1. Monkeys were trained to 1) hold a handle in a central zone midway between "push" and "pull" while awaiting 2) an instruction telling them how to respond to a subsequent 3) perturbation, which triggered the instructed movement and was followed by 4) a reward if the movement was correct. 2. There were two sorts of instructions: push and pull. When the pull instruction had preceded the perturbation, the monkey responded to the perturbation by pulling, whereas after a push instruction, the monkey responded to the perturbation by pushing. 3. Recordings in pre- and postcentral sensorimotor cortex revealed instruction-induced changes of neuronal activity during the period intervening between the instruction and the perturbation-triggered movement. Effects of the instruction were differential depending on which of the two instructions was given, such differential responses to the instruction being detected in 61% of precentral pyramidal tract neurons (PTNs), 44% of precentral non-PTNs, and 11% of postcentral neurons. 4. Since motor cortex PTN axons end on alpha and gamma motoneurons and on interneurons of the spinal cord, changes of PTN activity with "intention" or "motor set" provide a mechanism for suprasegmental control and presetting of spinal cord reflex excitability specific to the nature of an impending movement.

Animals↗

PubMed1976

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

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.

Animals↗

PubMed1975

The Third Stevenson Lecture. Changing concepts of central control of movement.

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Animals↗