THE INFLUENCE OF POSTURE ON RESPONSES ELICITABLE FROM THE CORTEX CEREBRI OF CATS

Abstract

Points on the ant. sigmoid gyrus of 22 unanesthetized cats were stimulated through permanent electrodes over a period of several weeks. The experiments demonstrate that stimulation of these points with a weak (non-convulsive) 60 cycle sine wave current caused the extremity responding to the stimulus to take a definite position rather than the elicitation of any certain movement. Predictable movements could be elicited from fixed points, however, by controlling the initial position of the responding leg. Latencies of the responses were altered (shortened) by increasing the distance of the initial position of the extremity from the elicited ("final") position. This relationship was lost in the animals whose responding extremity had been deafferented. Latencies of the responses elicited with currents of fixed strength were found to vary over wide ranges (several seconds) dependent on the level of excitement of the animal when stimulated. The tonic neck reflexes were demonstrated to exert an influence on the final position. These reflexes also appeared to affect the latency of the responses when other variables affecting this interval were controlled. The results demonstrate that the activities of at least certain postural reflexes are coordinated with the impulses arising in the electrically excited motor cortex, and that posture is a variable that must be considered in a complete analysis of the responses obtained from the motor cortex of unanesthetized or lightly anesthetized animals.