ANRV364-PS60-25 ARI 24 November 2008 18:59 Imitation, Empathy, and Mirror Neurons Marco Iacoboni Ahmanson-Lovelace Brain Mapping Center, Department of Psychiatry and Biobehavioral Sciences, Semel Institute for Neuroscience and Social Behavior, Brain Research Institute, David Geffen School of Medicine at UCLA, Los Angeles, California 90095; email: [email protected] Annu. Rev. Psychol. 2009. 60:653–70 Key Words First published online as a Review in Advance on social cognition, theory of mind, mirror neuron system, embodiment September 15, 2008 The Annual Review of Psychology is online at Abstract psych.annualreviews.org There is a convergence between cognitive models of imitation, con- This article’s doi: structs derived from social psychology studies on mimicry and empa- by HARVARD UNIVERSITY on 03/06/09. For personal use only. 10.1146/annurev.psych.60.110707.163604 thy, and recent empirical findings from the neurosciences. The ideomo- Copyright c 2009 by Annual Reviews. tor framework of human actions assumes a common representational All rights reserved format for action and perception that facilitates imitation. Further- Annu. Rev. Psychol. 2009.60:653-670. Downloaded from arjournals.annualreviews.org 0066-4308/09/0110-0653$20.00 more, the associative sequence learning model of imitation proposes that experience-based Hebbian learning forms links between sensory processing of the actions of others and motor plans. Social psychol- ogy studies have demonstrated that imitation and mimicry are per- vasive, automatic, and facilitate empathy. Neuroscience investigations have demonstrated physiological mechanisms of mirroring at single-cell and neural-system levels that support the cognitive and social psychol- ogy constructs. Why were these neural mechanisms selected, and what is their adaptive advantage? Neural mirroring solves the “problem of other minds” (how we can access and understand the minds of others) and makes intersubjectivity possible, thus facilitating social behavior. 653 ANRV364-PS60-25 ARI 24 November 2008 18:59 Among cognitive models of imitation, the Contents ideomotor model and the associative sequence learning model seem to map well onto neu- INTRODUCTION .................. 654 rophysiological mechanisms of imitation. The COGNITIVE MECHANISMS ideomotor model assumes a common rep- OF IMITATION .................. 654 resentational format for action and percep- The Ideomotor Framework tion, whereas the associative sequence learning of Imitation..................... 654 model puts at center stage Hebbian learning as Associative Sequence Learning ..... 656 a fundamental mechanism linking sensory rep- IMITATION AND EMPATHY resentations of the actions of others to motor IN SOCIAL BEHAVIOR .......... 657 plans. Furthermore, social psychology studies Pervasiveness and Automaticity have documented the automaticity of imitation of Human Imitation............. 657 and mimicry in humans, a feature that also maps NEURAL MECHANISMS well onto some recently disclosed neurophysi- OF IMITATION .................. 659 ological bases of imitation. Neural Precursors This review discusses cognitive models, so- in Nonhuman Primates ......... 659 cial psychology constructs, and neural mech- Macaque Mirror Neurons anisms of imitation under the hypothesis that and Imitation in Monkeys ....... 662 these mechanisms were selected because they Human Brain Mechanisms offer the adaptive advantage of enabling the un- of Mirroring .................... 663 derstanding of the feelings and mental states of Neural Mirroring and Psychological others, a cornerstone of social behavior. Theories of Imitation ........... 665 WHY NEURAL MIRRORING AND IMITATION? ............... 666 COGNITIVE MECHANISMS OF IMITATION The Ideomotor Framework INTRODUCTION of Imitation Although mimicry is a pervasive phenomenon Theories of action can be divided into two in the animal kingdom, imitation certainly main frameworks. The most dominant frame- achieves its highest form in humans. Past work may be called the sensory-motor frame- authors—for instance, de Montaigne (1575), work of action. It assumes that actions are ini- by HARVARD UNIVERSITY on 03/06/09. For personal use only. Adam Smith (1759), Poe (1982), Nietzsche tiated in response to external stimuli. In this (1881), and Wittgenstein (1980)—have often framework, perception and action have inde- associated imitation with the ability to em- pendent representational formats. Stimuli must Annu. Rev. Psychol. 