REGULATION OF POSTURE IN INTACT AND DECEREBRATE CAT: I. CEREBELLUM, RETICULAR FORMATION, VESTIBULAR NUCLEI

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Abstract
Selective, unilateral ablation of the medial cortex of the anterior lobe of the cerebellum in the cat decerebrated above or below the pons (also in the intact animal), results in a posture of ipsilateral extension and contralateral flexion of the limbs. Subsequent destruction of the ipsilateral fastigial nucleus completely reverses the cortical posture. Thus cortex and its nucleus of projection exert opposite influences on postural tonus. The fastigial nucleus, in addition to relaying cortical activity, has an important extracortical function. Unilateral destruction of Deiter''s vestibular nucleus results, in the decerebrated cat, in ipsilateral flexion and in contralateral extension of the limbs, similar to that following fastigial lesion. Bilateral destruction of Deiter''s nuclei in the decerebrated animal gives an appreciable reduction, but not in abolition, of extensor rigidity. Decerebrate rigidity is not dependent on the integrity of the vestibular nuclei. Decerebrate rigidity is abolished by combined destruction of fastigial and Deiter''s nuclei, leaving the pontobulbar reticular formation intact. This part of the reticular formation, as far as postural tonus is concerned, is not intrinsically active, but is dependent on activation from other sources. Decerebrate rigidity is not abolished by brain stem transection, at least as far caudal as the rostral part of the trapezoid body, providing neither fastigial nor Deiter''s nuclei is injured. The evidence cited above shows conclusively that only a small part of the brain stem reticular formation is sufficient to maintain decerebrate rigidity, providing that this part is activated from certain sources. Important among these are the fastigial and vestibular nuclei. New explanations are offered on the basis of these observations for the dual function (stimulation and rebound) of the cerebellum on postural tonus, and for the mechanism of decerebrate rigidity.
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