Multi-electrode recordings in the macaque parietal cortex reveal common processing of eye-, arm- and hand movements

Hand actions are usually performed in coordination with eye movements. For example, the grasp site on an object is invariably fixated prior to grasping. However, the neural basis of eye-hand coordination in object manipulation is not well understood. Previous studies have shown that parietal regions such as MIP, LIP and AIP may play a pivotal role. The latter areas are involved in controlling different effectors such as the eye, arm and hand, but it is not clear how these different areas interact during naturalistic behavior involving eye, reach and grasping movements. Two monkeys were trained in a sequential saccade-reach-grasp task, in which the animals initiated a trial by fixating a spot on a display, which was followed by the illumination of an object in peripheral vision. After a variable delay, the fixation spot dimmed, indicating to the animals to make a saccadic eye movement to the illuminated object. A second go-cue instructed the animals to reach towards, grasp and pull the object. Both animals were implanted with a chronic 96-channel microdrive (Gray Matter Research) with individually-movable electrodes above parietal cortex, allowing access to AIP, MIP, LIP, area 5 and PFG. We recorded in 171 sessions (monkey S: 87; 4187 recording sites, monkey O: 84 sessions; 4544 recording sites), and the electrode position was confirmed by repeated CT-MRI co-registration in which individual electrodes could be visualized. We found significant task-related multi-unit activity in 1460 sites (monkey O: 798 sites, monkey S: 662). A minority of these recording sites was responsive during object illumination (monkey O: 293 sites, monkey S: 167), and these recording sites were typically located more anteriorly in the IPS. On the majority of channels, however, we obtained an initial sustained increase in neural activity after saccade onset followed by an additional increase in activity in the epoch before the hand started moving towards the object. We did not observe a clear separation of saccade-, reach- and grasp-related activity across parietal cortex. In contrast, we observed very similar response profiles in all parietal areas. These results suggest that parietal areas work in concert during a saccade-reach-grasp task that mimics natural prehension behavior.status: publishe