more than an imitation game top down modulation of the human mirror system

Accepted Manuscript Title: More than an Imitation Game: Top-down Modulation of the Human Mirror System Authors: Megan E.J Campbell, Ross Cunnington PII: DOI: Reference: S0149-7634(16)30597-8 http://dx.doi.org/doi:10.1016/j.neubiorev.2017.01.035 NBR 2746 To appear in: Received date: Revised date: Accepted date: 30-9-2016 16-1-2017 25-1-2017 Please cite this article as: Campbell, Megan E.J., Cunnington, Ross, More than an Imitation Game: Top-down Modulation of the Human Mirror System.Neuroscience and Biobehavioral Reviews http://dx.doi.org/10.1016/j.neubiorev.2017.01.035 This is a PDF file of an unedited manuscript that has been accepted for publication As a service to our customers we are providing this early version of the manuscript The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain MORE THAN AN IMITATION GAME: TOP-DOWN MODULATION OF THE HUMAN MIRROR SYSTEM Literature Review Megan E J Campbell1 and Ross Cunnington1,2 The Queensland Brain Institute, School of Psychology, The University of Queensland, St Lucia, 4072, Australia HIGHLIGHTS     Mirroring properties are acquired and malleable Context, task-relevance and prior sensorimotor experience modulate mirror system activity Mirror system regions are involved in non-imitative action responses Cognitive control networks can modulate learned mirror representations for counterimitation ABSTRACT All interpersonal interactions are underpinned by action: perceiving and understanding the actions of others, and responding by planning and performing self-made actions Perception of action, both self-made and observed, informs ongoing motor responses by iterative feedback within a perception-action loop This fundamental phenomenon occurs within single-cells of the macaque brain which demonstrate sensory and motor response properties These ‘mirror’ neurons have led to a swathe of research leading to the broadly accepted idea of a human mirror system The current review examines the putative human mirror system literature to highlight several inconsistencies in comparison to the seminal macaque data, and ongoing controversies within human focused research (including mirror neuron origin and function) In particular, we will address the often-neglected other side to the ‘mirror’: complementary and opposing actions We propose that engagement of the mirror system in meeting changing task-demands is dynamically modulated via frontal control networks Keywords: mirror neuron system; cognitive control; sensorimotor associations; perceptionaction; imitation; counter-imitation INTRODUCTION Perception and action are inextricably linked processes, and together form the basis of every aspect of our experience of and interaction with the world Of particular importance are the interactions humans have with each other These require complex, concurrent processes for perceiving the actions of the self and other Such perceptual representations inform the preparation of corresponding motor responses, through to the execution of the action and the perception of the outcome of this action (known as the perception-action-loop) A phenomenon variously termed motor resonance (e.g Cross and Iacoboni, 2014a), mirroring (Rizzolatti and Fogassi, 2014) and vicarious activation (Keysers and Gazzola, 2009), has been identified as a critical part of this perception-action-loop Of course this began with the report of ‘mirror neurons’ in the premotor cortex of the rhesus macaque, discovered some 20 years ago by Rizzolatti’s group (di Pellegrino et al., 1992; Gallese et al., 1996) Mirroring refers to the apparently similar neural processing of observed actions as for self-made actions, particularly within regions of the brain previously thought of as selectively coding motor control, i.e self-made actions Critically we avoid a definition based on a strict congruence between observed and executed actions Here we review the human ‘mirror system’ literature to highlight a number of inconsistencies with the original macaque data, and to discuss ongoing controversies within the field By contrasting various theories of mirror system origin and function, we point to a convergence of views and provide a useful framework from which to pose further questions In particular, we will address the often-neglected other side to the ‘mirror’, i.e complementary and opposing action responses, and how an action “mirroring” system might allow alternative task-demands to be met Some level of ‘mirroring’ may always occur (Kilner et al., 2003), but we argue these representations are propagated depending on prior associations between stimulus and response actions, and the context of the task at hand Control processes, such as response-selection, conflict detection, and ongoing goal-maintenance can be engaged to gauge the task-relevance of incoming sensory information to optimise the generation of motor responses Even in situations where stimulus and response actions are not perfectly compatible, the mirrored representations of observed actions may still be usefully integrated to prepare complementary responses We argue that activation of mirror regions is dynamically adaptive and integrated with the top-down control systems of frontal networks Cognitive control collectively refers to higher-order executive functions which enable one to coordinate lower-level processing toward meeting internal goals, while remaining flexible to changing demands (Dosenbach et al., 2008; Koechlin et al., 2003) These processes and the networks underlying them have been reviewed in detail elsewhere (for theoretical review Botvinick et al., 2001; Miller and Cohen, 2003; Ridderinkhof et al., 2004) Here we focus on the influence of cognitive control on dynamic, adaptive and predictive sensorimotor associations in the action-perception and motor-response loop This view aligns with the associative sequence learning account of mirror neuron development and evolution (Heyes, 2010a), a parsimonious theory for the sensorimotor associations linking the representations of both observed and executed actions Hence, we apply a system-level framework to sensorimotor mirroring, incorporating existing cognitive and computational models of how the brain optimises behavioural responses to sensory information (Kilner et al., 2007a; Körding and Wolpert, 2004) MIRROR NEURON TO MIRROR SYSTEM How we conceive of action perception and action execution has profoundly changed by the discovery of motor neurons with sensory properties in the ventral premotor region F5 in the macaque monkey, (di Pellegrino et al., 1992; Gallese et al., 1996) The response properties of these cells vary but their distinguishing feature is that their firing is modulated both by action execution and action observation, varying depending on the degree of action specificity The coining of the term ‘mirror neuron’ describes this unique feature of being responsive to both motor and sensory action-related inputs The purported function of mirror neurons is not ubiquitously agreed upon (e.g Casile et al., 2011; Cook and Bird, 2013; Hickok, 2013) Many researchers refer to mirror neurons as encoding