MAGNOCELLULAR AND PARVOCELLULAR CONTRIBUTIONS TO THE RESPONSES OF NEURONS IN MACAQUE STRIATE CORTEX

Anatomical and physiological studies of the primate visual system have suggested that the signals relayed by the magnocellular and parvocell ular subdivisions of the LGN remain segregated in visual cortex. It ha s been suggested that this segregation may account for the known diffe rences in visual function between the parietal and temporal cortical p rocessing streams in extrastriate visual cortex. To test directly the hypothesis that the temporal stream of processing receives predominant ly parvocellular signals, we recorded visual responses from the superf icial layers of V1 (striate cortex), which give rise to the temporal s tream, while selectively inactivating either the magnocellular or parv ocellular subdivisions of the LGN. Inactivation of the parvocellular s ubdivision reduced neuronal responses in the superficial layers of V1, but the effects of magnocellular blocks were generally as pronounced or slightly stronger. Individual neurons were found to receive contrib utions from both pathways. We furthermore found no evidence that magno cellular contributions were restricted to either the cytochrome oxidas e blobs or interblobs in V1. Instead, magnocellular signals made subst antial contributions to responses throughout the superficial layers. T hus, the regions within V1 that constitute the early stages of the tem poral processing stream do not appear to contain isolated parvocellula r signals. These results argue against a direct mapping of the subcort ical magnocellular and parvocellular pathways onto the parietal and te mporal streams of processing in cortex.