogram during action observation: possible neural correlates of the mirror-neuron system

by Coudé, Gino; Vanderwert, Ross; Thorpe, Samuel; Festante, Fabrizia; Bimbi, Marco; Fox, Nathan; Ferrari, Pier

The observation of actions executed by others results in desynchronization of alpha and beta rhythms. On the other hand, mirror neurons, which are thought to be responsible for this effect, have only been studied in macaque monkeys. Here we record electroencephalogram (EEG) from the scalp of two monkeys during action observation. We found that action observation produced desynchronization in the 19 – 25 Hz band that was strongest over anterior and central electrodes. These results are in line with human data showing that specific frequency bands within the power spectrum of the ongoing EEG may be modulated by observation of actions and therefore might be a specific marker of mirror neurons activity.

Human primary motor cortex is both activated and stabilized during observation of other person’s phasic motor actions [OPEN ACCESS]

by Hari, Riitta; Bourguignon, Mathieu; Piitulainen, Harri; Smeds, Eero; De Tiège, Xavier; Jousmäki, Veikko

We show, by means of magnetoencephalograpic (MEG) recordings in healthy humans, that when the subjects view motor actions of other persons, their own motor cortex is both activated (as has been shown earlier) and inhibited (novel finding). These apparently opposite effects occur at different frequency bands and increase our understanding of “mirroring” mechanisms. When we see others’ actions, our own motor system is activated but, because of motor-cortex inhibition, so that we do not automatically imitate their actions which would often be socially inappropriate.

The mirror mechanism: recent findings and perspectives

by Rizzolatti, Giacomo; Fogassi, Leonardo

Mirror neurons are a specific type of visuomotor neurons that discharge both when a monkey executes a motor act and when it observes a similar motor act performed by another individual. We here describe visual features of mirror responses that indicate that, besides encoding the goal of motor acts, mirror neurons are modulated by location in space of the observed motor acts, by the perspective from which the others’ motor acts are seen, and by the value associated to the object on which others’ motor acts are performed. These findings are of great interest for comprehension on how others’ actions and intentions are understood.

Corticospinal mirror neurons [OPEN ACCESS]

by Kraskov, A, Philipp, R, Waldert, S, Vigneswaran, G, Quallo, MM and Lemon, RN

Since their discovery, mirror neurons have been in equal measure fascinating and controversial. A number of functional roles have been proposed, but actually we do not know whether the connections made by mirror neurons in the brain are appropriate for these roles. In this report we focus on the properties of a particular subset of cortical mirror neurons where we have been able to define their output target. We identified these mirror neurons as pyramidal tract neurons (PTNs). PTNs send their axons through the pyramidal tract down into the spinal cord. The neurons were recorded in two nodes of the cortical motor network: the ventral premotor cortex (area F5) and primary motor cortex (M1). A considerable proportion of tested PTNs showed clear mirror-like properties (49% for F5, 58% for M1) i.e. their discharge was modulated both by the monkey’s own action (in this case grasp), and by the monkey watching a human experimenter perform a similar grasp. Some PTNs exhibited ‘classical’ mirror neuron properties, increasing activity for both execution and observation, while others considerably decreased their discharge during observation (‘suppression mirror-neurons’). PTNs contribute to one of the major pathways from cortex to spinal cord that is involved in the generation of voluntary movements. Yet despite these PTNs modulating their discharge as they watched the experimenter’s grasping actions, the monkeys themselves showed no sign of movement and recordings from their hand and arm muscles confirmed this. Indeed we suggest that the mirror neuron system is involved in the withholding of unwanted movement during action observation, and is able to switch rapidly between making your own movements and observing those of others.

Tinbergen on mirror neurons

by Heyes, Cecilia

Fifty years ago, Niko Tinbergen defined the scope of behavioural biology with his four problems: causation, ontogeny, survival value and evolution. About 20 years ago, there was another highly significant development in behavioural biology – the discovery of mirror neurons. Here I use Tinbergen’s four problems to highlight the differences between two accounts of mirror neurons; to suggest that the associative account provides the best explanation for current data on the causation and ontogeny of mirror neurons; and to argue that functional analysis, of the kind Tinbergen identified with studies of ‘survival value’, should be a high priority for future research.

Bodily selves in relation: embodied simulation as second-person perspective on intersubjectivity

by Gallese, Vittorio

This paper proposes a new take on intersubjectivity, based on a minimal account of the self, the bodily self, viewed first and foremost in terms of its motor potentialities. Embodied simulation theory is proposed as a functional mechanism at the basis of basic aspects of social cognition and fully compatible with a second-person approach to intersubjectivity.

Dyadic brain modelling, mirror systems and the ontogenetic ritualization of ape gesture

by Arbib, Michael; Ganesh, Varsha; Gasser, Brad

Mirror neurons are by now well known but almost no research assesses the role of mirror neurons in self-action or follows through on the role of recognizing others’ actions in determining one’s own course of action. We argue that computer modelling of these aspects can develop novel hypotheses ripe for experimental investigation in monkeys, apes and humans. We thus introduce the notion of Dyadic Brain Modelling to provide both a framework for modelling each brain of interacting agents and a general framework for simulating and visualizing the interactions generated when the overall brain (and the two bodies) are each coded up in computational detail. We also demonstrate the importance of trajectory level generation and recognition of actions, and the need of each agent to keep track of both proximal and distal goals of self and other. To demonstrate this methodology, we show that ontogenetic ritualization, a means whereby (some) ape gestures could emerge as praxic actions give way to intransitive gestures in achieving certain goals, emerges in a computational model of dyadic interaction.

Action observation treatment: a novel tool in neurorehabilitation

by Buccino, Giovanni

Action observation treatment (AOT) is a novel approach in neurorehabilitation well grounded in neurophysiology, thus representing a valid model of translational medicine in the field of neurorehabilitation. The results concerning its effectiveness have been collected in randomized controlled studies: in this respect it is an example of evidence based clinical practice. So far it has been applied in the motor recovery of patients with neurological and non neurological diseases. Larger studies should aim at defining the groups of patients who may most benefit from it, how biological parameters change following AOT and, finally, how to combine this approach with others well assessed tools in neurorehabilitation.

Neurofeedback training produces normalization in behavioural and electrophysiological measures of high-functioning autism

by Pineda, Jaime; Carrasco, Karen; Datko, Mike; Pillen, Steven; Schalles, Matt

Autism is a neurodevelopmental condition characterized by impairments in behaviour, social, and communication skills. Recent studies have shown that the autistic brain contains aberrant connections that can impact synchronization and effective neural communication producing abnormal social cognition. We tested whether neurofeedback training (NFT) reduces symptoms in children with high-functioning autism by targeting training to the mirror neuron system. The results show behavioural and electrophysiological improvements in autism subjects but not in typically developing children. This suggests that NFT can produce normalization in dysfunctional mirroring networks, but the benefits do not extend to brains with no abnormal connections.

Edited and compiled by: Pier Francesco Ferrari and Giacomo Rizzolatti

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Please note that both the media summaries and the journal issue itself represent the views of the authors and not the position of the Royal Society.

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