Predicting the Future: Mirror Neurons Reflect the Intentions of Others.
PLoS Biol. 2005 Mar;3(3):1. [Abstract] [Full Text]

Iacoboni M, Molnar-Szakacs I, Gallese V, Buccino G, Mazziotta JC, Rizzolatti G
Grasping the intentions of others with one's own mirror neuron system.
PLoS Biol. 2005 Mar;3(3):e79.
Understanding the intentions of others while watching their actions is a fundamental building block of social behavior. The neural and functional mechanisms underlying this ability are still poorly understood. To investigate these mechanisms we used functional magnetic resonance imaging. Twenty-three subjects watched three kinds of stimuli: grasping hand actions without a context, context only (scenes containing objects), and grasping hand actions performed in two different contexts. In the latter condition the context suggested the intention associated with the grasping action (either drinking or cleaning). Actions embedded in contexts, compared with the other two conditions, yielded a significant signal increase in the posterior part of the inferior frontal gyrus and the adjacent sector of the ventral premotor cortex where hand actions are represented. Thus, premotor mirror neuron areas-areas active during the execution and the observation of an action-previously thought to be involved only in action recognition are actually also involved in understanding the intentions of others. To ascribe an intention is to infer a forthcoming new goal, and this is an operation that the motor system does automatically. [Abstract] [Full Text]

Gallese V, Keysers C, Rizzolatti G
A unifying view of the basis of social cognition.
Trends Cogn Sci. 2004 Sep;8(9):396-403.
In this article we provide a unifying neural hypothesis on how individuals understand the actions and emotions of others. Our main claim is that the fundamental mechanism at the basis of the experiential understanding of others' actions is the activation of the mirror neuron system. A similar mechanism, but involving the activation of viscero-motor centers, underlies the experiential understanding of the emotions of others. [Abstract]

Fadiga L, Craighero L, Olivier E
Human motor cortex excitability during the perception of others' action.
Curr Opin Neurobiol. 2005 Apr;15(2):213-8.
Neuroscience research during the past ten years has fundamentally changed the traditional view of the motor system. In monkeys, the finding that premotor neurons also discharge during visual stimulation (visuomotor neurons) raises new hypotheses about the putative role played by motor representations in perceptual functions. Among visuomotor neurons, mirror neurons might be involved in understanding the actions of others and might, therefore, be crucial in interindividual communication. Functional brain imaging studies enabled us to localize the human mirror system, but the demonstration that the motor cortex dynamically replicates the observed actions, as if they were executed by the observer, can only be given by fast and focal measurements of cortical activity. Transcranial magnetic stimulation enables us to instantaneously estimate corticospinal excitability, and has been used to study the human mirror system at work during the perception of actions performed by other individuals. In the past ten years several TMS experiments have been performed investigating the involvement of motor system during others' action observation. Results suggest that when we observe another individual acting we strongly 'resonate' with his or her action. In other words, our motor system simulates underthreshold the observed action in a strictly congruent fashion. The involved muscles are the same as those used in the observed action and their activation is temporally strictly coupled with the dynamics of the observed action. [Abstract]

Tai YF, Scherfler C, Brooks DJ, Sawamoto N, Castiello U
The human premotor cortex is 'mirror' only for biological actions.
Curr Biol. 2004 Jan 20;14(2):117-20.
Previous work has shown that both human adults and children attend to grasping actions performed by another person but not necessarily to those made by a mechanical device. According to recent neurophysiological data, the monkey premotor cortex contains "mirror" neurons that discharge both when the monkey performs specific manual grasping actions and when it observes another individual performing the same or similar actions. However, when a human model uses tools to perform grasping actions, the mirror neurons are not activated. A similar "mirror" system has been described in humans, but whether or not it is also tuned specifically to biological actions has never been tested. Here we show that when subjects observed manual grasping actions performed by a human model a significant neural response was elicited in the left premotor cortex. This activation was not evident for the observation of grasping actions performed by a robot model commanded by an experimenter. This result indicates for the first time that in humans the mirror system is biologically tuned. This system appears to be the neural substrate for biological preference during action coding. [Abstract]

Wohlschläger A, Haggard P, Gesierich B, Prinz W
The perceived onset time of self- and other-generated actions.
Psychol Sci. 2003 Nov;14(6):586-91.
Awareness of actions is partly based on the intentions accompanying them. Thus, the awareness of self- and other-generated actions should differ to the extent that access to own and other's intentions differs. Recent studies have found a brain circuit (the mirror-neuron system) that represents self- and other-generated actions in an integrated fashion. This system does not respond to actions made by nonagents, such as machines. We measured the estimated onset time of actions that subjects either executed themselves or observed being executed by someone else or by a machine. In three experiments, the estimates of the machine actions always differed from those of self- and other-generated actions, whereas the latter two were indistinguishable. Our results are consistent with the view that intentions are attributed to others but not to machines. They also raise the interesting possibility that people attribute intentions to themselves in the same way as they do to others. [Abstract]

Saxe R
Against simulation: the argument from error.
Trends Cogn Sci. 2005 Apr;9(4):174-9.
According to Simulation Theory, to understand what is going on in another person's mind, the observer uses his or her own mind as a model of the other mind. Recently, philosophers and cognitive neuroscientists have proposed that mirror neurones (which fire in response to both executing and observing a goal directed action) provide a plausible neural substrate for simulation, a mechanism for directly perceiving, or 'resonating' with, the contents of other minds. This article makes the case against Simulation Theory, using evidence from cognitive neuroscience, developmental psychology, and social psychology. In particular, the errors that adults and children make when reasoning about other minds are not consistent with the 'resonance' versions of Simulation Theory. [Abstract] [PDF]

Umiltà MA, Kohler E, Gallese V, Fogassi L, Fadiga L, Keysers C, Rizzolatti G
I know what you are doing. a neurophysiological study.
Neuron. 2001 Jul 19;31(1):155-65.
In the ventral premotor cortex of the macaque monkey, there are neurons that discharge both during the execution of hand actions and during the observation of the same actions made by others (mirror neurons). In the present study, we show that a subset of mirror neurons becomes active during action presentation and also when the final part of the action, crucial in triggering the response in full vision, is hidden and can therefore only be inferred. This implies that the motor representation of an action performed by others can be internally generated in the observer's premotor cortex, even when a visual description of the action is lacking. The present findings support the hypothesis that mirror neuron activation could be at the basis of action recognition. [Abstract]

