DOC PREVIEW
Princeton COS 598B - Neurophysiological mechanisms underlying the understanding and imitation of action

This preview shows page 1-2-3 out of 10 pages.

Save
View full document
View full document
Premium Document
Do you want full access? Go Premium and unlock all 10 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 10 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 10 pages.
Access to all documents
Download any document
Ad free experience
Premium Document
Do you want full access? Go Premium and unlock all 10 pages.
Access to all documents
Download any document
Ad free experience

Unformatted text preview:

© 2001 Macmillan Magazines LtdPERSPECTIVESthe article, when we discuss imitation andunderstanding of meaning.What are the neural mechanisms thatunderlie action understanding? By actionunderstanding, we mean the capacity toachieve the internal description of an actionand to use it to organize appropriate futurebehaviour. Broadly speaking, there are twohypotheses that might explain how actionunderstanding occurs. The first one, which wewill refer to as the ‘visual hypothesis’, statesthat action understanding is based on a visualanalysis of the different elements that form anaction, and that no motor involvement isrequired. For example, when we observe ahand grasping an apple, the analysed elementswould be the hand, the apple and the move-ment of the hand towards the apple. The asso-ciation of these elements, and inferences abouttheir interaction, would be sufficient to allowthe observer to understand the witnessedaction. If this view were correct, action under-standing would essentially be mediated by theactivity of the extrastriate visual areas, theinferotemporal lobe and the superior temporalsulcus (STS). In both monkeys and humans,these areas respond selectively to objects,body parts, biological motion and, in the caseof some neurons of the STS, interactionsbetween hands and objects1–7.An alternative hypothesis, which we willrefer to as the ‘direct-matching hypothesis’,holds that we understand actions when wemap the visual representation of the observedaction onto our motor representation of thesame action. According to this view, an actionis understood when its observation causes themotor system of the observer to ‘resonate’. So,when we observe a hand grasping an apple,the same population of neurons that controlthe execution of grasping movementsbecomes active in the observer’s motor areas.By this approach, the ‘motor knowledge’ ofthe observer is used to understand theobserved action. In other words, we under-stand an action because the motor representa-tion of that action is activated in our brain.This view, although defended by some theo-reticians, was never particularly popular inneuroscience. However, the idea that weunderstand others through an ‘internal act’that recaptures the sense of their acting wasdefended by several philosophers, especiallyby PHENOMENOLOGISTS (for example, REF. 8;seeREF. 9 for a detailed account). Of course, thehypothesis that action understanding is basedon a direct-matching mechanism does notexclude the possibility that other, more cogni-tive processes based on object and movementdescriptions could also participate in thisfunction. It stresses, however, the primacy of adirect matching between the observation andexecution of action.Here we will review evidence that an actionobservation/execution matching system doesexist in monkeys and humans, and will dis-cuss its implications for the understanding andimitation of action.Mirror system in monkeysMirror neurons are a particular class of visuo-motor neurons, originally discovered in a sec-tor of the ventral premotor cortex of monkeys,called area F5 (REFS 10,11). Area F5 is character-ized by the presence of neurons that code goal-related motor acts such as hand and mouthgrasping12–14. Some of these cells are motorneurons, others also respond to visual stimuli.Some of them are activated by the presentationof three-dimensional objects, whereas others— mirror neurons — require action observa-tion for their activation. The main functionalcharacteristic of mirror neurons is that theyWhat are the neural bases of actionunderstanding? Although this capacitycould merely involve visual analysis of theaction, it has been argued that we actuallymap this visual information onto its motorrepresentation in our nervous system. Herewe discuss evidence for the existence of asystem, the ‘mirror system’, that seems toserve this mapping function in primates andhumans, and explore its implications for theunderstanding and imitation of action.We live in a world full of objects, sounds andmovements. Among all of these stimuli, themovements of other living creatures — espe-cially of our conspecifics — are particularlyimportant for us. How do we understand theactions of other subjects? What are the neuro-physiological bases of this ability? Unlikeother cognitive capacities, such as objectrecognition or space perception, actionunderstanding has never been a main focusof research in neuroscience, despite its crucialrole in social behaviour. Action is a rathergeneric term that describes several differenttypes of phenomenon, ranging from a move-ment directed to attain a specific goal, tobehaviours in which means and ends aretemporally far apart. In this article, we willuse the term action in two ways: as a genericterm that indicates any type of intentionalmotor behaviour, and as a specific term refer-ring to goal-directed behaviours that pro-duce a reward for the acting individual. Thisdistinction will become relevant later in NATURE REVIEWS | NEUROSCIENCE VOLUME 2 | SEPTEMBER 2001 | 661Neurophysiological mechanismsunderlying the understanding and imitation of actionGiacomo Rizzolatti, Leonardo Fogassi and Vittorio GalleseOPINION© 2001 Macmillan Magazines Ltd662 | SEPTEMBER 2001 | VOLUME 2 www.nature.com/reviews/neuroPERSPECTIVESthem include grasping, bimanual interaction,holding, placing and reaching. About half ofthe action-observation neurons responds toone action only, whereas the other halfresponds to two actions (for example, grasp-ing and releasing, see FIG. 2). But the mostimportant finding was that most neuronsthat were responsive to action observationalso discharged during action execution.They were therefore defined as PF mirrorneurons23,24. As in the case of F5, there was aclear relationship in most PF mirror neuronsbetween the observed action they respondedto and the executed action that triggeredtheir discharge.It therefore seems that there are threeinterconnected areas in the monkey brainthat contain neurons that are responsive tobiological movements. These areas differ intheir motor properties. In F5, almost all ofthese neurons discharge during action execu-tion. In area PF, about two-thirds of themhave this characteristic. In the STSa, neuronswith motor properties do not seem to becommon, although, as mentioned above, nosystematic investigation of motor propertiesin STSa has been carried out so far.However, it is important to stress thatthese findings do not exclude the


View Full Document

Princeton COS 598B - Neurophysiological mechanisms underlying the understanding and imitation of action

Documents in this Course
Lecture

Lecture

117 pages

Lecture

Lecture

50 pages

Load more
Download Neurophysiological mechanisms underlying the understanding and imitation of action
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view Neurophysiological mechanisms underlying the understanding and imitation of action and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Neurophysiological mechanisms underlying the understanding and imitation of action 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?