DIRECT VISUAL PATHWAYS FOR REACHING MOVEMENTS IN THE MACAQUE MONKEY

THE brain seems to process the location of objects faster than their i ntrinsic features, such as size, when these parameters are used to gui de action. To uncover a potential anatomical substrate of these differ ent processing speeds, we investigated in the monkey the pathways link ing extrastriate visual cortex with the dorsal premotor area, a fronta l area known to be involved in visually guided reaching movements. Ret rogradely transported anatomical tracers were injected at physiologica lly defined sites and the distribution of labelled cells was examined in the ipsilateral cortex. We found a projection to the dorsal premoto r cortex from the parieto-occipital area (PO). This area receives dire ct projections from the primary visual cortex (V1), and is part of the dorsal visual stream involved in the processing of spatial informatio n. No direct projections to the dorsal premotor cortex arise from the ventral visual areas, thought to process object features. Our finding provides evidence for direct pathways from the dorsal visual stream to the dorsal premotor cortex and supports the view that the location of objects is processed faster by the brain than their intrinsic feature s.