Blakemore SJ, Frith C
The role of motor contagion in the prediction of action.
Neuropsychologia. 2005;43(2):260-7.
It has been proposed that actions are intrinsically linked to perception [James, W. (1890). Principles of psychology. New York, NY, USA: Holt; Jeannerod M. (1994). The representing brain - neural correlates of motor intention and imagery. Behavioural Brain Sciences, 17, 187-202; Prinz, W. (1997). Perception and action planning. European Journal of Cognitive Psychology, 9, 129-154]. The idea behind these theories is that observing, imagining or in any way representing an action excites the motor programs used to execute that same action. There is neurophysiological evidence that neurons in premotor cortex of monkeys respond both during movement execution and during the observation of goal-directed action ('mirror neurons'). In humans, a proportion of the brain regions involved in executing actions are activated by the mere observation of action (the 'mirror system'). In this paper, we briefly review recent empirical studies of the mirror system, and discuss studies demonstrating interference effects between observed and executed movements. This interference, which might be a form of 'motor contagion', seems to arise specifically from the observation of biological movements, whether or not these movements are goal-directed. We suggest that this crude motor contagion is the first step in a more sophisticated predictive system that allows us to infer goals from the observation of actions. [Abstract]

Buccino G, Binkofski F, Riggio L
The mirror neuron system and action recognition.
Brain Lang. 2004 May;89(2):370-6.
Mirror neurons, first described in the rostral part of monkey ventral premotor cortex (area F5), discharge both when the animal performs a goal-directed hand action and when it observes another individual performing the same or a similar action. More recently, in the same area mirror neurons responding to the observation of mouth actions have been also found. In humans, through an fMRI study, it has been shown that the observation of actions performed with the hand, the mouth and the foot leads to the activation of different sectors of Broca's area and premotor cortex, according to the effector involved in the observed action, following a somatotopic pattern which resembles the classical motor cortex homunculus. These results strongly support the existence of an execution-observation matching system (mirror neuron system). It has been proposed that this system is involved in action recognition. Experimental evidence in favor of this hypothesis both in the monkey and humans are shortly reviewed. [Abstract]

Gangitano M, Mottaghy FM, Pascual-Leone A
Modulation of premotor mirror neuron activity during observation of unpredictable grasping movements.
Eur J Neurosci. 2004 Oct;20(8):2193-202.
Using transcranial magnetic stimulation, we explored the properties of premotor mirror neurons during the passive observation of a reaching-grasping movement in human subjects. Two different experiments were run using video-clips as visual stimuli. Video-clips showed a normally performed (control stimulus) or an anomalous reaching-grasping movement executed by delaying the time of the appearance of the maximal finger aperture (experiment 1), or substituting it with an unpredictable closure (experiment 2). Motor evoked potentials were recorded at different time-points during the observation of the video-clips. Profiles of cortical excitability were drawn and compared with the kinematic profiles of the corresponding movement. Passive observation of the natural movement evoked a profile of cortical excitability that is in concordance with the timing of the kinematic profile of the shown finger movements. Observation of the uncommon movements did not exert any modulation (experiment 1) or evoked an activity that matched, at the beginning, the modulation obtained with observation of the natural movement (experiment 2). Results show that the resonant motor plan is loaded as whole at the beginning of observation and once started tends to proceed to its completion regardless of changes to the visual cues. The results exclude the possibility of a temporal fragmentation of the resonant plan, because activation of different populations of mirror neurons for each phase of the ongoing action. They further support the notion of the role of the mirror system as neural substrate for the observing-execution matching system and extend the current knowledge regarding mechanisms that trigger the internal representation of an action. [Abstract]

Oztop E, Arbib MA
Schema design and implementation of the grasp-related mirror neuron system.
Biol Cybern. 2002 Aug;87(2):116-40.
Mirror neurons within a monkey's premotor area F5 fire not only when the monkey performs a certain class of actions but also when the monkey observes another monkey (or the experimenter) perform a similar action. It has thus been argued that these neurons are crucial for understanding of actions by others. We offer the hand-state hypothesis as a new explanation of the evolution of this capability: the basic functionality of the F5 mirror system is to elaborate the appropriate feedback - what we call the hand state - for opposition-space based control of manual grasping of an object. Given this functionality, the social role of the F5 mirror system in understanding the actions of others may be seen as an exaptation gained by generalizing from one's own hand to an other's hand. In other words, mirror neurons first evolved to augment the "canonical" F5 neurons (active during self-movement based on observation of an object) by providing visual feedback on "hand state," relating the shape of the hand to the shape of the object. We then introduce the MNS1 (mirror neuron system 1) model of F5 and related brain regions. The existing Fagg-Arbib-Rizzolatti-Sakata model represents circuitry for visually guided grasping of objects, linking the anterior intraparietal area (AIP) with F5 canonical neurons. The MNS1 model extends the AIP visual pathway by also modeling pathways, directed toward F5 mirror neurons, which match arm-hand trajectories to the affordances and location of a potential target object. We present the basic schemas for the MNS1 model, then aggregate them into three "grand schemas" - visual analysis of hand state, reach and grasp, and the core mirror circuit - for each of which we present a useful implementation (a non-neural visual processing system, a multijoint 3-D kinematics simulator, and a learning neural network, respectively). With this implementation we show how the mirror system may learn to recognize actions already in the repertoire of the F5 canonical neurons. We show that the connectivity pattern of mirror neuron circuitry can be established through training, and that the resultant network can exhibit a range of novel, physiologically interesting behaviors during the process of action recognition. We train the system on the basis of final grasp but then observe the whole time course of mirror neuron activity, yielding predictions for neurophysiological experiments under conditions of spatial perturbation, altered kinematics, and ambiguous grasp execution which highlight the importance of the timing of mirror neuron activity. [Abstract]

