Neuronal clusters in the primate motor cortex during interception of moving targets

Two rhesus monkeys were trained to intercept a moving target at a fixed loc ation with a feedback cursor controlled by a 2-D manipulandum. The directio n from which the target appeared, the time from the target onset to its arr ival at the interception point, and the target acceleration were randomized for each trial, thus requiring the animal to adjust its movement according to the visual input on a trial-by-trial basis. The two animals adopted dif ferent strategies, similar to those identified previously in human subjects . Single-cell activity was recorded from the arm area of the primary motor cortex in these two animals, and the neurons were classified based on the t emporal patterns in their activity, using a nonhierarchical cluster analysi s. Results of this analysis revealed differences in the complexity and dive rsity of motor cortical activity between the two animals that paralleled th ose of behavioral strategies. Most clusters displayed activity closely rela ted to the kinematics of hand movements. In addition, some clusters display ed patterns of activation that conveyed additional information necessary fo r successful performance of the task, such as the initial target velocity a nd the interval between successive submovements. suggesting that such infor mation is represented in selective subpopulations of neurons in the primary motor cortex. These results also suggest that conversion of information ab out target motion into movement-related signals takes place in a broad netw ork of cortical areas including the primary motor cortex.