Top down effect of strategy on the perception of human biological motion: a pet investigation.

This experiment was designed to investigate the neural network engaged by the perception of human movements using positron emission tomography. Perception of meaningful and of meaningless hand actions without any purpose was contrasted with the perception of the same kind of stimuli with the goal to imitate them later. A condition that consisted of the perception of stationary hands served as a baseline level. Perception of meaningful actions and meaningless actions without any aim was associated with activation of a common set of cortical regions. In both hemispheres, the occipito-temporal junction (Ba 37/19) and the superior occipital gyrus (Ba 19) were involved. In the left hemisphere, the middle temporal gyrus (Ba 21) and the inferior parietal lobe (Ba 40) were found to be activated. These regions are interpreted as related to the analysis of hand movements. The precentral gyrus, within the area of hand representation (Ba 4), was activated in the left hemisphere. In addition to this common network, meaningful and meaningless movements engaged specific networks, respectively: meaningful actions were associated with activations mainly located in the left hemisphere in the inferior frontal gyrus (Ba 44/45) and the fusiform gyrus (Ba 38/20), whereas meaningless actions involved the dorsal pathway (inferior parietal lobe, Ba 40 and superior parietal lobule, Ba 7) bilaterally and the right cerebellum. In contrast, meaningful and meaningless actions shared almost the same network when the aim of the perception was to im itate. Activations were located in the right cerebellum and bilaterally in the dorsal pathway reaching the prem otor cortex. Additional bilateral activations were located in the SMA and in the orbitofrontal cortex during observation of meaningful actions.