Fogassi L, Gallese V, Buccino G, Craighero L, Fadiga L, Rizzolatti G
Cortical mechanism for the visual guidance of hand grasping movements in the monkey: A reversible inactivation study.
Brain. 2001 Mar;124(Pt 3):571-86.
Picking up an object requires two basic motor operations: reaching and grasping. Neurophysiological studies in monkeys have suggested that the visuomotor transformations necessary for these two operations are carried out by separate parietofrontal circuits and that, for grasping, a key role is played by a specific sector of the ventral premotor cortex: area F5. The aim of the present study was to test the validity of this hypothesis by reversibly inactivating area F5 in monkeys trained to grasp objects of different shape, size and orientation. In separate sessions, the hand field of the primary motor cortex (area F1 or area 4) was also reversibly inactivated. The results showed that after inactivation of area F5 buried in the bank of the arcuate sulcus (the F5 sector where visuomotor neurones responding to object presentation are located), the hand shaping preceding grasping was markedly impaired and the hand posture was not appropriate for the object size and shape. The monkeys were eventually able to grasp the objects, but only after a series of corrections made under tactile control. With small inactivations the deficits concerned the contralesional hand, with larger inactivations the ipsilateral hand as well. In addition, there were signs of peripersonal neglect in the hemispace contralateral to the inactivation site. Following inactivation of area F5 lying on the cortical convexity (the F5 sector where visuomotor neurones responding to action observation, 'mirror neurones', are found) only a motor slowing was observed, the hand shaping being preserved. The inactivation of the hand field of area F1 produced a severe paralysis of contralateral finger movements with hypotonia. The results of this study indicate the crucial role of the ventral premotor cortex in visuomotor transformations for grasping movements. More generally, they provide strong support for the notion that distal and proximal movement organization relies upon distinct cortical circuits. Clinical data on distal movement deficits in humans are re-examined in the light of the present findings. [Abstract] [Full Text]

Gallese V, Keysers C, Rizzolatti G
A unifying view of the basis of social cognition.
Trends Cogn Sci. 2004 Sep;8(9):396-403.
In this article we provide a unifying neural hypothesis on how individuals understand the actions and emotions of others. Our main claim is that the fundamental mechanism at the basis of the experiential understanding of others' actions is the activation of the mirror neuron system. A similar mechanism, but involving the activation of viscero-motor centers, underlies the experiential understanding of the emotions of others. [Abstract]

Grèzes J, Armony JL, Rowe J, Passingham RE
Activations related to "mirror" and "canonical" neurones in the human brain: an fMRI study.
Neuroimage. 2003 Apr;18(4):928-37.
In the macaque monkey ventral premotor cortex (F5), "canonical neurones" are active when the monkey observes an object and when the monkey grasps that object. In the same area, "mirror neurones" fire both when the monkey observes another monkey grasping an object and when the monkey grasps that object. We used event-related fMRI to investigate where in the human brain activation can be found that reflects both canonical and mirror neuronal activity. There was activation in the intraparietal and ventral limbs of the precentral sulcus when subjects observed objects and when they executed movements in response to the objects (canonical neurones). There was activation in the dorsal premotor cortex, the intraparietal cortex, the parietal operculum (SII), and the superior temporal sulcus when subjects observed gestures (mirror neurones). Finally, activations in the ventral premotor cortex and inferior frontal gyrus (area 44) were found when subjects imitated gestures and executed movements in response to objects. We suggest that in the human brain, the ventral limb of the precentral sulcus may form part of the area designated F5 in the macaque monkey. It is possible that area 44 forms an anterior part of F5, though anatomical studies suggest that it may be a transitional area between the premotor and prefrontal cortices. [Abstract]

Rizzolatti G, Fadiga L
Grasping objects and grasping action meanings: the dual role of monkey rostroventral premotor cortex (area F5).
Novartis Found Symp. 1998;21881-95; discussion 95-103.
Monkey area F5 consists of two main histochemical sectors, one buried inside the arcuate sulcus, the other located on the cortical convexity. Neurons of both sectors discharge during hand movements. Many of them also fire in response to the presentation of visual stimuli. However, the visual stimuli effective for triggering the neurons in each sector are markedly different. Neurons located in the bank of the arcuate sulcus respond to the observation of 3D objects, provided that object size and shape is congruent with the prehension type coded by the neuron ('canonical' F5 neurons). Neurons of the convexity discharge when the monkey observes hand actions performed by another individual, provided that they are similar to the motor action coded by the neuron ('mirror' neurons). What do the canonical F5 neurons and the surprising mirror neurons have in common? The interpretation we propose is that these two categories of F5 neurons both generate an internal copy of a potential hand action. In the case of 'canonical' neurons, this copy gives a description of how to grasp an object; in the case of mirror neurons it gives a description of an action made by another person. Because the individuals know the consequences of their actions, we propose that the internal motor copies of the observed actions represent the neural basis for understanding the meaning of actions made by others. [Abstract]

Nishitani N, Hari R
Temporal dynamics of cortical representation for action.
Proc Natl Acad Sci U S A. 2000 Jan 18;97(2):913-8.
Brain-imaging studies have shown that the human Broca's region and precentral motor cortex are activated both during execution of hand actions and during observation of similar actions performed by other individuals. We aimed to clarify the temporal dynamics of this cortical activation by neuromagnetic recordings during execution, on-line imitation, and observation of right-hand reaching movements that ended with a precision pinch of the tip of a manipulandum. During execution, the left inferior frontal cortex [Brodmann's area (BA) 44] was activated first (peak approximately 250 ms before the pinching); this activation was followed within 100-200 ms by activation in the left primary motor area (BA4) and 150-250 ms later in the right BA4. During imitation and observation, the sequence was otherwise similar, but it started from the left occipital cortex (BA19). Activation was always strongest during action imitation. Only the occipital activation was detected when the subject observed the experimenter reaching his hand without pinching. These results suggest that the left BA44 is the orchestrator of the human "mirror neuron system" and is strongly involved in action imitation. The mirror system matches action observation and execution and probably contributes to our understanding of actions made by others. [Abstract] [PDF] [Full Text]

