When we watch a traffic light change fromred to green, we can predict the behavior of adriver waiting in his car in front of it. Doesthis prediction involve a simulation of the dri-ver’s cognitive processes used to plan acceler-ating? Or does one use inferential anddeductive processes that do not involve simu-lation to come to the conclusion that he willaccelerate? To find out whether the neuralprocesses involved in preparing our ownactions are also used to predict the futureactions of others, Ramnani and Miall devel-oped a clever associative visuomotortask, in which subjects learned to asso-ciate arbitrary visual instruction cueswith finger movements (Fig. 1). Duringthe actual experiment, they were led tobelieve that another participant whohad undergone training together withthem was performing the task inanother room. The color of the instruc-tion cue specified who should performthe action: the participant beingscanned (first person), the trainingpartner in the other room (third per-son) or a computer (non-biologicalagent). On some trials, the shape of theinstruction cue specified the fingermovement that was to be performed, sothat a subsequent trigger cue only indi-cated when the action should be initi-ated (specific instruction). In this case,the action could be planned in advance.On other trials, the shape of theinstruction cue did not indicate the fin-ger movement, which was specifiedonly by the trigger cue (unspecificinstruction). In this case, the actioncould not be planned in advance.

The comparison between specificversus non-specific instruction cues

for the first-person condition showed dif-ferential activity in dorsal premotor cortex(PMd). This finding is in line with previ-ous studies showing that PMd is activatedwhen subjects plan to perform arbitrarystimulus-response associations4. The com-parison between third person and com-puter across the two instruction typesreveals the main effect of intentionalstance—anticipating the action of ahuman actor versus a non-biologicalagent5. As expected from prior results, this

N E W S A N D V I E W S

How can we read the intentions of other peo-ple and thereby predict their future actions?The cognitive basis of this ability, known as‘having a theory of mind’ (ToM), is currentlythe subject of vigorous debate. Do we attrib-ute mental states to others by simulatingtheir cognitive processes or do we use infer-ential and deductive processes that do notrequire simulation1? In this issue, Ramnaniand Miall2 make a significant contribution tothe debate between ‘simulation theorists’ and‘theory theorists’ by investigating the neuralprocesses involved in the prediction of a verysimple action made by another person.

Their results show that areas within thehuman action control system are indeedactivated when predicting another’s actions.However, they are not the areas activatedwhen we prepare to make the same actionourselves. Furthermore, predicting another’saction also leads to activation in brain areasthat are typically engaged in tasks thatinvolve complex mental state attributions3.These findings are interesting for two rea-sons. First, they suggest that a simple form ofsimulation cannot be the only mechanisminvolved in predicting actions and under-standing intentions of others. Second, theyprovide evidence that even representing theaction that someone else performs in a sim-ple task elicits processes involved in ToM .

Natalie Sebanz is at the Max Planck Institute for

Psychological Research, Amalienstr. 33, 80799

Munich, Germany. Chris Frith is at the Wellcome

Department of Imaging Neuroscience, Institute of

Neurology, University College London, 12 Queen

Square, London WC1N 3BG, UK.

e-mail: sebanz@psy.mpg.de;

cfrith@fil.ion.ucl.ac.uk

Beyond simulation? Neural mechanisms forpredicting the actions of othersNatalie Sebanz & Chris Frith

Our ability to attribute mental states such as beliefs and desires to other people has been proposed to involve simulating theirmental processes in our own brains. A new imaging study shows that predicting the actions of others does involve areas in thehuman action control system, but not the same areas that are activated when we plan to perform the same actions ourselves.

NATURE NEUROSCIENCE VOLUME 7 | NUMBER 1 | JANUARY 2004 5

Figure 1 Training phase of the associative visuomotortask. Participants learned to anticipate the actions oftheir training partner to prepare them for the subsequentfMRI experiment.

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comparison showed differential activity inparacingulate cortex and superior tempo-ral sulcus (STS), areas typically involved inmental state attribution3,6,7. The crucialquestion, then, was whether PMd, the areainvolved in one’s own action preparationfollowing specific instructions, would alsobe active following specific third-personinstruction cues. Such a result would bestrong evidence for ‘simulation theory’. Incontrast, mental state attribution througha mechanism like ‘theory theory’ shouldlead to activation in areas outside themotor system. Ramnani and Miall did notobserve activity in PMd when subjects

anticipated the action of their partner.Instead, this comparison activated twoother neural systems: areas associated withToM tasks, including paracingulate cortexand posterior superior temporal sulcus,and motor areas, including ventral premo-tor cortex (PMv).

This new study2 extends our presentknowledge of action understanding in twoways. First, by using a task that requires dor-sal premotor cortex rather than ventral pre-motor cortex, Ramnani and Miall were ableto show that the area in PMv usually associ-ated with action understanding and imita-tion (BA 44/45), is involved in actionprediction, even when it is not part of thesubsystem used for action planning.Previous studies of action understandinghave used standard visuomotor stimulus-response tasks, which involve PMv. Thus, inthese studies, PMv was activated duringaction execution and action observation.

