Elsevier

Brain Research

Volume 71, Issues 2–3, 17 May 1974, Pages 479-494
Brain Research

Gating of motor cortex reflexes by prior instruction

https://doi.org/10.1016/0006-8993(74)90992-5Get rights and content

Abstract

A previous study showed that sensory input can generate reflex motor cortex output in association with learned movement when the sensory input has a strong connection to the motor cortex, e.g., when a stimulus calling for repositioning of the hand consists of a perturbation of hand position. The present study has shown that motor cortex reflexes can be ‘gated’ on or off by the voluntary ‘set’ of the monkey. A monkey was trained to grasp a handle and maintain it in a certain position for 2–4 sec; he was then given an ‘instruction’ as to how he should respond to a forthcoming perturbation of the handle. The ‘instruction’ was a red or green light which appeared between 0.6 and 1.2 sec prior to the handle perturbation. The red light signaled that the monkey should pull toward himself when the perturbation occurred, and the green light meant that he should push away when the perturbation occurred. Two different sorts of perturbation were used, one being a movement of the handle toward the monkey and the other away from the monkey. A given instruction called for a movement synergistic with segmental stretch reflexes for one of the perturbations and antagonistic to these reflexes for the other. Following training, activity of motor cortex neurons was recorded during task performance. Neurons in precentral motor cortex showed changes of activity according to the ‘instruction’ as early as 200 msec following the onset of red or green light. In addition, the short (20 msec) latency motor cortex response evoked by the subsequent perturbing stimuli differed markedly depending upon the prior instruction. The finding that the set and expectancy of the monkey could profoundly modify this ‘reflex’ response indicates that the transcortical serov-loop proposed by Phillips is subject to powerful modulation as a function of learning and volition.

Résumé

Uneétude antérieure avait montréqu'un message sensoriel peut induire une réponse réflexe du cortex moteur en association avec un mouvement appris lorsque le message sensoriel présente une connexion puissante avec le cortex moteur, par exemple lorsqu'un stimulus qui inciteàrepositionner la main consiste en une perturbation de la position de la main. L'étude actuelle a montréque les réflexes du cortex moteur peuventeˆtre mis en circuit ou hors circuit selon le type d'activitévolontaire du singe. Un singe aétéentraînéàsaisir une poignée etàla maintenir dans une certaine position pendant 2–4 sec; il re¸oit alors une ‘instruction’ sur la manière dont il devrait répondreàla prochaine perturbation de la poignée. L'instruction a l'aspect d'une lumière rouge ou verte qui apparaît de 0,6–1,2 sec avant la perturbation de la poignée. La lumière rouge signale que le singe devrait tirer la poignée vers lui lorsque la perturbation survient et la lumière verte signifie qu'il devrait pousser la poignée pour l'écarter de lui lorsque la perturbation se produit. Deux types différents de perturbations sont utilisés: l'une consiste en un mouvement du levier vers le singe et l'autre en un mouvement en sens opposé. Pour une instruction donnée, le mouvement suscitéest synergique aux réflexes d'étirement segmentaires dans un type de perturbation et antagoniste aux meˆmes réflexes dans l'autre type. Après entraînement de l'animal, l'activitédes neurones du cortex moteur aétédérivée pendant l'exécution de la taˆche. Les neurones du cortex moteur précentral ont montrédes changements d'activitéen fonction de l'‘instruction’; des délais aussi précoce que 200 msec après le début de la lumière rouge ou verte ontétéobservés. De plus, les réponsesàlatence courte (20 msec) du cortex moteur induites par le stimulus perturbateur qui succède diffèrent considérablement selon l'instruction préalable. L'observation selon laquelle le type de mouvement et l'attente du singe peuvent modifier profondément cette réponse ‘réflexe’ indique que la boucle d'asservissement transcorticale proposée par Phillips est sujetteàune modulation puissante en fonction de l'apprentissage et de la commande volontaire.

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