Koski L, Iacoboni M, Dubeau MC, Woods RP, Mazziotta JC
Modulation of cortical activity during different imitative behaviors.
J Neurophysiol. 2003 Jan;89(1):460-71.
Imitation is a basic form of motor learning during development. We have a preference to imitate the actions of others as if looking in a mirror (specular imitation: i.e., when the actor moves the left hand, the imitator moves the right hand) rather than with the anatomically congruent hand (anatomic imitation: i.e., actor and imitator both moving the right hand). We hypothesized that this preference reflects changes in activity in previously described frontoparietal cortical areas involved in directly matching observed and executed actions (mirror neuron areas). We used functional magnetic resonance imaging to study brain activity in normal volunteers imitating left and right hand movements with their right hand. Bilateral inferior frontal and right posterior parietal cortex were more active during specular imitation compared with anatomic imitation and control motor tasks. Furthermore this same pattern of activity was also observed in the rostral part of the supplementary motor area (SMA-proper) of the right hemisphere. These findings suggest that the degree of involvement of frontoparietal mirror areas in imitation depends on the nature of the imitative behavior, ruling out a linguistic mediation of these areas in imitation. Moreover, activity in the SMA appears to be tightly coupled to frontoparietal mirror areas when subjects copy the actions of others. [Abstract] [PDF] [Full Text]

Ferrari PF, Rozzi S, Fogassi L
Mirror neurons responding to observation of actions made with tools in monkey ventral premotor cortex.
J Cogn Neurosci. 2005 Feb;17(2):212-26.
In the present study, we describe a new type of visuomotor neurons, named tool-responding mirror neurons, which are found in the lateral sector of monkey ventral premotor area F5. Tool-responding mirror neurons discharge when the monkey observes actions performed by an experimenter with a tool (a stick or a pair of pliers). This response is stronger than that obtained when the monkey observes a similar action made with a biological effector (the hand or the mouth). These neurons respond also when the monkey executes actions with both the hand and the mouth. The visual and the motor responses of each neuron are congruent in that they share the same general goal, that is, taking possession of an object and modifying its state. It is hypothesized that after a relatively long visual exposure to tool actions, a visual association between the hand and the tool is created, so that the tool becomes as a kind of prolongation of the hand. We propose that tool-responding mirror neurons enable the observing monkey to extend action-understanding capacity to actions that do not strictly correspond to its motor representations. Our findings support the notion that the motor cortex plays a crucial role in understanding action goals. [Abstract]

Järveläinen J, Schürmann M, Hari R
Activation of the human primary motor cortex during observation of tool use.
Neuroimage. 2004 Sep;23(1):187-92.
Tool use is a characteristic human trait, requiring motor skills that are largely learned by imitation. A neural system that supports imitation and action understanding by directly matching observed actions and their motor counterparts has been found in the human premotor and motor cortices. To test whether this "mirror-neuron system" (MNS) would be activated by observation of tool use, we recorded neuromagnetic oscillatory activity from the primary motor cortex of 10 healthy subjects while they observed the experimenter to use chopsticks in a goal-directed and non-goal-directed manner. The left and right median nerves were stimulated alternatingly, and the poststimulus rebounds of the approximately 20-Hz motor-cortex rhythms were quantified. Compared with the rest condition, the level of the approximately 20-Hz rhythm was suppressed during observation of both types of tool use, indicating activation of the primary motor cortex. The suppression was on average 15-17% stronger during observation of goal-directed than non-goal-directed tool use, and this difference correlated positively with the frequency of subjects' chopstick use during the last year. These results support the view that the motor-cortex activation is related to the observer's ability to understand and imitate motor acts. [Abstract]

Gallese V, Fadiga L, Fogassi L, Rizzolatti G
Action recognition in the premotor cortex.
Brain. 1996 Apr;119 ( Pt 2)593-609.
We recorded electrical activity from 532 neurons in the rostral part of inferior area 6 (area F5) of two macaque monkeys. Previous data had shown that neurons of this area discharge during goal-directed hand and mouth movements. We describe here the properties of a newly discovered set of F5 neurons ("mirror neurons', n = 92) all of which became active both when the monkey performed a given action and when it observed a similar action performed by the experimenter. Mirror neurons, in order to be visually triggered, required an interaction between the agent of the action and the object of it. The sight of the agent alone or of the object alone (three-dimensional objects, food) were ineffective. Hand and the mouth were by far the most effective agents. The actions most represented among those activating mirror neurons were grasping, manipulating and placing. In most mirror neurons (92%) there was a clear relation between the visual action they responded to and the motor response they coded. In approximately 30% of mirror neurons the congruence was very strict and the effective observed and executed actions corresponded both in terms of general action (e.g. grasping) and in terms of the way in which that action was executed (e.g. precision grip). We conclude by proposing that mirror neurons form a system for matching observation and execution of motor actions. We discuss the possible role of this system in action recognition and, given the proposed homology between F5 and human Brocca's region, we posit that a matching system, similar to that of mirror neurons exists in humans and could be involved in recognition of actions as well as phonetic gestures. [Abstract]

Rizzolatti G, Fadiga L, Gallese V, Fogassi L
Premotor cortex and the recognition of motor actions.
Brain Res Cogn Brain Res. 1996 Mar;3(2):131-41.
In area F5 of the monkey premotor cortex there are neurons that discharge both when the monkey performs an action and when he observes a similar action made by another monkey or by the experimenter. We report here some of the properties of these 'mirror' neurons and we propose that their activity 'represents' the observed action. We posit, then, that this motor representation is at the basis of the understanding of motor events. Finally, on the basis of some recent data showing that, in man, the observation of motor actions activate the posterior part of inferior frontal gyrus, we suggest that the development of the lateral verbal communication system in man derives from a more ancient communication system based on recognition of hand and face gestures. [Abstract]

