Andreas S. Tolias, Tirin Moore and Peter H. Schiller
Dept. of Brain and Cognitive Sciences, MIT
The goal of this study is to characterize the influence of eye movements on the visual responses of neurons in area V4. Methods: We recorded the extracellular activity of neurons within the prelunate gyrus of the monkey while it performed a visually guided saccade task. After the monkey acquired fixation, a visual stimulus, which could drive the cell reliably when flashed in its receptive field, was presented at one of many possible locations on a CRT monitor. Following a delay of 350-500 msec, a saccade target appeared and the monkey was rewarded for making a saccadic eye movement to it. On some trials the visual stimulus and the saccade target were positioned in such a way that the visual stimulus would fall into the receptive field following the saccade. On the other trials the stimulus would either fall far from the receptive field or no visual stimulus would appear during the trial. Results: Similar to what has previously been reported (Fischer and Boch 1981), we find that cells in V4 can show enhancement of their responses before the onset of saccades. In addition we observe that: a) The presaccadic enhancement depends both on the presence and the position of the visual stimulus. b) The presaccadic enhancement also depends on the vector of the saccade. Conclusion: These results indicate that cells in area V4 do not merely respond to the retinal input, but are influenced by the planning of eye movements or the integration of the two. We are aware of the possibility that the presaccadic activity may reflect a change in the focus of attention during eye movements. We are in the process of mapping the visual stimulus positions that give rise to the presaccadic enhancement for different saccade vectors.