Motor cortical activity during sinusoidal tracing

Single cell activity recorded from the proximal arm area of motor cortex during the performance of arm reaching tasks can be related to the direction of movement. This was found for single straight movements made directly to a target and for movements in which direction changed continually. Responses from a population of 2 2 6 directionally-sensitive cells were combined to form neural images of the trajectory. The construction of these images suggests that trajectory-related information in the motor cortex is generated incrementally throughout the task and is coded in an instantaneous coordinate system. The motor cortex historically has been considered important in controlling volitional behavior. This is interesting because the recording of cellular activity from the motor cortex during volitional movement has taken place only within the last 20 years. This region of cerebral cortex was implicated in volitional control many years before the first recordings in experiments that used lesions or electrical stimulation in anesthetized animals. In primates, lesions of primary motor cortex result in minor movement deficits, mostly confined to the distal extremities (deficit in precision grip). Electrical activation of motor cortex results in movements that at best produce compound muscle contractions at one or two joints. Most of the time, such activation results in twitchlike contractions in one or several muscles. Beginning in the late 1 9 6 0 s studies comparing motor cortical activity to volitional movements were designed to examine movement about a single joint. Animals were rewarded for flexing or extending the elbow or wrist. These studies showed that single cell activity was related to the force used to accomplish the task in a certain direction (flexion or extension). In the late 1970s and early 1980s, motor cortical physiologists began to look at unrestrained, multi-joint movements. One of these studies, (2) used a task in which the animal moved a freely movable handle over a surface. The animals were rewarded for moving the handle from a target in the center of the surface to one of eight radially-oriented targets. These trajectories were relatively straight, so the movements were made in eight equally spaced directions. Many cells recorded in the proximal arm area of motor cortex were found to have discharge rates related to the direction of movement. The discharge rate was averaged over each trial from the time the radial target was presented (go) to the time the