Wohlschläger A, Bekkering H
Is human imitation based on a mirror-neurone system? Some behavioural evidence.
Exp Brain Res. 2002 Apr;143(3):335-41.
Recently, a population of neurones was discovered in the monkey's ( Macaca nemestrina) ventrolateral part of the pre-motor cortex (area F5). It is specialised for recognising object-oriented actions, regardless of whether these actions are performed or observed by the monkey. The latter observation led to the term mirror-neurones, and because these cells respond to both observed and executed actions, it seems likely that neurones of that type became co-opted during hominid evolution to serve the imitative behaviours that are so prevalent in our species. There is recent physiological evidence that Broca's area, the human ( Homo sapiens) homologue of monkey's area F5, is involved in the imitation of finger movements. However, concluding that human imitation is based on a mirror-neurone system is premature, because: (1) imitation in monkeys does not reach the same level as in humans or apes and (2) monkeys' mirror-neurones are specialised for object-oriented actions. This specialisation has not yet been demonstrated in adult humans. We investigated the role of objects in human imitation behaviour in a response time experiment. Subjects had to imitate downward movements of an index finger. In one condition, the observed finger touched one of two dots either ipsi- or contralaterally. In the other condition, the very same movements had to be imitated. However, there were no dots on the table. The presence of dots had a decisive influence on error patterns and on response times, but did not influence the movement proper. Dots specifically reduced the onset latency of ipsilateral finger movements and they specifically increased the use of the wrong finger, when contralateral movements were required. In general, results showed that objects also drive human imitation behaviour. Hence, it is very likely that imitation emerged from the mirror-neurone system of the common ancestor of monkeys and humans. [Abstract]

Keysers C, Kohler E, Umiltà MA, Nanetti L, Fogassi L, Gallese V
Audiovisual mirror neurons and action recognition.
Exp Brain Res. 2003 Dec;153(4):628-36.
Many object-related actions can be recognized both by their sound and by their vision. Here we describe a population of neurons in the ventral premotor cortex of the monkey that discharge both when the animal performs a specific action and when it hears or sees the same action performed by another individual. These 'audiovisual mirror neurons' therefore represent actions independently of whether these actions are performed, heard or seen. The magnitude of auditory and visual responses did not differ significantly in half the neurons. A neurometric analysis revealed that based on the response of these neurons, two actions could be discriminated with 97% accuracy. [Abstract] [PDF]

Kohler E, Keysers C, Umiltà MA, Fogassi L, Gallese V, Rizzolatti G
Hearing sounds, understanding actions: action representation in mirror neurons.
Science. 2002 Aug 2;297(5582):846-8.
Many object-related actions can be recognized by their sound. We found neurons in monkey premotor cortex that discharge when the animal performs a specific action and when it hears the related sound. Most of the neurons also discharge when the monkey observes the same action. These audiovisual mirror neurons code actions independently of whether these actions are performed, heard, or seen. This discovery in the monkey homolog of Broca's area might shed light on the origin of language: audiovisual mirror neurons code abstract contents-the meaning of actions-and have the auditory access typical of human language to these contents. [Abstract] [PDF]

Westermann G, Reck Miranda E
A new model of sensorimotor coupling in the development of speech.
Brain Lang. 2004 May;89(2):393-400.
We present a computational model that learns a coupling between motor parameters and their sensory consequences in vocal production during a babbling phase. Based on the coupling, preferred motor parameters and prototypically perceived sounds develop concurrently. Exposure to an ambient language modifies perception to coincide with the sounds from the language. The model develops motor mirror neurons that are active when an external sound is perceived. An extension to visual mirror neurons for oral gestures is suggested. [Abstract] [PDF]

Möttönen R, Järveläinen J, Sams M, Hari R
Viewing speech modulates activity in the left SI mouth cortex.
Neuroimage. 2005 Feb 1;24(3):731-7.
The ability to internally simulate other persons' actions is important for social interaction. In monkeys, neurons in the premotor cortex are activated both when the monkey performs mouth or hand actions and when it views or listens to actions made by others. Neuronal circuits with similar "mirror-neuron" properties probably exist in the human Broca's area and primary motor cortex. Viewing other person's hand actions also modulates activity in the primary somatosensory cortex SI, suggesting that the SI cortex is related to the human mirror-neuron system. To study the selectivity of the SI activation during action viewing, we stimulated the lower lip (with tactile pulses) and the median nerves (with electric pulses) in eight subjects to activate their SI mouth and hand cortices while the subjects either rested, listened to other person's speech, viewed her articulatory gestures, or executed mouth movements. The 55-ms SI responses to lip stimuli were enhanced by 16% (P<0.01) in the left hemisphere during speech viewing whereas listening to speech did not modulate these responses. The 35-ms responses to median-nerve stimulation remained stable during speech viewing and listening. Own mouth movements suppressed responses to lip stimuli bilaterally by 74% (P<0.001), without any effect on responses to median-nerve stimuli. Our findings show that viewing another person's articulatory gestures activates the left SI cortex in a somatotopic manner. The results provide further evidence for the view that SI is involved in "mirroring" of other persons' actions. [Abstract]

Ferrari PF, Gallese V, Rizzolatti G, Fogassi L
Mirror neurons responding to the observation of ingestive and communicative mouth actions in the monkey ventral premotor cortex.
Eur J Neurosci. 2003 Apr;17(8):1703-14.
In the ventral premotor cortex (area F5) of the monkey there are neurons that discharge both when the monkey performs specific motor actions and when it observes another individual performing a similar action (mirror neurons). Previous studies on mirror neurons concerned hand actions. Here, we describe the mirror responses of F5 neurons that motorically code mouth actions. The results showed that about one-third of mouth motor neurons also discharge when the monkey observes another individual performing mouth actions. The majority of these 'mouth mirror neurons' become active during the execution and observation of mouth actions related to ingestive functions such as grasping, sucking or breaking food. Another population of mouth mirror neurons also discharges during the execution of ingestive actions, but the most effective visual stimuli in triggering them are communicative mouth gestures (e.g. lip smacking). Some also fire when the monkey makes communicative gestures. These findings extend the notion of mirror system from hand to mouth action and suggest that area F5, the area considered to be the homologue of human Broca's area, is also involved in communicative functions. [Abstract]

Tettamanti M, Buccino G, Saccuman MC, Gallese V, Danna M, Scifo P, Fazio F, Rizzolatti G, Cappa SF, Perani D
Listening to action-related sentences activates fronto-parietal motor circuits.
J Cogn Neurosci. 2005 Feb;17(2):273-81.
Observing actions made by others activates the cortical circuits responsible for the planning and execution of those same actions. This observation-execution matching system (mirror-neuron system) is thought to play an important role in the understanding of actions made by others. In an fMRI experiment, we tested whether this system also becomes active during the processing of action-related sentences. Participants listened to sentences describing actions performed with the mouth, the hand, or the leg. Abstract sentences of comparable syntactic structure were used as control stimuli. The results showed that listening to action-related sentences activates a left fronto-parieto-temporal network that includes the pars opercularis of the inferior frontal gyrus (Broca's area), those sectors of the premotor cortex where the actions described are motorically coded, as well as the inferior parietal lobule, the intraparietal sulcus, and the posterior middle temporal gyrus. These data provide the first direct evidence that listening to sentences that describe actions engages the visuomotor circuits which subserve action execution and observation. [Abstract]

