Monkey pyramidal tract neurons and changes of movement parameters in visual tracking.
During a single-step visual tracking task of monkeys, parametric changes of the wrist extension-flexion movement and related discharge rate changes of pyramidal tract neurons (PTNs) of hand-arm motor area were studied. The task consisted of preparatory, precontraction, contraction and target periods. If the displacement amplitude was changed from narrow (10-20 degrees) to moderate (40 degrees) range, peak velocity, peak acceleration and contraction period increased linearly but precontraction period decreased slightly. In 61 movement-related PTNs, no linear relationships were found between PTN discharge rate during precontraction or contraction period and displacement amplitude, velocity, acceleration, precontraction period or contraction period. In less than 20% of PTNs, however, correlations between PTN discharge rate during precontraction period and velocity or acceleration were found in the moderate range task. It occurred less frequently in narrow range task. It is said in a visual tracking task that PTN activity is not dependent upon factors related to the task parameters, such as velocity, acceleration. Possible related factors were discussed.