LARGE-SCALE MOTOR MAINTENANCE NETWORK IN MACAQUE CEREBRAL CORTEX

S.L. Bressler¹; M. Ding¹; H. Liang²; R. Nakamura³

During maintenance of a steady grip, the primary motor cortex exhibits Local Field Potential (LFP) oscillations in the beta frequency range (13-30 Hz) that are synchronized with cortical pyramidal tract neuron firing and electromyographs of contralateral hand and forearm muscles (Baker et al. Exp Brain Res 1999). To investigate the large-scale organization of LFP oscillations in the beta frequency range during motor maintenance, LFPs were recorded from the cortex of one cerebral hemisphere in macaque monkeys as they performed a visuomotor pattern discrimination task. In the prestimulus period, the monkeys maintained pressure on a lever with the contralateral hand while also monitoring a display screen in anticipation of stimulus presentation. We found that beta frequency LFP oscillations were selectively synchronized among sites in posterior parietal, somatosensory and motor cortices during the period prior to stimulus processing, suggesting that the primary motor cortex cooperates with these other areas in a large-scale network in the maintenance of steady motor outputs. We further observed that the strength of beta frequency LFP oscillations in the posterior parietal cortex was negatively correlated with the amplitude of early evoked potential components there and positively correlated with response time. This finding implies that the greater the number of neurons recruited into this motor maintenance network prior to stimulus presentation, the fewer are available for sensory-motor processing following stimulus presentation.