Papathanasiou I, Filipovi? SR, Whurr R, Rothwell JC, Jahanshahi M
Changes in corticospinal motor excitability induced by non-motor linguistic tasks.
Exp Brain Res. 2004 Jan;154(2):218-25.
The excitability of the corticospinal motor pathways to transcranial magnetic stimulation (TMS) can be differentially modulated by a variety of motor tasks. However, there is emerging evidence that linguistic tasks may alter excitability of the corticospinal motor pathways also. In this study we evaluated the effect of several movement-free, low-level linguistic processes involved in reading and writing on the excitability of the bilateral corticospinal motor pathways in a group of right-handed subjects. The study included two series of tasks, visual searching/matching and imaginal writing/drawing. The tasks were designed to roughly correspond with elemental aspects of the reading and writing, grapheme recognition and grapheme generation, respectively. Each task series included separate blocks with different task targets: letters, digits, semantically easy-to-code (i.e. geometric) shapes, and semantically hard-to-code shapes, as well as control blocks with no task. During task performance, TMS was delivered randomly over the hand area of either the left or right motor cortex and the modulation of the excitability of the corticospinal motor pathways was measured bilaterally through changes of the size of the motor-evoked potential (MEP) induced in the relaxed right and left first dorsal interosseous (FDI) muscles. We found that the size of the MEP in hand muscles increased during visual searching/matching tasks, particularly when targets were letters or geometric shapes, and the increase was significant for the dominant hand (left hemisphere) only. No such consistent effects were seen across subjects during imaginal tasks. This study provides evidence that even the performance of certain low-level linguistic tasks can modulate the excitability of the corticospinal motor pathways, particularly those originating from the left (dominant) hemisphere, despite the absence of overt motor activity. Moreover, in the light of the recently increased awareness of the role of "mirror neurons" in perception, the results suggest that activation of motor circuits used in generation of the written output may be an essential part of the perception of the written material as well. Understanding the patterns of task-dependent changes in excitability of the corticospinal motor pathways will provide insights into the organisation of central nervous system functional networks involved in linguistic processes, and may also be useful for future development of novel approaches to rehabilitation therapy of linguistic and motor functions. [Abstract]

Stein JF
Why did language develop?
Int J Pediatr Otorhinolaryngol. 2003 Dec;67 Suppl 1S131-5.
Language developed for communication, to facilitate learning the use of tools and weapons, to plan hunting and defence, to develop a "theory of mind" and the tools of thought, and to attract and keep a mate. The adaptations required took place over many millions of years. The first important one was left-sided specialisation of the neural apparatus controlling involuntary emotional vocalisations that began more than 200 million years ago. The next was the development in primates of "mirror neurones" in the pre-motor cortex some 45 million years ago. These enabled the imitation and voluntary control of previously involuntary manual gestures and vocalisations. The third important adaptation was the descent of the larynx, 100,000 years ago, which greatly increased the phonological range of vocalisations that could be made. Thus, language did not develop all at once as suggested by Chomsky, but evolved gradually building upon adaptations originally meeting quite different needs. [Abstract]

Corballis MC
From mouth to hand: gesture, speech, and the evolution of right-handedness.
Behav Brain Sci. 2003 Apr;26(2):199-208; discussion 208-60.
The strong predominance of right-handedness appears to be a uniquely human characteristic, whereas the left-cerebral dominance for vocalization occurs in many species, including frogs, birds, and mammals. Right-handedness may have arisen because of an association between manual gestures and vocalization in the evolution of language. I argue that language evolved from manual gestures, gradually incorporating vocal elements. The transition may be traced through changes in the function of Broca's area. Its homologue in monkeys has nothing to do with vocal control, but contains the so-called "mirror neurons," the code for both the production of manual reaching movements and the perception of the same movements performed by others. This system is bilateral in monkeys, but predominantly left-hemispheric in humans, and in humans is involved with vocalization as well as manual actions. There is evidence that Broca's area is enlarged on the left side in Homo habilis, suggesting that a link between gesture and vocalization may go back at least two million years, although other evidence suggests that speech may not have become fully autonomous until Homo sapiens appeared some 170,000 years ago, or perhaps even later. The removal of manual gesture as a necessary component of language may explain the rapid advance of technology, allowing late migrations of Homo sapiens from Africa to replace all other hominids in other parts of the world, including the Neanderthals in Europe and Homo erectus in Asia. Nevertheless, the long association of vocalization with manual gesture left us a legacy of right-handedness. [Abstract] [PDF]

Arbib MA
Rana computatrix to human language: towards a computational neuroethology of language evolution.
Philos Transact A Math Phys Eng Sci. 2003 Oct 15;361(1811):2345-79.
Walter's Machina speculatrix inspired the name Rana computatrix for a family of models of visuomotor coordination in the frog, which contributed to the development of computational neuroethology. We offer here an 'evolutionary' perspective on models in the same tradition for rat, monkey and human. For rat, we show how the frog-like taxon affordance model provides a basis for the spatial navigation mechanisms that involve the hippocampus and other brain regions. For monkey, we recall two models of neural mechanisms for visuomotor coordination. The first, for saccades, shows how interactions between the parietal and frontal cortex augment superior colliculus seen as the homologue of frog tectum. The second, for grasping, continues the theme of parieto-frontal interactions, linking parietal affordances to motor schemas in premotor cortex. It further emphasizes the mirror system for grasping, in which neurons are active both when the monkey executes a specific grasp and when it observes a similar grasp executed by others. The model of human-brain mechanisms is based on the mirror-system hypothesis of the evolution of the language-ready brain, which sees the human Broca's area as an evolved extension of the mirror system for grasping. [Abstract] [Full Text]

