Early coding of visuomanual coordination during reaching in parietal area PEc.

The parietal mechanisms of eye-hand coordination during reaching were studied by recording neural activity in area PEc while monkeys performed different tasks, aimed at assessing the influence of retinal, hand-, and eye-related signals on neural activity. The tasks used consisted of 1) reaching to foveated and 2) to extra-foveal targets, with constant eye position; and 3) saccadic eye movement toward, and holding of eye position on peripheral targets, the same as those of the reaching tasks. In all tasks, hand and/or eye movements were made from a central position to eight peripheral targets. A conventional visual fixation paradigm was used as a control task, to assess location and extent of visual receptive field of neurons. A large proportion of cells in area PEc displayed significant relationships to hand movement direction and position. Many of them were also related to the eye's position. Relationships to saccadic eye movements were found for a smaller proportion of cells. Most neurons were tuned to different combination of hand- and eye-related signals; some of them were also influenced by visual information. This combination of signals can be an expression of the early stages of the composition of motor commands for different forms of visuomotor coordination that depend on the integration of hand- and eye-related information. These results assign to area PEc, classically considered as a somatosensory association cortex, a new visuomotor role.