188 TINS Vol. 21, No. 5, 1998 Copyright © 1998, Elsevier Science Ltd. All rights reserved. 0166 - 2236/98/$19.00 PII: S0166-2236(98)01260-058 Schacher, S., Castellucci, V.F. and Kandel, E.R. (1988) Science240, 1667–1669 59 Dash, P.K., Moore, A.N. and Dixon, C.E. (1995) J. Neurosci. 15,2030–2039 60 Schulman, H. (1995) Curr. Opin. Neurobiol. 5, 375–381 61 Moore, A.N., Waxham, M.N. and Dash, P.K. (1996) J. Biol.Chem. 271, 14214–14220 62 Blendy, J.A. et al. (1995) Brain Res. 681, 8–14 63 Deisseroth, K., Bito, H. and Tsien, R.W. (1996) Neuron 16,89–101 64 Das, S. et al. (1997) Synapse 25, 227–233 65 Seidenbecher, T., Reymann, K.G. and Balschun, D. (1997)Proc. Natl. Acad. Sci. U. S. A. 94, 1494–1499 66 Gustafsson, B. and Wigström, H. (1990) Prog. Brain Res. 83,223–232 67 Morris, R.G.M. and Frey, U. (1997) Philos. Trans. R. Soc. London352, 1489–1503 68 Nadel, L. and Moscovitch, M. (1997) Curr. Opin. Neurobiol. 7,217–227 69 Stäubli, U. and Chun, D. (1996) J. Neurosci. 16, 853–860 70 Clark, K.A. and Collingridge, G.L. (1996) J. Physiol. 490,455–462 U. Frey and R.G.M. Morris – Late LTPV I E W P O I N T Language within our graspGiacomo Rizzolatti and Michael A. ArbibIn monkeys,the rostral part of ventral premotor cortex (area F5) contains neurons that discharge,both when the monkey grasps or manipulates objects and when it observes the experimentermaking similar actions.These neurons (mirror neurons) appear to represent a system that matchesobserved events to similar, internally generated actions, and in this way forms a link between theobserver and the actor. Transcranial magnetic stimulation and positron emission tomography(PET) experiments suggest that a mirror system for gesture recognition also exists in humans andincludes Broca’s area. We propose here that such an observation/execution matching systemprovides a necessary bridge from ‘doing’ to ‘communicating’,as the link between actor and observerbecomes a link between the sender and the receiver of each message.Trends Neurosci. (1998) 21, 188–194‘In all communication, sender and receiver mustbe bound by a common understanding aboutwhat counts; what counts for the sender mustcount for the receiver, else communication doesnot occur. Moreover the processes of productionand perception must somehow be linked; theirrepresentation must, at some point, be the same.’ WHAT IS SAID HERE by Alvin Liberman1forspeech where individuals have an explicit intentto communicate, must apply also for ‘communi-cations’ in which such an overt intention is absent. Weunderstand when one individual is attacking anotheror when someone is peacefully eating an apple. Howdo we do it? What is shared by the (involuntary)sender and by the receiver? Is this mechanism the pre-cursor of willed communications? The present reviewaddresses these questions.The mirror systemNeurons located in the rostral part of monkey inferior area 6 (area F5) discharge during active move-ments of the hand or mouth, or both2–4. Some yearsago we found that in most F5 neurons, the dischargecorrelates with an action, rather than with the indi-vidual movements that form it3. Accordingly, we clas-sified F5 neurons into various categories correspond-ing to the action associated with their discharge. Themost common are: ‘grasping with the hand’ neurons,‘holding’ neurons and ‘tearing’ neurons3,5. Furtherstudy revealed something unexpected: a class of F5neurons that discharge not only when the monkeygrasped or manipulated the objects, but also when themonkey observed the experimenter making a similargesture6–8. We called the neurons endowed with thisproperty ‘mirror neurons’ (Fig. 1).The response properties of mirror neurons to visualstimuli can be summarized as follows: mirror neuronsdo not discharge in response to object presentation; inorder to be triggered they require a specific observedaction. The majority of them respond selectivelywhen the monkey observes one type of action (such asgrasping). Some are highly specific, coding not onlythe action aim, but also how that action is executed.They fire, for example, during observation of graspingmovements, but only when the object is grasped withthe index finger and the thumb.All mirror neurons show visual generalization: theydischarge when the agent of the observed action (typi-cally a hand) is far away from or close to the monkey.A few neurons respond even when the object isgrasped by the mouth. The actions most representedare: grasp, manipulate, tear, and put an object on aplate. Mirror neurons also have motor properties thatare indistinguishable from those of F5 neurons that donot respond to action observation. In this review, theywill be referred to collectively and regardless of theirother properties, as ‘canonical neurons’. Typically,mirror neurons show congruence between theobserved and executed action. This congruence can beextremely strict, that is, the effective motor action (forexample, precision grip) corresponds with the actionthat, when seen, triggers the neuron (that is, precisiongrip). For other neurons the congruence is broader:the motor requirements (for example, precision grip)are usually stricter than the visual ones (for example,any type of hand grasping). An example of a highlycongruent mirror neuron is shown in Fig. 2. What isGiacomo Rizzolattiis at the Istituto diFisiologia Umana,Università diParma, ViaGramsci 14,43100 Parma,Italy, andMichael A. Arbibis at the USCBrain Project,University ofSouthernCalifornia, Los Angeles, CA 90089-2520,USA.TINS Vol. 21, No. 5, 1998 189the function of mirror neurons? The proposal thatwe7,8and others9have advanced is that their activity‘represents’ actions. This representation can be usedfor imitating actions and for understanding them. By‘understanding’ we mean the capacity that individualshave to recognize that another individual is perform-ing an action, to differentiate the observed actionfrom other actions, and to use this information to actappropriately. According to this view, mirror neuronsrepresent the link between sender and receiver thatLiberman postulated in his motor theory of speechperception as the necessary prerequisite for any typeof communication1,10,11.What is