Control of Posture by Reticular Formation and Cerebellum in the Intact, Anesthetized and Unanesthetized and in the Decerebrated Cat

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Abstract
In this study of the medullary reticular formation,the predominant effect on postural tonus was reciprocal. Direct stimulation of the medial reticular formation yielded a postural pattern of ipsilateral flexion, extensor inhibition, and contralateral extension and flexor inhibition. The lateral reticular formation evoked a pattern opposite in direction to the medial one. Both patterns were followed by poststimulatory "cerebellar-type" rebound effects opposite in direction to those evoked by stimulation. Indirect reticular activation from the cerebellum also gave 2 postural patterns and rebounds: one, related to the vermal cortex and to the fastigial nuclei, was identical to that evoked from the medial reticular pattern (and from the restiform body); the other, obtained from the lateral cortex of anterior lobe and paramedial lobule and from the interpositus nuclei, was similar to that from the lateral reticular formation (and from the brachium conjunctivum). The reticular patterns persisted unchanged after acute removal of the cerebellum, but the poststimulatory rebound reversal was lacking after chronic cerebellectomy had allowed complete degeneration of the cerebellobulbar tracts. Stimulation of the medullary reticular formation through chronically implanted electrodes revealed in the unanesthetized, freely-moving animal a number of well organized movements of the whole body. The entire postural substratum of sleep was produced from one medial reticular point. Generalized nonreciprocal inhibition and facilitation commonly ascribed to the medial and lateral reticular areas were never found in the intact unanesthetized animal. They were much less frequent than were the reciprocal postural patterns in the decerebrate animal, and were in most cases obtained at stimulus intensities 2-3 times threshold strength, the threshold response having been reciprocal. It is concluded that the concept of generalized, diffuse, nonreciprocal "inhibitory" and "facilitatory" functions of the reticular formation is valid only within rather limited experimental conditions and cannot be used to explain the mechanism of the management of posture, including that of the decerebrate animal. The over-all evidence indicates that the bulboreticular formation, as well as the cerebellum, evokes inhibitory and facilitatory influences on postural tone in a reciprocal manner.

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