Visual, saccade-related, and cognitive activation of single neurons in monkey extrastriate area V3A.

Area V3A is an extrastriate visual area that provides a major input to parietal cortex. To identify the sensory, saccade-related, and cognitive signals carried by V3A neurons, we recorded from single units in alert monkeys during performance of fixation and memory guided saccade tasks. We found that visual responses to stationary stimuli in area V3A were affected by the behavioral relevance of the stimulus. The amplitude of the visual response differed between the memory-guided saccade task, in which the monkey had to use the information provided by the stimulus to guide its behavior, and the fixation task. For 18% (29/163) of V3A neurons, the response was significantly enhanced in the memory-guided saccade task as compared with that in the fixation task. For 8% (13/163) of V3A neurons, the amplitude of response in the memory-guided saccade task was significantly suppressed. We also observed task-related modulation of activity prior to stimulus onset. Among the V3A neurons (37/163) that showed significant differences between tasks in prestimulus activity, the majority (89%; 33/37) showed greater prestimulus activity in the memory-guided saccade task. Task-related increases in prestimulus activity in the memory-guided saccade task were not always matched by increases in the sensory response, indicating that visual responses and prestimulus activity can be modulated independently. Activity in the memory period was suppressed compared with prestimulus activity for 83% (49/59) of the V3A neurons that showed a significant difference in activity (59/197) between these two epochs. For some neurons, memory-period activity dropped even below the baseline level in the fixation task, indicating that there may be an active suppression mechanism. Many V3A neurons (75%, 148/197) also had activity in the saccade epoch. This activity was most prominent immediately after the saccade. Postsaccadic activity was observed even when testing was carried out in total darkness, indicating that this activity reflects, at least in part, extraretinal signals and is not simply a response to visual reafference. These results indicate that several kinds of signals are carried by single neurons in extrastriate area V3A. Moreover, activity in V3A is subject to modulation by extraretinal factors, including attention, anticipation, memory, and saccadic eye movements.