Three-dimensional tuning profile of motor cortical activity during arm movements.

The neural firing activity in the primary motor cortex was modulated to the direction of hand movement. In contradiction to previous reports, a recent study found a non-uniform distribution of preferred directions of neurons while monkeys made center-out reaching movements in a horizontal plane. To re-examine the distribution of preferred directions in three-dimensional space, we recorded the activity of 117 arm-related neurons in the primary motor cortex and electromyographic signals of shoulder and upper arm muscles of a monkey while it performed center-out reaching movements towards 26 target points placed on a sphere-shaped workspace. We found that the distribution of preferred directions of neurons was non-uniform and that it was correlated to muscle activity and arm joint rotations.