Accordingly, the results from these studiessuggested that a common neural mecha-nism may underlie the planning of actionsand the observation or anticipation of theseactions, supporting simulation theory8.Ramnani and Miall’s results show that PMvis activated when observing someone elsemaking an action, even though execution ofthat same action activates PMd.

Ramnani and Miall suggest two possibleinterpretations of the co-activation of STSand PMv. On the one hand, it could be thatone predicts the other’s action by first simu-lating the execution of the action oneself. Onthe other hand, forming a mental image of

the other’s action could alsoaccount for the activation inthese areas. We consider thefirst possibility unlikely. Ifsimulating an action is equiv-alent to preparing to performit oneself, then in this task weshould see activation of PMd.This was not the case. The ideathat we predict an action byimagining the other personperforming it seems moreplausible. It is believed thatPMv has a specific role inaction when a visual stimulusdirectly indicates the form ofthe action required9. This isthe case when reaching for anobject where the shape of theobject indicates the form andorientation of the handneeded for grasping, but not

when the visual stimulus is an arbitrary signas in the Ramnani and Miall experiment.However, the sight of another person per-forming an action also directly indicates theaction required to imitate the response.Indeed there are ‘mirror neurons’ in PMvthat respond during the observation of spe-cific actions10. In the Ramnani and Miallexperiment, no action could be observed,but the subjects had previously observedtheir partners responding to the cues seenduring scanning. The activity in PMv mighttherefore be associated with imagining thepartner performing the action.

The second way in which the newstudy2 extends our knowledge concernsthe way the other person’s task is repre-sented. The activation in areas typicallyengaged in mental state attribution sug-gests that an explicit representation of theother person as an intentional agent wasformed. It is generally believed that the

mirror system does not provide an explicitrepresentation of other agents or tasks11.Therefore, an additional mechanism mustbe assumed, linking particular stimuli toparticular actions. Such a link could beachieved by forming a representation of anintentional relation1. Barresi and Moore12

define intentional relations as relationsthat involve an agent (in this case, theother participant), an object (a particularstimulus) and the activity connectingagent to object (pressing a specificresponse button upon seeing the stimu-lus). Thus, a specific stimulus is associatedwith the other’s intention to act. It seemspossible that forming and holding such anintentional relation in mind relies on areasalso involved in more complex ToM tasks3.In the Ramnani and Miall study, partici-pants were encouraged to pay attention tothe other’s actions through a monitoringtask. Evidence from studies on task repre-sentation when two people act at the sametime suggests that an intentional relationmay be formed even when there is no needto take the other agent into account13. Itwould be interesting to find out whethersimilar results can be obtained in theabsence of a monitoring task that encour-ages mentalizing about the other person.Finally, investigating individuals withautism in the task developed by Ramnaniand Miall seems like a promising way toaddress the question of whether the ToMdeficits in individuals with autism arerestricted to the attribution of complexmental states to others or also affect therepresentation of intentional relations14.

1. Gallese, V. & Goldman, A. Trends Cogn. Sci. 2,493–501 (1998).

2. Ramnani, N. & Miall, R.C. Nat. Neurosci. 7, 85–90(2004).

3. Gallagher, H.L. & Frith, C. Trends Cogn. Sci. 7, 77–83(2003).

4. Grafton, S.T. et al. J. Neurophysiol. 79, 1092–1097(1998).

5. Gallagher, H.L. et al. Neuroimage 16, 814–821(2002).

6. Frith, U. & Frith, C.D. Phil. Trans. R. Soc. Lond. B Biol.Sci. 358, 459–473 (2003).

7. Saxe, R. et al. Annu. Rev. Psychol. (in press).8. Blakemore, S.-J. & Decety, J. Nat. Rev. Neurosci. 2,

561–567 (2001).9. Fogassi, L. et al. Brain 124, 571–586 (2001).10. Rizzolatti, G. et al. Nat. Rev. Neurosci. 2, 661–670

(2001).11. Knoblich, G. & Jordan, S. in Proceedings of the 22nd

Annual Conference of the Cognitive Science Society(eds. Gleitman, L.R. & Joshi, A.K.) 764–769 (Erlbaum,Hillsdale, NJ, 2000).

12. Barresi, J. & Moore, C. Behav. Brain Sci. 19, 107–154(1996).

13. Sebanz, N. et al. Cognition 8, 11–21 (2003).14. Sebanz, N. et al. J. Cogn. Neuropsychol. (in press).

6 VOLUME 7 | NUMBER 1 | JANUARY 2004 NATURE NEUROSCIENCE

"The crucial question, then,was whether dorsalpremotor cortex, the areainvolved in one’s own actionpreparation followingspecific instructions, wouldalso be active followingspecific third-personinstruction cues... "

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