Patterns of muscular and motor cortical activity during a simple arm movement in the monkey

This article describes the behavior of motor cortex neurons recorded in macaque monkeys (Macaca mulatta) which had been trained to make extension and flexion movements about the elbow in response to auditory, visual, or somesthetic cues. The pattern of activity of 65% of those movement-related neurons which were recorded during both flexion and extension was reciprocally related to the direction of movement. However, the movements of extension and flexion were made by co-contraction of the biceps and triceps in a pattern that did not match that of the motor cortex neurons. The majority of motor cortex neurons had firing frequencies that were related to movement parameters but by their nature could not be directly involved in the control of alpha motoneurons in both directions of movement. We suggest that they could, instead, control the fusimotor system. It is more likely that alpha motoneurons are controlled by the 35% of motor cortex neurons that, like the muscles, do not show reciprocal patterns of activity for movements in opposite directions.