action-goals and subserving action understanding, without clarifying these functions or how such functionality arises Although much of the monkey physiology data seemed to demonstrate specificity of responses to goal-directed actions (i.e object-oriented as in picking up food), Ferrari and colleagues have shown non-goal directed mouth actions (‘communicative’ gestures) to elicit activity in mirror neurons in the monkey pre-ventral cortex (Ferrari et al., 2003) Hence the idea of mirror neurons only responding to goaldirected actions is left wanting (Catmur, 2012) This is not to imply that higher-order cognition about intentions and goals are not influenced by mirror-matching sensorimotor information; however, there is a tendency in the literature to over-simplify the description of ‘mirroring’ and then ascribe extraordinary consequences to this mechanism (Heyes, 2010b; Kilner and Lemon, 2013) This is further confused by hypothesised functions of mirror neurons becoming entangled with explaining the origin of mirror neurons The genetic account of mirror neurons assumes their fundamental role is action understanding, for which the development of mirror neurons is genetically predisposed due to natural selection pressure favouring this function (Lepage and Théoret, 2007; Rizzolatti and Craighero, 2004) Therefore, the hypothesised function of mirror neurons is offered as an account of the origin of mirror neurons (Cook et al., 2014) This view of mirror neurons was apparently affirmed by neonatal imitation research (e.g seminal studies Meltzoff & Moore, 1977, 1989; and more recent review chapter: Meltzoff, 2002) However, this line of evidence has been strongly refuted by a recent longitudinal study (Oostenbroek, Suddendorf, Nielsen et al., 2016) Epigenetic accounts improve on the rigid genetic perspective by incorporating the influence of learning and experience, while arguing for a level of innate properties upon which experience builds (Bonini and Ferrari, 2011; Ferrari et al., 2013; Giudice et al., 2009) As such, this epigenetic perspective draws nearer to a view of mirror properties being experience-based 2.1 EXPERIENCE-BASED MIRRORING The Associative Sequence Learning account of mirror neurons offers a parsimonious explanation for how neurons acquire mirroring properties: sensorimotor associations form based on the experience of contingent and repeated activation of a sensory and a motor representation of a particular action (Catmur, 2012; Catmur et al., 2009; Cook et al., 2014; Heyes, 2013; 2010a; Hickok and Hauser, 2010, Heyes, 2016) Being experience-based, such connections are adaptable which allows for a wide variety of sensory inputs to mirror neurons These then code for particular motoric responses experienced in contingent relationships with a certain range of effective sensory inputs over the course of an individual’s learning history (Catmur, 2012) The domain-general process of associative learning allows for mirror neurons to make contributions to action understanding and social cognition but does not assume this (Cook et al., 2014) From this perspective mirroring may be active for imitation without being for imitation (Brass & Heyes, 2005; Hickok, 2013) Thus action understanding can take advantage of automatic imitation without precluding experience-based changes in sensorimotor associations and context-dependent inhibition of imitative tendencies A complementary account of mirroring is the Hebbian learning model proposed by Keysers and colleagues (Keysers and Gazzola, 2014; Keysers and Perrett, 2004) Based on anatomical connectivity of the macaque brain, Keysers summarises the mirror circuitry as a series of reciprocal connections between area PF of the inferior parietal lobule and both premotor area F5 and the superior temporal sulcus (STS, Keysers and Perrett, 2004) All three of these areas respond to the sight of another agent’s action, but only areas PF and F5 also respond to the monkey’s self-generated actions To explain the mirror properties of F5 and PF, Keysers and Perrett apply the Hebbian learning rule of consistent repeated cellfiring increasing the efficiency of synaptic connections between pre and post-synaptic cells, and thus leading to spike-timing dependent synaptic plasticity Importantly in their model of STS-PF-F5 circuit, the STS functions to cancel out the agent’s own movements based on temporal correlations between visual, auditory and motor representations occurring during the action observation and self-made action execution It is hypothesised that a similar feedback loop exists in the human neocortex, between homologue regions (Keysers and Gazzola, 2014).These two perspectives, Hebbian and associative, are not mutually exclusive and rather offer insight to different levels of abstraction The Associative Sequence Learning account (Catmur et al., 2009; Heyes, 2010a), a cognitive model, is focused at the functional level, and remains agnostic about the precise neural mechanisms underlying the acquisition of new associations As such it is compatible with the Hebbian learning predictions for the neural level, with spike-timing dependent plasticity reflecting contingent sensory and motor inputs Further insight into the functioning of mirror neurons is offered by the computational perspective of predicative coding via Bayesian inference Importantly, this view also holds that experience is a significant factor for mirroring Kilner (2007b) focuses on a systems-level model of the predictive and generative feedback between sensory and motor representations Predictive coding is based on minimising error via reciprocal interactions between a hierarchy of cortical areas in a Bayes optimal fashion Each level generates predictions based on the representations in the level below and concurrently feeds backwards to the lower level for comparison with the latest sensory input to produce prediction errors This error is then reiterated to the higher level to update predictions, providing contextual guidance towards the most likely cause of sensory inputs (Kilner et al., 2007b) Within this framework, mirror neuron firing rates are open to top-down modulation Firing during action observation is not merely driven by visual input, rather it constitutes a part of a generative model actively predicting sensory input By extension, sensorimotor connections and predictive coding allow for optimizing motor planning and control in the face of sensory uncertainty (Körding and Wolpert, 2004; Wolpert et al., 2011; Wolpert and Landy, 2012) This predictive coding framework is also compatible with Associative Sequence and Hebbian learning perspectives Together these provide an explanation of how repeated experience of sensorimotor associations build predictive expectancies, which are reflected in the one-to-many (motor to sensory) response mapping properties of mirror neurons Despite the convergence of theories that view mirroring as a result of experience, human ‘mirror system’ studies often tend towards both over-simplification in the undue emphasis of congruent mirror matching and an aggrandisement of what the putative human mirror system is able to achieve Cook and Bird (2013) highlight