BRAIN ACTIVITY DURING OBSERVATION OF ACTIONS - INFLUENCE OF ACTION CONTENT AND SUBJECTS STRATEGY

PET was used to map brain regions that are associated with the observa tion of meaningful and meaningless hand actions. Subjects were scanned under four conditions which consisted of visually presented actions. In each of the four experimental conditions, they were instructed to w atch the actions with one of two aims: to be able to recognize or to i mitate them later We found that differences in the meaning of the acti on, irrespective of the strategy used during observation lead to diffe rent patterns of brain activity and clear left/right asymmetries. Mean ingful actions strongly engaged the left hemisphere in frontal and tem poral regions while meaningless actions involved mainly the right occi pitoparietal pathway. Observing with the intent to recognize activated memory-encoding structures. In contrast, observation with the intent to imitate was associated with activation in the regions involved in t he planning and in the generation of actions. Thus, the pattern of bra in activation during observation of actions is dependent both on the n ature of the required executive processing and the type of the extrins ic properties of the action presented.