Saccade-related activity in the parietal reach region.

In previous experiments, we showed that cells in the parietal reach region (PRR) in monkey posterior parietal cortex code intended reaching movements in an eye-centered frame of reference. These cells are more active when an arm compared with an eye movement is being planned. Despite this clear preference for arm movements, we now report that PRR neurons also fire around the time of a saccade. Of 206 cells tested, 29% had perisaccadic activity in a delayed-saccade task. Two findings indicate that saccade-related activity does not reflect saccade planning or execution. First, activity is often peri- or postsaccadic but seldom presaccadic. Second, cells with saccade-related activity were no more likely to show strong saccadic delay period activity than cells without saccade-related activity. These findings indicate that PRR cells do not take part in saccade planning. Instead, the saccade-related activity in PRR may reflect cross-coupling between reach and saccade pathways that may be used to facilitate eye-hand coordination. Alternatively, saccade-related activity may reflect eye position information that could be used to maintain an eye-centered representation of intended reach targets across eye movements.