a glaring inconsistency between the seminal mirror neuron studies based on direct unit-recordings (di Pellegrino et al., 1992; Gallese et al., 1996) and the commonly misconstrued simplification adopted by ‘human mirror neuron system’ studies The typical definition of the putative human mirror system places emphasis on strict sensorimotor congruency of observed and executed actions Although this fits intuitively with the term ‘mirror’, it does not reflect the complexity described by those responsible for first measuring this phenomenon: “a particular set of F5 neurons, which discharged both during monkey's active movements and when the monkey observed meaningful hand movements made by the experimenter” (Gallese et al., 1996, p 594) Indeed Gallese classified 60.9% (56 of 92 cells recorded) of mirror neurons as merely ‘broadly congruent’; the majority of these displaying activation to the observation of two or more actions (diPellegrino:1992tg ; see Casile, 2013 for a thorough review of macaque mirror neuron physiology; Gallese et al., 1996) More recent work in monkeys has described the existence of pyramidal tract neurons which discharge for the execution of an action, but are inhibited during passive observation (Kraskov et al., 2009; 2014) This was interpreted as systematically suppressing self-action representations during observation and actively preventing mirroring In the excitement to validate the existence of a human mirror neuron system much of the nuanced variability in the response properties of mirror neurons has been glossed over 2.2 A MIRROR SYSTEM IN THE HUMAN BRAIN The existence of mirror neurons in humans is broadly accepted and yet only a single report has provided direct measurement by single-cell recordings of mirror neurons in humans (Mukamel et al., 2010) All other data is based on non-invasive techniques such as functional magnetic resonance imaging (fMRI) and transcranial magnetic stimulation (TMS) In terms of fMRI-based research, the most elegant experiments have applied fMRI adaptation paradigms to the question of ‘mirror’ activity fMRI adaptation refers to the effect of repeated presentations of a sensory stimulus causing decreased firing rates in neurons which encode that stimulus feature, and by extension leads to dampening in the bloodoxygen-level dependent (BOLD) signal, relative to that elicited by a novel stimulus (Krekelberg et al., 2006, yet; for caution see, Larsson and Smith, 2012) The application of this technique to the question of the human ‘mirror system’ aims to determine the presence of neural populations selective for particular actions, regardless of whether the action was observed or executed (e.g Chong et al., 2008) However the studies published using this technique (Chong et al., 2008; Dinstein et al., 2007; Kilner et al., 2009; Lingnau et al., 2009; Press et al., 2012) have produced mixed results, with only three reporting results consistent with the presence of mirror neurons Two highlighted the inferior frontal gyrus (Kilner et al., 2009), and one the inferior parietal lobe (Chong et al., 2008), as areas homologous to the regions of the macaque fronto-parietal ‘mirror neuron system’ (areas F5 and PFG, Rizzolatti and Craighero, 2004) Another important note on these adaptation studies is that the results were not bi-directional Observation followed by execution elicited repetition suppression, but not execution followed by observation This suggests that mirroring is only involved in priming self-made actions in response to observed actions and not vice-versa, and supports the notion of sensorimotor associations (Catmur et al., 2007) rather than direct-matching models which suggests mirroring occurs regardless of modality order Thus, mirror responses reflect the facilitation of the motor system due to learned associations between sensory representations of actions and the motor programs which generate them (Catmur, 2012; Catmur et al., 2007; Hickok, 2009) Another general limitation of many of the human imaging studies reporting mirror neuron activity is the failure to include action-execution conditions corresponding to actionobservation Indeed, a meta-analysis by Molenberghs and colleagues (2012) revealed that 70% of studies reporting visuo-motor mirror effects were based on only action observation manipulations This meta-analysis did yield converging evidence of sensorimotor mirroring in cortical areas including the inferior frontal gyrus, ventral premotor cortex and inferior and superior parietal lobules (Molenberghs et al., 2012), which confirms the positive results of the handful of fMRI adaptation studies (Chong et al., 2008; Kilner et al., 2009; Press et al., 2012) Moreover these meet predictions of human homologues based on monkey single-cell physiology (Gallese et al., 1996; Kilner and Lemon, 2013) Molenberghs and colleagues (2012) describe these areas as “a core network of brain areas … which in humans is reliably activated during tasks examining the classic mirror mechanism, typically involving the visual observation and execution of actions” (p.348) Moreover, additional regions were shown to be activated relative to modality (e.g post-central gyrus for somatosensory simulation and experience), which fits in with the view heralded by Keysers and Gazzola’s group that vicarious brain activity, made possible by mirror neurons, encompasses more than actions; extending to the sensations and emotional states of others (Keysers and Gazzola, 2009) Furthermore, this perspective is compatible with the associative sequence learning account of mirror neuron development (Catmur et al., 2009; Heyes, 2013; 2010a), with principle of contingent inputs becoming associated over repeated experience being domain-general this theory permits for multi-modal ‘mirroring’ (Keysers and Gazzola, 2014) Returning to our focus on mirroring for action: the association between observed and executed actions built though common experience, leads to the sensory input of observing another’s action feeding forward as motor representations then priming a matching motor plan (Heyes, 2010a) There is firm evidence for this model of action mirroring based on multiple studies employing single-pulse transcranial magnetic stimulation (TMS) This technique can be used in conjunction with electromyography (EMG) to measure the corticospinal excitability of muscle specific representations of actions (varying size of motor-evoked potentials, MEP), and it has been shown that the passive observation of an action selectively enhances the excitability of the representations of muscles involved in executing the observed action (for example, Baldissera et al., 2001; Clark et al., 2004; Fadiga et al., 2005; 1995) Put simply, viewing another’s action triggers sub-threshold activation of the motor plan to imitate that action (Cooper et al., 2013; Cross et al., 2013) This account is in line with the description of mirror neuron response properties outlined above Namely, the existence of both strictly congruent cells which are sensitive to low-level features of observed actions (direction of motion, viewing angle, effector used, etc.), and more broadly congruent cells that are responsive