Williams JH, Whiten A, Suddendorf T, Perrett DI
Imitation, mirror neurons and autism.
Neurosci Biobehav Rev. 2001 Jun;25(4):287-95.
Various deficits in the cognitive functioning of people with autism have been documented in recent years but these provide only partial explanations for the condition. We focus instead on an imitative disturbance involving difficulties both in copying actions and in inhibiting more stereotyped mimicking, such as echolalia. A candidate for the neural basis of this disturbance may be found in a recently discovered class of neurons in frontal cortex, 'mirror neurons' (MNs). These neurons show activity in relation both to specific actions performed by self and matching actions performed by others, providing a potential bridge between minds. MN systems exist in primates without imitative and 'theory of mind' abilities and we suggest that in order for them to have become utilized to perform social cognitive functions, sophisticated cortical neuronal systems have evolved in which MNs function as key elements. Early developmental failures of MN systems are likely to result in a consequent cascade of developmental impairments characterised by the clinical syndrome of autism. [Abstract] [PDF]

Williams JH, Massaro DW, Peel NJ, Bosseler A, Suddendorf T
Visual-auditory integration during speech imitation in autism.
Res Dev Disabil. 2004 Nov-Dec;25(6):559-75.
Children with autistic spectrum disorder (ASD) may have poor audio-visual integration, possibly reflecting dysfunctional 'mirror neuron' systems which have been hypothesised to be at the core of the condition. In the present study, a computer program, utilizing speech synthesizer software and a 'virtual' head (Baldi), delivered speech stimuli for identification in auditory, visual or bimodal conditions. Children with ASD were poorer than controls at recognizing stimuli in the unimodal conditions, but once performance on this measure was controlled for, no group difference was found in the bimodal condition. A group of participants with ASD were also trained to develop their speech-reading ability. Training improved visual accuracy and this also improved the children's ability to utilize visual information in their processing of speech. Overall results were compared to predictions from mathematical models based on integration and non-integration, and were most consistent with the integration model. We conclude that, whilst they are less accurate in recognizing stimuli in the unimodal condition, children with ASD show normal integration of visual and auditory speech stimuli. Given that training in recognition of visual speech was effective, children with ASD may benefit from multi-modal approaches in imitative therapy and language training. [Abstract]

Villalobos ME, Mizuno A, Dahl BC, Kemmotsu N, Müller RA
Reduced functional connectivity between V1 and inferior frontal cortex associated with visuomotor performance in autism.
Neuroimage. 2005 Apr 15;25(3):916-25.
Some recent evidence has suggested abnormalities of the dorsal stream and possibly the mirror neuron system in autism, which may be responsible for impairments of joint attention, imitation, and secondarily for language delays. The current study investigates functional connectivity along the dorsal stream in autism, examining interregional blood oxygenation level dependent (BOLD) signal cross-correlation during visuomotor coordination. Eight high-functioning autistic men and eight handedness and age-matched controls were included. Visually prompted button presses were performed with the preferred hand. For each subject, functional connectivity was computed in terms of BOLD signal correlation with the mean time series in bilateral visual area 17. Our hypothesis of reduced dorsal stream connectivity in autism was only in part confirmed. Functional connectivity with superior parietal areas was not significantly reduced. However, the autism group showed significantly reduced connectivity with bilateral inferior frontal area 44, which is compatible with the hypothesis of mirror neuron defects in autism. More generally, our findings suggest that dorsal stream connectivity in autism may not be fully functional. [Abstract]

Fecteau S, Carmant L, Tremblay C, Robert M, Bouthillier A, Théoret H
A motor resonance mechanism in children? Evidence from subdural electrodes in a 36-month-old child.
Neuroreport. 2004 Dec 3;15(17):2625-7.
The presence of a neural mechanism matching execution and observation of actions in the adult human brain is well established. In children, however, description of a resonance motor mechanism is still preliminary. In the present study, we recorded electroencephalographic signals from a subdural 64-contact grid electrode in a 36-month-old child with epilepsy. Spectral analysis was performed on sequences where the child drew with her right hand, watched an experimenter drawing with his right hand or was at rest. Contact sites corresponding to sensorimotor areas were discovered where absolute power was decreased during both observation and execution of hand/arm actions. These data suggest the presence of a mirror neuron system early in the developing brain. [Abstract]

Fadiga L, Craighero L
Electrophysiology of action representation.
J Clin Neurophysiol. 2004 May-Jun;21(3):157-69.
We continuously act on objects, on other individuals, and on ourselves, and actions represent the only way we have to manifest our own desires and goals. In the last two decades, electrophysiological experiments have demonstrated that actions are stored in the brain according to a goal-related organization. The authors review a series of experimental data showing that this "vocabulary of motor schemata" could also be used for non-strictly motor purposes. In the first section, they present data from monkey experiments describing the functional properties of inferior premotor cortex and, in more detail, the properties of visuomotor neurons responding to objects and others' actions observation (mirror neurons). In the second section, human data are reviewed, with particular regard to electrophysiological experiments aiming to investigate how action representations are stored and addressed. The specific facilitatory effect of motor imagery, action/object observation, and speech listening on motor excitability shown by these experiments provides strong evidence that the motor system is constantly involved whenever the idea of an action is evoked. [Abstract] [PDF]

Muthukumaraswamy SD, Johnson BW
Primary motor cortex activation during action observation revealed by wavelet analysis of the EEG.
Clin Neurophysiol. 2004 Aug;115(8):1760-6.
OBJECTIVE: We characterised the spectral response of the EEG to median nerve stimulation using wavelet analysis, and compared the relative magnitudes of effect of several different action-observation conditions on the beta and mu 'rebound' rhythms. METHODS: EEG responses to median nerve stimulation were recorded from 8 normal adult subjects during baseline or action-observation conditions. Analysis was performed by convolution of the EEG with a family of wavelets. RESULTS: Decreased power in the mu and beta bands characterized the EEG following median nerve stimulation until 500 ms post-stimulus, followed by increased amplitudes ('rebound') of both rhythms. Execution of movement, observation of object-directed movement and observation of somatosensory stimulation all caused a decreased rebound of the beta rhythm whereas observation of aimless thumb movement did not. CONCLUSIONS: Wavelet analysis of the EEG extracted similar features reported in previous studies using bandpass filtering with respect to the activation state of the motor cortex during action observation. Further, our results show that observation of somatosensory stimulation alone is sufficient to cause significant modulation of motor cortex activity. SIGNIFICANCE: These results add further details as to what stimuli can activate the human mirror neuron system and the analytical techniques used may be useful for future studies of clinical populations such as autistic patients. [Abstract]

