Abstract
To elucidate functional roles of primary motor cortex (M1) in the control of locomotor movements in primates, we recorded activity of M1 neurons in a freely moving monkey. The animal walked quadrupedally on the treadmill belt moving at various constant speeds. We tested effects of the walking speed on the neuronal discharge pattern. During simple locomotion, almost all neurons (33/34) exhibited task-related modulation. Of these, 23 neurons modulated their discharge phasically, and 8 did phasically and tonically time-locked to the step cycle. The rest modulated tonically. At the speed of 1.0 m/s, mean discharge frequency of task-related neurons was 18.6 ± 2.3 spikes/s. For neurons showing phasic and phasic-tonic modulation, the peak activity occurred once or twice at widely different times during the step cycle. Frequency of the peak activity ranged from 17.4 to 98.4 spikes/s (mean 42.2 ± 4.4 spikes/s). Of the task-related neurons, 21 were tested for the effects of treadmill speed on their discharge patterns. For locomotion at speeds between 0.7 and 1.3 m/s, more than two thirds of neurons (15/21) increased or decreased mean and/or peak discharge frequency along with an increase of the speed. All these results suggest the possibility that output of the primary motor cortex in macaque monkeys directly and/or indirectly acts on spinal circuitries generating a basic pattern of rhythmic activity during simple locomotion in a manner different from that in subprimates. [J Physiol Sci. 2008;58 Suppl:S192]