to a variety of related actions irrespective of the particulars of action performance (Heyes, 2014) A recent review by Cook and colleagues (2014) provides an exhaustive and persuasive account of the evidence supporting the associative view of sensorimotor mirror-neurons Importantly, such congruent action mirroring is reduced following disruption by repetitive TMS over the ventral premotor cortex (part of the core regions of the putative mirror system, Molenberghs et al., 2012) demonstrating the causal role of this region in mirroring for actions (Avenanti et al., 2007) IMITATION AND COUNTER-IMITATION Automatic imitation refers to a particular kind of stimulus-response compatibility effect (SRC effect, Prinz, 1997; Zwickel and Prinz, 2012) in which task-irrelevant action stimuli facilitate the execution of similar actions, and interfere with the execution of dissimilar actions (Heyes, 2011) It is termed ‘automatic’ in so far as it is not dependent on the actor’s intentions, but rather results from long-term sensorimotor connections Automatic imitation has been explained in terms of associative learning which relies on temporal contiguity and contingency; the predictive relationship between stimulus and response (Heyes, 2011) In the same vein, automatic imitation effects are reduced by TMS disruption of the premotor area, highlighting the link between the motor ‘mirror system’ and automatic imitation (Cross et al., 2013) This tendency to match motor plan to action representations is suggested to simply result from the bulk of experiences being of matching gestures, such as communicative gestures like waving in greeting or nodding in agreement As such, the default stimulus-compatible motor plans evoked by action observation are underpinned by mirror representations being forwarded to the primary motor cortex (Rizzolatti and Craighero, 2004) This converges with earlier work from Brass et al (2001) who approached the tendency to imitate from an alternative angle, seeing the response-time bias as an imitation-inhibition effect resulting in longer response latency With participants performing a simple predefined finger-movement at the onset of congruent or incongruent an action stimulus, the incidentally mismatching ‘counter-imitation’ trials were found to reliably activate lateral prefrontal regions important for response inhibition This reframing of mirroring in terms of inhibitory control points to the necessity of adaptable stimulus-response mappings within the putative human mirror system The temporoparietal junction (TPJ) has been implicated in the inhibition of automatic imitation by both neuroimaging (e.g Brass, Ruby & Spengler 2009; Marsh et al 2016) and neuro-stimulation studies Hogeveen and colleagues (2014) applied transcranial direct current stimulation (tDCS) to either the IFC (inferior frontal cortex) or TPJ, versus a sham stimulation control group, and found distinct behavioural effects Imitation inhibition was manipulated (compatible/incompatible actions versus effectors) in a behavioural task and a separate social interaction task coded instances of social mimicry during a participant’s interaction with a confederate TPJ stimulation, hence increased neural excitability, was correlated with increased imitation inhibition, but no change in responses to effector compatibility or social mimicry This was distinct from IFC stimulation which was related to increased social mimicry Although this study is laudable for introducing a naturalistic social mimicry task, the attribution of tDCS effects to specific regions is questionable given the poor spatial resolution of tDCS as compared with TMS, as the authors themselves note Sowden and Catmur (2015) disrupted the right TPJ functioning with repetitive TMS and measured a decrease in the ability to inhibit the tendency to imitate irrelevant actions This was taken to implicate the TPJ as having a casual role in the control of imitation Further corroborating evidence comes from a recent fMRI study by Marsh, Bird and Catmur (2016) examining the modulation of imitation by social factors (mere-group membership and eye gaze) The TPJ was shown to be more engaged during imitatively incompatible than compatible trails and that this was immune to modulation by social factors These studies revolve around predefined action execution and task-irrelevant action observation, rather than intentionally non-imitative responses It is easy to think of many everyday situations where imitating others would be counterproductive, such as catching a ball thrown towards you or having a mug handed to you (precision grip if offered handle-first versus wide grasp for holding the body of the mug, (Newman-Norlund et al., 2007; van Schie et al., 2008) In situations of complementary and joint-actions, the interaction between action-perception and action-preparation is more complicated than direct matching, or ‘mirroring’, would imply Indeed, several studies have reported fMRI evidence of ‘mirror’ activity during non-imitative action Newman-Norland and colleagues (2007) reported that complementary (i.e non-matching) responses provoked greater activation in putative ‘mirror system’ areas than imitative response Complementary object-directed actions (precision grip versus wide grip) were performed across different task-set contexts: preparing imitative or complementary responses This finding was clarified by Ocampo and colleagues (2011) who employed the equivalent task: reaching to grasp a wine glass at the stem or bowl, hence differing in precision of the grip Obviously, in a realworld situation of being handed a wine glass, the complementary grip to that of the observed action would be the most suitable response (e.g if the glass were passed by holding the stem, one would reach with a power grip for the bowl of the glass rather than a precision grip used to hold the stem) The addition of non-action, spatial compatibility manipulations (arrow cues in in/congruent directions relative to responses), allowed for compatibility effects specific to action-stimuli to be isolated (Ocampo et al., 2011) This highlighted the role of the inferior parietal lobe (IPL) and inferior frontal gyrus (IFG) IFG and IPL activations varied relative to the similarity between observed and executed actions, and were postulated to mediate non-imitative responses which may underpin joint-actions and inter-actor cooperation These studies highlight the importance of investigating action execution/observation beyond strictly congruent sensorimotor pairings, and indeed emphasise the real-world relevance of non-imitative responses The flexibility of sensorimotor mirroring for non-imitative contexts has been elegantly scrutinised through non-invasive brain stimulation Cross and Iacoboni (2014a) investigated involuntary, covert imitation within the motor system, with the strategic changes in the degree of motor resonance reflecting the usefulness of imitation in achieving the task at hand MEPs were measured following single-pulse TMS probes while participants prepared to imitate or counter-imitate finger movements presented by video stimuli The imitative compatibility task manipulated the period