Abstract
Volitional limb motor control involves dynamic and static muscle actions. It remains elusive how such distinct actions are controlled in the central nervous system through separated or shared neural circuits. Here we explored the potential separation of neural circuitry for dynamic and static controls in the primate hand actions. We investigated the neuronal interactions between the spinal cord and forelimb muscles, and the motor cortex and the muscles, with an emphasis on their modulation during dynamic and static phase of grasping. While macaque monkeys were performing a precision grip comprising dynamic and static phases, we recorded spinal or cortical local field potentials simultaneously with electromyographic activity, thereafter examined neural coherence between the signals. We observed the emergence of beta-range neural coherence with muscle activity at spinal cord and motor cortex in the separated phases; spinal coherence during the grip phase and cortical coherence during the hold phase. Further, both of the coherence were influenced by bidirectional interactions with reasonable latencies as beta oscillatory cycles. These results indicate that dedicated feedback circuits comprising spinal and cortical structures underlie dynamic and static control of dexterous hand actions.