Responses of monkey precentral cortical cells during a controlled jaw bite task.

Publisher Website
Google Scholar
Abstract
Single-unit discharges were recorded in the precentral face area of rhesus monkeys Macaca mulatta trained to exert steady biting forces of about 1-70 N for 1.5-2 s. Neurons (100) increased their discharge rates before or shortly after the onset of isometric jaw force. Generally, the rate at the beginning of the response was higher than later in the bite. Another 53 units decreased their discharge rates during task performance. Of 59 cells, 15 discharged more rapidly during more forceful bites, particularly for low biting forces: a result was reported for precentral cells in the forelimb area with respect to the force of wrist and finger movements. Precentral cortex may be important in controlling the strength of muscular contraction. Sinusoidal movements at frequencies between 5 and 30 Hz and at a constant .+-. 500-.mu.m amplitude were applied to the jaw during biting. The resultant changes in jaw position and jaw force modulated the discharge rates of about 70% of the activated cells. The amplitude and phase characteristics of the responses of a small group of extensively studied neurons are consistent with a muscle spindle projection to these cells. Only a relatively small proportion of task-related cell discharged in relation to the cyclical and vigorous activation of jaw muscles during chewing, suggesting that the rhythm of chewing may be patterned elsewhere in the brain. Single-pulse, low-intensity (.ltoreq. 100 .mu.A) intracortical microstimulation produced bilateral inhibition of jaw-closing muscle activity at short latencies (about 7 ms). Microstimuli applied in a few penetrations adjacent to the central sulcus produced short-latency excitation of contralateral masseter muscle activity, and inhibition of activity in other jaw-closing muscles. Task-related cells were found only within the cortical area in which microstimulation produced effects on jaw muscles at currents of 100 .mu.A or less.