Muthukumaraswamy SD, Johnson BW, McNair NA
Mu rhythm modulation during observation of an object-directed grasp.
Brain Res Cogn Brain Res. 2004 Apr;19(2):195-201.
Recent electrophysiological studies have shown that the human electroencephalographic mu rhythm is suppressed during the observation of actions performed by other persons, an effect that may be functionally related to the behaviour of so-called "mirror neurons" observed in area F5 of nonhuman primates. Because mirror neuron activity has been reported to be functionally specific to object-oriented actions, the present study was designed to determine if the human mu rhythm also exhibits this property. EEG measurements were obtained from 12 normal subjects while they observed either a precision grip of a manipulandum or an empty grip using the same hand position. Our results showed that the magnitude of the mu rhythm was significantly lower for the object grip condition than for the empty grip condition. These data support the notion that the human mu rhythm indexes a brain system that is functionally comparable to the monkey mirror neuron system. We propose that nonobject-directed actions may result in representational schemas that are either different or less salient than motorically equivalent actions that are directed toward objects. [Abstract] [PDF]

Gangitano M, Mottaghy FM, Pascual-Leone A
Phase-specific modulation of cortical motor output during movement observation.
Neuroreport. 2001 May 25;12(7):1489-92.
The effects of different phases of an observed movement on the modulation of cortical motor output were studied by means of transcranial magnetic stimulation (TMS). A video-clip of a reaching-grasping action was shown and single TMS pulses were delivered during its passive observation. Times of cortical stimulation were related to the phases of the shown movement, locking them to the appearance of specific kinematic landmarks. The amplitude of the motor evoked potentials (MEPs) induced by TMS in the first dorsal interosseus (FDI) muscle was modulated by the amount of the observed finger aperture. The presence of such an effect is consistent with the notion of a mirror neuron system in premotor areas that couples action execution and action observation also in terms of temporal coding. [Abstract]

Miall RC
Connecting mirror neurons and forward models.
Neuroreport. 2003 Dec 2;14(17):2135-7.
Two recent developments in motor neuroscience are promising the extension of theoretical concepts from motor control towards cognitive processes, including human social interactions and understanding the intentions of others. The first of these is the discovery of what are now called mirror neurons, which code for both observed and executed actions. The second is the concept of internal models, and in particular recent proposals that forward and inverse models operate in paired modules. These two ideas will be briefly introduced, and a recent suggestion linking between the two processes of mirroring and modelling will be described which may underlie our abilities for imitating actions, for cooperation between two actors, and possibly for communication via gesture and language. [Abstract] [PDF]

Järveläinen J, Schürmann M, Avikainen S, Hari R
Stronger reactivity of the human primary motor cortex during observation of live rather than video motor acts.
Neuroreport. 2001 Nov 16;12(16):3493-5.
The monkey premotor cortex contains neurons that are activated both when the monkey performs motor acts and when he observes actions made by others. A similar mirror neuron system, involving several brain areas, has been found in humans. We recorded neuromagnetic oscillatory activity from the primary motor cortex of 10 healthy subjects when they observed live and videotaped finger movements. The left and right median nerves were stimulated alternatingly and the poststimulus level of the approximately 20 Hz rhythm was quantified. Compared with the rest condition, the approximately 20 Hz rhythm was dampened 15-19% more when the subjects observed live rather than videotaped hand movements, indicating stronger activation of the primary motor cortex. These results suggest that the human mirror neuron system differentiates natural and artificially presented movements. [Abstract]

Bodini B, Iacoboni M, Lenzi GL
Acute stroke effects on emotions: an interpretation through the mirror system.
Curr Opin Neurol. 2004 Feb;17(1):55-60.
PURPOSE OF REVIEW: The most recent reports on emotional consequences of stroke are hereby reviewed and analyzed. In particular the interpretation of some neurological presentations found in stroke patients, such as athymormia, dysprosody, emotional incontinence and emotional blunting is discussed. As current theories on mental functions do not provide satisfactory explanations for the above syndromes, a novel interpretative framework is proposed, based on neuropsychological experimental data on the 'mirror system'. RECENT FINDINGS: Recent findings support both the fundamental role of the mirror system in imitative processes as well as the relevance of imitation for the emotional part of human personality and behavior. SUMMARY: The mirror system appears to be of paramount relevance for empathy and social behavior. The model of analysis-by-synthesis is here discussed, together with neurological presentations resulting from stroke induced impairments of the mirror system. Speculations for further researches are also proposed. [Abstract] [PDF]

Pomeroy VM, Clark CA, Miller JS, Baron JC, Markus HS, Tallis RC
The Potential for Utilizing the "Mirror Neurone System" to Enhance Recovery of the Severely Affected Upper Limb Early after Stroke: A Review and Hypothesis.
Neurorehabil Neural Repair. 2005 Mar;19(1):4-13.
Recovery of upper limb movement control after stroke might be enhanced by repetitive goal-directed functional activities. Providing such activity is challenging in the presence of severe paresis. A possible new approach is based on the discovery of mirror neurons in the monkey cortical area F5, which are active both in observing and executing a movement. Indirect evidence for a comparable human "mirror neurone system" is provided by functional imaging. The primary motor cortex, the premotor cortex, other brain areas, and muscles appropriate for the action being observed are probably activated in healthy volunteers observing another's movement. These findings raise the hypothesis that observation of another's movement might train the movement execution system of stroke patients who have severe paresis to bring them to the point at which they could actively participate in rehabilitation consisting of goal-directed activities. The point of providing an observation therapy would be to facilitate the voluntary production of movement; therefore, the condition of interest would be observation with intent to imitate. However, there is as yet insufficient evidence to enable the testing of this hypothesis in stroke patients. Studies in normal subjects are needed to determine which brain sites are activated in response to observation with intent to imitate. Studies in stroke subjects are needed to determine how activation is affected after damage to different brain areas. The information from such studies should aid identification of those stroke patients who might be most likely to benefit from observation to imitate and therefore guide phase I clinical studies. [Abstract]