To test the functional implications of gaze signals that we previously reported in the dorsal premotor cortex (PMd), we trained
two rhesus monkeys to point to visual targets presented on a touch screen while controlling their gaze orientation. Each monkey
had to perform four different tasks. To initiate a trial, the monkey had to put his hand on a starting position at the center
of the touch screen and fixate a fixation point. In one task, the animal had to make a reaching movement to a peripheral target
randomly presented at one of eight possible locations on a circle while maintaining fixation at the center of this virtual
circle (central fixation + reaching). In the second task, the monkey maintained fixation at the location of the upcoming peripheral
target and, later, reached to that location. After a delay, the target was turned on and the monkey made a reaching arm movement
(target fixation + reaching). In the third task, the monkey made a saccade to the target without any arm movement (saccade).
Finally, in the fourth task, the monkey first made a saccade to the target, then reached to it after a delay (saccade + reaching).
This design allowed us to examine the contribution of the oculomotor context to arm-related neuronal activity in PMd. We analyzed
the effects of the task type on neuronal activity and found that many cells showed a task effect during the signal (26/60;
43%), set (16/49; 33%) and/or movement (15/54; 28%) epochs, depending on the oculomotor history. These findings, together
with previously published data, suggest that PMd codes limb-movement direction in a gaze-dependent manner and may, thus, play
an important role in the brain mechanisms of eye-hand coordination during visually guided reaching.
Key words Premotor cortex - Eye-hand coordination - Single-unit recording - Monkey - Arm movement
Context
Received: 10 September 1998 / Accepted: 19 March 1999