Effects of stimulation of corpus callosum on precentral neuron activity in the awake monkey

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Abstract
The effects of stimulation of the corpus callosum (CC) on precentral neurons were studied in monkeys performing motor tasks with either forelimb. Of a total of 246 precentral neurons that were tested with CC stimulation, 70 were orthodromically and 12 were antidromically activated. The percentages of neurons orthodromically activated by CC stimulation were the same in pyramidal tract neurons (PTNs) (31%) and non-PTNs (31%). The mean latency of neuronal activation by CC stimulation was similar in PTNs and non-PTNs. Precentral neurons were divided into two groups with respect to muscular contractions evoked by intracortical stimulation: neurons related to finger, wrist, and elbow movements (distal group) and those related to shoulder or axial movements (proximal group). The percentages of neurons orthodromically activated by CC stimulation were similar in both groups; 25% in distal and 29% in proximal groups. However, the mean latency of orthodromic CC activation was significantly shorter for the proximal than for the distal group. Precentral neurons were classified into three groups; neurons related to finger and/or wrist movement tasks (F-W group), those related to arm movement tasks in addition to finger and/or wrist tasks (F, W + A group), and those related to arm movements only (A group). The percentages of neurons orthodromically activated by CC stimulation were similar in the three groups. The mean latencies of neuronal activities were a little longer in the F-W group than in the A group or the F, W + A group. Precentral neurons were classified into three groups in relation to ipsilateral or contralateral forelimb movements: neurons related to ipsilateral movements (ipsi neurons, n = 13), those related to ipsilateral as well as contralateral movements (bilat neurons, n = 50) and those related to contralateral movements (contra neurons, n = 136). The percentages of neurons orthodromically activated by CC stimulation were 15 (2/13, ipsi neurons), 24.0 (12/50, bilat neurons), and 25.0% (34/136, contra neurons), respectively. The mean latencies of neuronal activation were compared between two groups; one group was composed of ipsi and bilat neurons, and the other group was of contra neurons. The mean latency was a little shorter for the ipsi + bilat group than for the contra group.(ABSTRACT TRUNCATED AT 400 WORDS)