of preparation before action observation and execution, with participants either cued to prepare an imitative or counter-imitative response, or else given no preparation period until an imperative stimulus was presented Thus the ‘usefulness’ of motor resonance to the task varied: for counter-imitation and no-preparation trials motor resonance would be counter-productive Only in the conditions where preparation to imitate was cued would motor resonance always prime the correct response Cross and Iacoboni (2014a) reported the expected results of showing motor resonance during action observation period, only when the participant had been preparing an imitative response Measured motor resonance was suppressed on trials where participants were preparing to counter-imitate and when the stimulus-response mapping was unknown (nopreparation cue trials) Hence, the tendency for automatic activation of stimulus-compatible responses can be strategically suppressed when this would otherwise interfere with task demands Cross and Iacoboni surmise that this occurs through modulation of mirror system activity Furthermore, by merely emphasising counter-imitation in the task instructions, these mirror-suppression processes are engaged during passive action observation Bardi and colleagues (2015) instructed participants across two sessions to either imitate or counterimitate videos of index or little finger movements, but prior to making any actions, passively observed these stimuli with MEPs recorded to measure muscle-specific excitability Observing actions under the compatible-response instruction showed a typical mirror effect preferential to the muscle which would be involved in performing the observed action Critically, counter-mirror instructions suppressed this pattern, showing that mere instruction can override tendencies for automatic imitative response (Bardi et al., 2015) The adaptability of the mirror system is task-dependent, as evidenced by manipulating the context and task-relevance of counter-mirror responses, and without additional sensorimotor training We argue that this accumulation of evidence suggests an integral role for cognitive control processes integrated with experience-dependent mirroring produces a malleable mirror system COGNITIVE CONTROL REGULATES SENSORIMOTOR MIRRORING Incorporating the associative learning and predictive coding frameworks, sensorimotor mirroring can be viewed as adaptively utilising the representation of external action stimuli to efficiently inform the motor planning of optimal responses Predictions of stimulus-response pairings are based on the prior experience of the action-response which has most often been related to a given action-stimulus (Cross et al., 2013; Cross and Iacoboni, 2014a; 2014b) The missing ingredient is then how such sensorimotor associations are up or down regulated to suit current task demands A past review (Chong and Mattingley, 2008) has examined research relating specifically to selective attention and mirroring, and concluded that such interactions were relatively unexplored, and this largely remains the case Nevertheless through converging evidence from patient studies and fMRI data, Chong and Mattingley (2008) highlighted the importance of prefrontal regions in imitation inhibition, concluding that the frontoparietal mirror system ought to be viewed as mutually informed by wider networks rather than mere automatic visual-to-motor mapping More recently, the involvement of domain-general cognitive control processes has been proposed both in preparatory (Cross and Iacoboni, 2014a) and reactive modulation of mirroring (Cross et al., 2013) Cross and colleagues have framed modulation of stimulus-response mapping in terms of stimulus-response compatibility (SRC) effects within the dual-route model proposed by Braver (2012) Firstly, an automatic fast route links stimulus-compatible responses reflecting long-term associations Secondly, a parallel intentional indirect route links stimulus and response according to temporary rules meeting the current demands For action observation to action execution mapping, the automatic fast route represents compatible, imitative responses enlisted to copy the observed action However in order to counter-imitate an observed action, this automatic route must be suppressed to allow the slower taskrelative, intentional route to prepare the correct stimulus-incompatible response Using fMRI to investigate this model, Cross et al (2014a) had participants perform an counter-imitation task in response to either biological motion stimuli (a video of a hand making finger lifting actions), or a ‘non’ biological cue (two moving dots) The areas found to be involved in stimulus-general preparatory suppression (that is, the intentional indirect route) included left dorso-lateral pre-frontal cortex, frontal pole, posterior parietal cortex and early visual regions (Cross and Iacoboni, 2014b) Importantly, the details of whether this reflects a top-down biasing of visual input to the mirror system or rather a suppression of the motor matchedrepresentation are not discernible from these results Part of this picture has been illuminated by Sasaki and colleagues (2012), who applied dynamic causal modelling (DCM) to ‘mirroring’ activity with a very targeted focus on effective connectivity between the STS and ventral premotor cortex (vPM) They have proposed an inverse internal model linking the STS to vPM, converting visual representations into a motor plan In their view the reverse connection, vPM to STS, forms a forward internal model, translating motor plans into the sensory outcomes of executed actions Thus the putative mirror system is proposed as a dynamic feedback system during action observation for prior associations to prime likely responses These findings align with the description of automatic imitation inhibition in terms of either input or output modulation (Heyes, 2011) Input modulation refers to mediating the processing of action stimuli; whether the motor activations associated with this input is inhibited or permitted to influences overt motor responses is output modulation Essentially, attentional effects modulate input while social cognitive factors relate to output modulation (see Heyes 2011 for a more extensive review of automatic imitation) By incorporating domain-general executive functions into this view of mirroring, mirror activity can be modulated by top-down control relative to current task demands Thereby allow for adaptable stimulus-response mappings within a dynamic mirror system, rather than purely passive and automatic processes Where effortful task-dependent processing of stimulus-response pairs is necessary, higher order, domain-general functions may be recruited to modulate the mirror system’s representation of actions Cognitive control is subserved by interrelated brain regions, organised into two dissociable components (Dosenbach et al., 2008; Nomura et al., 2010) Initiation and rapid moment-to-moment adjustment of control engages a ‘fronto-parietal’ network while longer goal-maintenance for the duration of a task is supported by the ‘cingulo-opercular’ component These two networks are