Reflex and intended responses in motor cortex pyramidal tract neurons of monkey

TLDR

Monkeys were trained to react to an arm perturbation according to a prior instruction, learning to respond appropriately to push or pull cues regardless of perturbation direction. Pyramidal tract neurons in contralateral motor cortex arm area exhibited two dissociable responses to perturbation: a 20–25 ms reflex component tied to perturbation direction and a 40–50 ms intended component tied to the preceding instruction. Intended PTN discharge can occur as early as 50 ms after perturbation, even when the initial reflex effect is inhibitory, and these short‑latency intended responses are faster than those evoked by auditory or visual cues, suggesting a role in volitionally controlled limb movements. No additional metadata.

Abstract

1. Monkeys were trained to react to an arm perturbation according to an instruction delivered prior to the perturbation. There were two possible instructions (push or pull), and monkeys learned to respond accordingly regardless of the direction (push or pull) of the triggering perturbation. 2. Pyramidal tract neurons (PTNs) in contralateral motor cortex arm area responded to the triggering perturbation with two dissociable components: 1) a relatively short-latency (20-25 ms) reflex component which depended on the direction of the perturbation, and 2) a longer latency (40-50 ms) intended component which depended on the prior instruction. 3. Intended PTN discharge could occur in arm area with latencies of 50 ms even following arm perturbations whose initial reflex effects on the PTN were inhibitory. 4. Intended PTN responses triggered by perturbations of the appropriate body part occur at shorter latencies than intended PTN responses triggered by auditory or visual stimuli. These short-latency intended PTN responses may play a role in thsshort-latency but volitionally controlled limb movements occurring in response to limb perturbations.