Preparatory activity in PMd neurons to bypass a virtual obstacle in the reaching path

We recorded neural activities in dorsal premotor areas (PMd) when monkey was preparing to perform arm reaching movements in motor-set period before his actual execution. He was required to select one of four possible movements (reaching a target on the top-left or top-right corner of a virtual cube, moving straightly or making a detour) in accordance with two sets of instruction cues. Among the neurons recorded, we analyzed 118 neurons which showed set activities during movement preparation. More specifically, 46 neurons were modulated with respect to the obstacle-related conditions;42 neurons, with respect to target location and 15 were tuning to both. In trials in which the virtual obstacle appeared, successful trials were also compared to unsuccessful (hit-obstacle) trials, in which the monkey moved straight to the target instead of bypassing the virtual obstacle. The motor-set activity of a specific group of neurons was significantly different in set activities between successful and unsuccessful trials. Their activity was strongly modulated by the spatial position of the virtual obstacle, indicating that those cells likely participated in the planning of the hand path (straight or curved in counterclockwise direction) based on visual information about the virtual obstacle. At the same time, neurons in which the spike activity modulation with respect to the virtual obstacle position was relatively weak, did not show significant differentiation of the motor-set, preparatory activity between successful and unsuccessful trial types.