Visual activity in areas V3a and V3 during reversible inactivation of area V1 in the macaque monkey.

1. Behavioral studies in the monkey and clinical studies in humans show that some visuomotor functions are spared in case of a V1 lesion. This residual vision appears to be subserved at least partially by visual activity in extrastriate cortex. Earlier studies have demonstrated that neurons in area V2 lose their visual responses when V1 is reversibly inactivated. On the other hand, Rodman and collaborators have recently shown that neurons in the middle temporal area (area MT) remain visually responsive when V1 is lesioned or inactivated. The purpose of the present study was to determine whether area MT is unique among extrastriate cortical areas in containing visually responsive neurons in the absence of input from area 17. 2. A circular part of the opercular region of area V1 was reversibly inactivated by cooling with a Peltier device. In that condition, 149 sites were recorded in the retinotopically corresponding regions of areas V3 and V3a. 3. About 30% of sites in area V3a still responded to visual stimulation when V1 was inactivated. On the contrary, nearly all sites in area V3 ceased to fire to visual stimulation. Receptive-field properties were assessed with qualitative measures; for most single cells or multiunit sites that responded during V1 inactivation, these properties did not change during cooling. 4. These results suggest that area V3a could take part in spared visuomotor abilities in case of a lesion of V1. Areas V3a and MT are both part of the occipitoparietal pathway, which suggests that the residual vision observed after a lesion of area 17 may depend mostly on this pathway.