distinguished both by resting-state connectivity, and by double-dissociations in lesion related impairments being restricted to either network (Nomura et al., 2010) Further to being a region in this dual-network of cognitive control, the anterior cingulate cortex (ACC) has been highlighted as critical for conflict detection and error-related processes Of particular relevance to counter-imitation and dynamic mirroring is a purported role of the ACC in detecting conflicts between competing simultaneous representations (Carter and van Veen, 2007) Importantly, conflict detection by the ACC occurs in conjunction with moment-to-moment modulatory control by the dorsolateral prefrontal cortex (dlPFC), in what is referred to as a conflict-control loop Imitation and counter-imitation require such dynamic adjustment of control depending on conflict between internal and external action representations We propose that top-down processes are engaged more by the effortful contradiction of a learnt stimulus-response association, as in counter-imitation, than in simply imitating observed actions, even intentionally In those situations where the salient stimulus is another agent’s action, the mirror system is expected to be recruited to represent the perceived action of others in terms of the same motor codes as used for internally generated motor planning, as a matter of efficiency Where there is conflict between the incoming motor representations and internal action plan (as is the case for incidentally incongruent stimulus-response contexts), conflict detection will be engaged responsively Moreover, when tasked with actively opposing an observed action, conflict detection and response selection processes may be engaged in preparation; i.e in advance of viewing the action stimulus rather than in reaction to it (Cross and Iacoboni, 2014b) This enables the task of encoding of the action stimulus and planning the countering action to be achieved; concurrently holding two contradictory action representations at the time of observation and response planning As compared to incidentally matched or mismatched stimulus-response action pairs, intentional imitation or counter-imitation means the action stimulus is salient to response preparation This context and task-relevant input is actively encoded through wider recruitment of top-down cognitive control networks Repeated contingent experience of a stimulus-response pair (regardless of whether they are congruent, incongruent or complementary) will lead to the automatic pairing (as per associative sequence learning account (Catmur et al., 2009) Henceforth this acquired sensorimotor association (learnt ‘mirror response’) will require task-dependent modulation should it contradict the current task-set In the right context, counter-imitation can become automatic, thereby allowing for less recruitment of executive control functions, especially in incidental stimulus-response mapping Via integration of context cues and goalmaintenance processes, the sensorimotor mirror system would theoretically acquire multiple and opposing associations which are context-dependent Thus cognitive control processes can be engaged to work harmoniously with more automatic sensory-to-action associations (‘mirroring’) to allow for adaptive behaviour CONCLUSIONS The mirror system underlying motor resonance is not exclusively involved in stimulus-toresponse matching Rather the association of related but dissimilar stimulus-response pairs when they occur repeatedly together, allows for variable sensorimotor mapping Indeed viewed as part of a wider action observation network, the mirror system is active during the preparation of complementary actions as well as stimulus-matched responses (NewmanNorlund et al., 2007; 2008; Ocampo et al., 2011) We consider mirroring to be a property that is acquired through associating contingent experiences, of internally and externally driven representations, and that brain areas with neurons exhibiting this property may contribute to a wide range of higher-order processes (e.g understanding intention, social interaction) without necessarily having evolved specifically for these functions (Catmur, 2012) In the right context a non-imitative response can become the automatic response to an action stimulus, given the acquisition of mirror system representations (Catmur, Walsh, & Heyes, 2009; Keysers, & Gazzola, 2014) and their malleability via training (Catmur et al 2008; Heyes et al, 2013) Indeed, should a particular stimulus-response pair be well learned, a reduction in the reliance on top-down control would indicate its automaticity over other less frequently experienced responses Hence, mirror processes must be regarded as functioning within a dynamic system that is task- and experience-dependent, rather than fixed To this end, the integration of mirroring with domain-general and higher-order processes, including cognitive control, is a necessary direction for mirror neuron research to take For example, a novice dancer carefully observing the movement of their partner and performing a complementary action requires fluid interplay between cognitive control and mirror system processes With practice this observed-executed action pair becomes less effortful and relies less on response-selection or goal-maintenance, and rather the two actions become tightly associated by repeated pairing and co-activate the mirror system within that context It remains unclear at which points within mirror networks modulation by top-down feedback occurs, nor exactly how this changes with learning We see the current trend towards a systems neuroscience approaches, rather than a focus on functional specialisation, is well suited to examining such modulation of sensorimotor mirroring Mirroring should be framed within hierarchical networks including frontal regions associated with response-selection and goal maintenance Ultimately, the demands upon the human mirror system engendered by the complexity of human interactions necessitates that sensorimotor representations within this system are adjustable, and not simply set to a mirror-matched default for imitating everyone’s actions ACKNOWLEDGEMENTS The authors research is funded by the Australian Research Council Special Research Initiative (SR12030015) Science of Learning Research Centre REFERENCES Avenanti, A., Bolognini, N., Maravita, A., Aglioti, S.M., 2007 Somatic and motor components of action simulation Current Biology 17, 2129–2135 doi:DOI 10.1016/j.cub.2007.11.045 Baldissera, F., Cavallari, P., Craighero, L., Fadiga, L., 2001 Modulation of spinal excitability during observation of hand actions in humans Eur J Neurosci 13, 190–194 doi:10.1046/j.0953-816x.2000.01368.x Bardi, L., Bundt, C., Notebaert, W., Brass, M., 2015 Eliminating mirror responses by instructions Cortex doi:10.1016/j.cortex.2015.04.018 Bonini, L., Ferrari, P.F., 2011 Evolution of mirror systems: a simple mechanism for complex cognitive functions Ann N Y Acad Sci 1225, 166–175 doi:10.1111/j.17496632.2011.06002.x Botvinick, M.M., Braver, T.S., Barch, D.M., Carter, C.S., Cohen, J.D., 2001 Conflict monitoring and cognitive control Psychol Rev 108, 624–652 