Abstract

In this study we examined the temporal relationships of the eye movement-related activities of the visual cortical areas 17 and 18 with the saccade onset and offset times in three awake cats. Eye positions were monitored with the scleral search-coil technique, and single or multiple unit activities were recorded with conventional electrophysiological methods while cats were spontaneously making saccades in the dark. Saccade onset and offset times were determined according to velocity criteria. Based on the sequence of action potentials, the spike probability density was estimated by a variable kernel method and the onset of neural activity was determined with a spike density threshold. When all 666 saccade-related activities of 59 recording sites were combined, the lag between the onset of neural activity and the saccade onset time was linearly correlated with saccade duration(slope of linear regression line was 1.01). On the other hand, the lag between the onset of neural activity and the saccade offset was independent of saccade duration(slope of linear regression line was 0.01), with the saccade offset leading the onset of neural activity by 46ms on average. Thus, eye movement-related cortical activity was more tightly related to saccade offset than onset time. These results suggested that the eye movement-related signals integrated in the visual cortex might play a perceptual role rather than corollary discharge of eye movement commands as previously assumed.