2009.60:653-670. Downloaded from arjournals.annualreviews.org pathize and understand other minds. The evo- be translated into motor responses by stimulus- lutionary, functional, and neural mechanisms response mapping mechanisms. This frame- linking imitation to empathy, however, have work has generated a large literature and el- been unclear for many years. Recently, there has egant experimental paradigms, as for instance Hebbian learning: been a convergence between cognitive mod- the work on stimulus-response compatibility associative learning is els of imitation, social psychology accounts of (Hommel & Prinz 1997, Proctor & Reeve implemented by simultaneous its pervasiveness and its functional links with 1990). Stimulus-response translational mecha- activation of cells that empathy and liking, and the neuroscience dis- nisms, however, do not easily account for the would lead to coveries of neural mechanisms of imitation similarity between the observed action and the increased synaptic and empathy. This convergence creates a solid action performed by the imitator that is re- strength between the framework in which theory and empirical data quired by imitation. Indeed, one of the main cells reinforce each other. problems of imitation often discussed in the 654 Iacoboni ANRV364-PS60-25 ARI 24 November 2008 18:59 literature inspired by sensory-motor models tor plan to lift the same finger. Brass and col- is the so-called correspondence problem (Ne- leagues tested this hypothesis in elegantly sim- haniv & Dautenhahn 2002). This problem ple experiments (Brass et al. 2000, 2001). Sub- can be summarized with the question: how is jects were shown two movements of the index the sensory input from somebody else’s action finger from the same starting position. In half transformed into a matching motor output by of the trials the finger would move upward, the imitator? and in the other half it would move downward. For the ideomotor framework of action, the Subjects were instructed to respond as fast as correspondence problem of imitation is not a possible using their own index finger. Within problem at all. Indeed, the ideomotor frame- each block of trials, subjects were instructed to work assumes a common representational for- use always the same motor response, either an mat for perception and action, an assump- upward or a downward movement. Thus, al- tion that makes translational processes between though perceptually subjects were seeing both stimuli and responses rather unnecessary. The upward and downward movements, motorically roots of the ideomotor framework were estab- they were only executing one of the two move- lished by the work of Hermann Martin Lotze ments. Given that response selection was not (Prinz 2005) and William James (1890). The required, the identity of the stimulus was com- starting point of actions, for Lotze and James, pletely irrelevant for the initiation of the motor is not a response to a sensory stimulation, but response. Here, the sensory-motor framework rather the representation of the goal that the would predict similar reaction times for re- agent intends to achieve. When an intention sponses that were identical to the stimulus (e.g., is unchallenged by a conflicting one, it acti- upward motor response for a stimulus showing vates the representation of the intended goal an upward finger movement) and for responses and the motor plan necessary to achieve it. The that were different from the stimulus (e.g., up- coactivation of the intended goal and the mo- ward motor response for a stimulus showing a tor plan required to achieve it—according to downward finger movement). In contrast, the the ideomotor framework—is the result of our ideomotor framework would predict faster re- experience. We have learned the effects of our action times for motor responses identical to own actions, and we expect certain effects when the stimulus compared to motor responses dif- we perform certain acts. This previous learning ferent from the stimulus. The results demon- makes it possible that just thinking about the strated a large chronometric advantage for re- intended goal automatically activates the rep- sponses identical to the stimuli, in line with the resentation of the action necessary to obtain it. predictions of the ideomotor framework (Brass by HARVARD UNIVERSITY on 03/06/09. For personal use only. Thus, when I think about rebooting my com- et al. 2000, 2001). puter, I automatically activate the representa- The ideomotor framework also predicts that tion of the finger movement necessary to press goals have higher priority than movements in Annu. Rev. Psychol. 2009.60:653-670. Downloaded from arjournals.annualreviews.org the appropriate key. imitation. Imitation experiments in children The ideomotor framework naturally ac- have confirmed this prediction. In one of these counts for imitation. According to this frame- experiments (Bekkering et al. 2000), children work, when I see somebody else’s actions and and experimenters were sitting on the opposite their consequences, I activate the representa- sides