Brass, M., Zysset, S., Cramon, von, D.Y., 2001 The inhibition of imitative response tendencies NeuroImage 14, 1416–1423 doi:10.1006/nimg.2001.0944 Brass, M., Heyes, C., 2005 Imitation: is cognitive neuroscience solving the correspondence problem? Trends in Cognitive Sciences 9, 489–495 doi:10.1016/j.tics.2005.08.007 Brass, M., Ruby, P., Spengler, S., 2009 Inhibition of imitative behaviour and social cognition Philosophical Transactions of the Royal Society of London B: Biological Sciences 364, 2359–2367 doi:10.1098/rstb.2009.0066 Braver, T.S., 2012 The variable nature of cognitive control: a dual mechanisms framework Trends in Cognitive Sciences 16, 106–113 doi:10.1016/j.tics.2011.12.010 Carter, C.S., van Veen, V., 2007 Anterior cingulate cortex and conflict detection: An update of theory and data Cognitive, Affective, & Behavioral Neuroscience 7, 367–379 doi:10.3758/CABN.7.4.367 Casile, A., 2013 Mirror neurons (and beyond) in the macaque brain: An overview of 20 years of research Neuroscience letters 540, 3–14 doi:10.1016/j.neulet.2012.11.003 Casile, A., Caggiano, V., Ferrari, P.F., 2011 The Mirror Neuron System: A Fresh View The Neuroscientist 17, 524–538 doi:10.1177/1073858410392239 Catmur, C., 2012 Sensorimotor learning and the ontogeny of the mirror neuron system Neuroscience letters Catmur, C., Walsh, V., Heyes, C., 2009 Associative sequence learning: the role of experience in the development of imitation and the mirror system Philos Trans R Soc Lond., B, Biol Sci 364, 2369–2380 doi:10.1098/rstb.2009.0048 Catmur, C., Walsh, V., Heyes, C., 2007 Sensorimotor Learning Configures the Human Mirror System Current Biology 17, 1527–1531 doi:10.1016/j.cub.2007.08.006 Chong, T.T.J., Cunnington, R., Williams, M.A., Kanwisher, N., Mattingley, J.B., 2008 fMRI Adaptation Reveals Mirror Neurons in Human Inferior Parietal Cortex Current Biology 18, 1576–1580 doi:10.1016/j.cub.2008.08.068 Chong, T.T.J., Mattingley, J.B., 2008 Automatic and Controlled Processing within the Mirror Neuron System, in: Pineda, J.A (Ed.), Mirror Neuron Systems Humana Press, Totowa, NJ, pp 213–233 doi:10.1007/978-1-59745-479-7_10 Clark, S., Tremblay, F., Ste-Marie, D., 2004 Differential modulation of corticospinal excitability during observation, mental imagery and imitation of hand actions Neuropsychologia 42, 105–112 doi:10.1016/S0028-3932(03)00144-1 Cook, R., Bird, G., 2013 Do mirror neurons really mirror and they really code for action goals? Cortex 49, 2944–2945 doi:10.1016/j.cortex.2013.05.006 Cook, R., Bird, G., Catmur, C., Press, C., Heyes, C., 2014 Mirror neurons: From origin to function Behav Brain Sci 37, 177–192 doi:10.1017/S0140525X13000903 Cooper, R.P., Cook, R., Dickinson, A., Heyes, C.M., 2013 Associative (not Hebbian) learning and the mirror neuron system Neuroscience letters 540, 28–36 doi:10.1016/j.neulet.2012.10.002 Cross, K.A., Iacoboni, M., 2014a To imitate or not: Avoiding imitation involves preparatory inhibition of motor resonance NeuroImage 91, 288–236 Cross, K.A., Iacoboni, M., 2014b Neural systems for preparatory control of imitation Philos Trans R Soc Lond., B, Biol Sci 369, 20130176–20130176 doi:10.1016/j.bbr.2008.08.028 Cross, K.A., Torrisi, S., Losin, E., Iacoboni, M., 2013 Controlling automatic imitative tendencies: interactions between mirror neuron and cognitive control systems NeuroImage di Pellegrino, G., Fadiga, L., Fogassi, L., Gallese, V., Rizzolatti, G., 1992 Understanding motor events: a neurophysiological study Experimental Brain Research 91, 176–180 Dinstein, I., Hasson, U., Rubin, N., Heeger, D.J., 2007 Brain areas selective for both observed and executed movements J Neurophysiol 98, 1415–1427 doi:10.1152/jn.00238.2007 Dosenbach, N.U.F., Fair, D.A., Cohen, A.L., Schlaggar, B.L., Petersen, S.E., 2008 A dualnetworks architecture of top-down control Trends in Cognitive Sciences 12, 99–105 doi:10.1016/j.tics.2008.01.001 Fadiga, L., Craighero, L., Olivier, E., 2005 Human motor cortex excitability during the perception of others' action Current Opinion in Neurobiology 15, 213–218 doi:10.1016/j.conb.2005.03.013 Fadiga, L., Fogassi, L., Pavesi, G., Rizzolatti, G., 1995 Motor facilitation during action observation: a magnetic stimulation study J Neurophysiol 73, 2608–2611 Ferrari, P.F., Gallese, V., Rizzolatti, G., Fogassi, L., 2003 Mirror neurons responding to the observation of ingestive and communicative mouth actions in the monkey ventral premotor cortex Eur J Neurosci 17, 1703–1714 Ferrari, P.F., Tramacere, A., Simpson, E.A., Iriki, A., 2013 Mirror neurons through the lens of epigenetics Trends in Cognitive Sciences 17, 450–457 doi:10.1016/j.tics.2013.07.003 Gallese, V., Fadiga, L., Fogassi, L., Rizzolatti, G., 1996 Action recognition in the premotor cortex Brain 119 (Pt 2), 593–609 Giudice, M.D., Manera, V., Keysers, C., 2009 Programmed to learn? The ontogeny of mirror neurons Developmental Science 12, 350–363 doi:10.1111/j.1467-7687.2008.00783.x Heyes, C., 2014 Tinbergen on mirror neurons Philos Trans R Soc Lond., B, Biol Sci 369, 20130180–20130180 doi:10.1111/j.1460-9568.2007.05682.x Heyes, C., 2013 A new approach to mirror neurons: Developmental history, system-level theory and intervention experiments Cortex 49, 2946–2948 doi:10.1016/j.cortex.2013.07.002 Heyes, C., 2011 Automatic imitation Psychological bulletin 137, 463 Heyes, C., 2010a Where mirror neurons come from? Neuroscience and Biobehavioral Reviews 34, 575–583 doi:10.1016/j.neubiorev.2009.11.007 Heyes, C., 2010b Mesmerising mirror neurons NeuroImage 51, 789–791 doi:10.1016/j.neuroimage.2010.02.034 Heyes, C., 2016 Imitation: Not in Our Genes Current Biology 26, R412–R414 doi:10.1016/j.cub.2016.03.060 Hickok, G., 2013 Do mirror neurons subserve action understanding? Neuroscience letters 540, 56–58 doi:10.1016/j.neulet.2012.11.001 Hickok, G., 2009 Eight problems for the mirror neuron theory of action understanding in monkeys and humans Journal of Cognitive Neuroscience 21, 1229–1243 doi:10.1162/jocn.2009.21189 Hickok, G., Hauser, M., 2010 (Mis)understanding mirror neurons Curr Biol 20, R593–4 doi:10.1016/j.cub.2010.05.047 Hogeveen, J., Obhi, S.S., Banissy, M.J., Santiesteban, I., Press, C., Catmur, C., Bird, G., 2014 Task-dependent and distinct roles of the temporoparietal junction and inferior frontal cortex in the control of imitation Social Cognitive and Affective Neuroscience 10, nsu148–1009 doi:10.1093/scan/nsu148 Keysers, C., Gazzola, V., 2014 Hebbian learning and predictive mirror neurons for actions, sensations and emotions Philos Trans R Soc Lond., B, Biol Sci 369, 20130175– 20130175 doi:10.1016/S1364-6613(98)01262-5 Keysers, C., Gazzola, V., 2009 Expanding the mirror: vicarious activity for actions, emotions, and sensations Current Opinion in Neurobiology 19, 666–671 doi:10.1016/j.conb.2009.10.006 Keysers, C., Perrett, D.I., 2004 Demystifying social cognition: a Hebbian perspective Trends in Cognitive Sciences 8, 501–507 doi:10.1016/j.tics.2004.09.005 Kilner, J.M., Friston, K.J., Frith, C.D., 2007a Predictive coding: an account of the mirror neuron system Cogn Process 8, 159–166 doi:10.1007/s10339-007-0170-2 Kilner, J.M., Friston, K.J., Frith, C.D., 2007b The mirror-neuron system: a Bayesian perspective