Abstract
In Japanese monkeys, our PET study has shown that the primary motor cortex (M1) is activated bilaterally during quadrupedal (Qp) locomotion. We have also shown that unilateral injection of muscimol into M1 hindlimb region produced claudication in the hindlimb contralateral to the injection side. To further examine M1 mechanisms related to the control of Qp locomotion in primates, we recorded neuronal activity in M1 of a monkey walking quadrupedally on the treadmill. Four micro-electrodes were simultaneously implanted into M1 hindlimb region using 4-channel, custom-made micromanipulator. Each electrode was advanced independently and screened daily for single-unit action potentials for up to 2 weeks. Extracellular recordings were made during the execution of quadrupedal locomotion. The treadmill speed was increased or decreased over a range of 0.4-1.6 m/s. The walking animal was videotaped to determine stance and swing phases within a single step cycle. Most units were recordable for more than 2 hours. We found that M1 neurons phasically modulated their discharge time-locked to the step cycle. Most of them showed a roughly linear relationship between peak discharge rate and treadmill speed. These results suggest that M1 output in monkeys directly and/or indirectly acts on spinal circuitries generating a basic pattern of rhythmic activity during simple Qp locomotion in a manner different from that in subprimates. [Jpn J Physiol 55 Suppl:S175 (2005)]