Neuroreport 18, 619–623 doi:10.1097/WNR.0b013e3281139ed0 Kilner, J.M., Lemon, R.N., 2013 What We Know Currently about Mirror Neurons Current Biology 23, R1057–R1062 doi:10.1016/j.cub.2013.10.051 Kilner, J.M., Neal, A., Weiskopf, N., Friston, K.J., Frith, C.D., 2009 Evidence of mirror neurons in human inferior frontal gyrus Journal of Neuroscience 29, 10153–10159 doi:10.1523/JNEUROSCI.2668-09.2009 Kilner, J.M., Paulignan, Y., Blakemore, S.J., 2003 An interference effect of observed biological movement on action Current Biology 13, 522–525 doi:10.1016/S09609822(03)00165-9 Koechlin, E., Ody, C., Kouneiher, F., 2003 The architecture of cognitive control in the human prefrontal cortex Science 302, 1181–1185 doi:10.1126/science.1088545 Körding, K.P., Wolpert, D.M., 2004 Bayesian integration in sensorimotor learning Nature 427, 244–247 doi:10.1038/nature02169 Kraskov, A., Dancause, N., Quallo, M.M., Shepherd, S., Lemon, R.N., 2009 Corticospinal neurons in macaque ventral premotor cortex with mirror properties: a potential mechanism for action suppression? Neuron 64, 922–930 doi:10.1016/j.neuron.2009.12.010 Kraskov, A., Philipp, R., Waldert, S., Vigneswaran, G., Quallo, M.M., Lemon, R.N., 2014 Corticospinal mirror neurons Philos Trans R Soc Lond., B, Biol Sci 369, 20130174– 20130174 doi:10.1523/JNEUROSCI.0487-08.2008 Krekelberg, B., Boynton, G.M., van Wezel, R.J.A., 2006 Adaptation: from single cells to BOLD signals Trends Neurosci 29, 250–256 doi:10.1016/j.tins.2006.02.008 Larsson, J., Smith, A.T., 2012 fMRI Repetition Suppression: Neuronal Adaptation or Stimulus Expectation? Cerebral Cortex 22, 567–576 doi:10.1093/cercor/bhr119 Lepage, J.-F., Théoret, H., 2007 The mirror neuron system: grasping others' actions from birth? Developmental Science 10, 513–523 doi:10.1111/j.1467-7687.2007.00631.x Lingnau, A., Gesierich, B., Caramazza, A., 2009 Asymmetric fMRI adaptation reveals no evidence for mirror neurons in humans Proceedings of the National Academy of Sciences 106, 9925–9930 doi:10.1073/pnas.0902262106 Marsh, L.E., Bird, G., Catmur, C., 2016 The imitation game: Effects of social cues on “imitation” are domain-general in nature NeuroImage 139, 368–375 doi:10.1016/j.neuroimage.2016.06.050 Meltzoff, A.N., Moore, M.K., 1977 Imitation of facial and manual gestures by human neonates Science 198, 75–78 doi:10.1126/science.198.4312.75 Meltzoff, A.N., Moore, M.K., 1989 Imitation in newborn infants: Exploring the range of gestures imitated and the underlying mechanisms Developmental Psychology 25, 954 doi:10.1037/0012-1649.25.6.954 Meltzoff, A.N., 2002 Imitation as a mechanism of social cognition: Origins of empathy, theory of mind, and the representation of action, in: Goswami, U (Ed.), Blackwell Handbook of Childhood Cognitive Development Blackwell Publishers, Oxford, pp 6-25 Miller, E.K., Cohen, J.D., 2003 An integrative theory prefrontal cortex function http://dx.doi.org.ezproxy.library.uq.edu.au/10.1146/annurev.neuro.24.1.167 24, 167– 202 doi:10.1146/annurev.neuro.24.1.167 Molenberghs, P., Cunnington, R., Mattingley, J.B., 2012 Neuroscience and Biobehavioral Reviews Neuroscience and Biobehavioral Reviews 36, 341–349 doi:10.1016/j.neubiorev.2011.07.004 Mukamel, R., Ekstrom, A.D., Kaplan, J., Iacoboni, M., Fried, I., 2010 Single-neuron responses in humans during execution and observation of actions Curr Biol 20, 750– 756 doi:10.1016/j.cub.2010.02.045 Newman-Norlund, R.D., Bosga, J., Meulenbroek, R.G.J., Bekkering, H., 2008 Anatomical substrates of cooperative joint-action in a continuous motor task: virtual lifting and balancing NeuroImage 41, 169–177 doi:10.1016/j.neuroimage.2008.02.026 Newman-Norlund, R.D., van Schie, H.T., van Zuijlen, A.M.J., Bekkering, H., 2007 The mirror neuron system is more active during complementary compared with imitative action Nat Neurosci 10, 817–818 doi:10.1038/nn1911 Nomura, E.M., Gratton, C., Visser, R.M., Kayser, A., Perez, F., D'Esposito, M., 2010 Double dissociation of two cognitive control networks in patients with focal brain lesions Proceedings of the National Academy of Sciences 107, 12017–12022 Ocampo, B., Kritikos, A., Cunnington, R., 2011 How frontoparietal brain regions mediate imitative and complementary actions: an FMRI study PLoS ONE 6, e26945 doi:10.1371/journal.pone.0026945 Oostenbroek, J., Suddendorf, T., Nielsen, M., Redshaw, J., Kennedy-Costantini, S., Davis, J., Clark, S., Slaughter, V., 2016 Comprehensive Longitudinal Study Challenges the Existence of Neonatal Imitation in Humans Current Biology 26, 1334–1338 doi:10.1016/j.cub.2016.03.047 Press, C., Weiskopf, N., Kilner, J.M., 2012 Dissociable roles of human inferior frontal gyrus during action execution and observation NeuroImage 60, 1671–1677 doi:10.1016/j.neuroimage.2012.01.118 Prinz, W., 1997 Perception and Action Planning European Journal of Cognitive Psychology 9, 129–154 doi:10.1080/713752551 Ridderinkhof, K.R., van den Wildenberg, W.P.M., Segalowitz, S.J., Carter, C.S., 2004 Neurocognitive mechanisms of cognitive control: The role of prefrontal cortex in action selection, response inhibition, performance monitoring, and reward-based learning Brain and Cognition 56, 129–140 doi:10.1016/j.bandc.2004.09.016 Rizzolatti, G., Craighero, L., 2004 The Mirror Neuron System Annu Rev Neurosci 27, 169–192 doi:10.1146/annurev.neuro.27.070203.144230 Rizzolatti, G., Fogassi, L., 2014 The mirror mechanism: recent findings and perspectives Philosophical Transactions of the Royal Society of London B: Biological Sciences 369 Sasaki, A.T., Kochiyama, T., Sugiura, M., Tanabe, H.C., Sadato, N., 2012 Neural networks for action representation: a functional magnetic-resonance imaging and dynamic causal modeling study Front Hum Neurosci 6, 236 doi:10.3389/fnhum.2012.00236 van Schie, H.T., van Waterschoot, B.M., Bekkering, H., 2008 Understanding action beyond imitation: Reversed compatibility effects of action observation in imitation and joint action J Exp Psychol Hum Percept Perform 34, 1493–1500 doi:10.1037/a0011750 Sowden, S., Catmur, C., 2015 The role of the right temporoparietal junction in the control of imitation Cerebral Cortex 25, 1107–1113 doi:10.1093/cercor/bht306 Wolpert, D.M., Diedrichsen, J., Flanagan, J.R., 2011 Principles of sensorimotor learning Nat Rev Neurosci 12, 739–751 doi:10.1038/nrn3112 Wolpert, D.M., Landy, M.S., 2012 Motor control is decision-making Current Opinion in Neurobiology 22, 996–1003 doi:10.1016/j.conb.2012.05.003 Zwickel, J., Prinz, W., 2012 Assimilation and contrast: the two sides of specific interference between action and perception Psychol Res 76, 171–182 doi:10.1007/s00426-0110338-3 .. .MORE THAN AN IMITATION GAME: TOP- DOWN MODULATION OF THE HUMAN MIRROR SYSTEM Literature Review Megan E J Campbell1 and Ross Cunnington1,2 The Queensland Brain Institute, School of Psychology,... system much of the nuanced variability in the response properties of mirror neurons has been glossed over 2.2 A MIRROR SYSTEM IN THE HUMAN BRAIN The existence of mirror neurons in humans is broadly... representations of actions and the motor programs which generate them (Catmur, 2012; Catmur et al., 2007; Hickok, 2009) Another general limitation of many of the human imaging studies reporting mirror