THE RESPONSES TO CHANGES IN ENVIRONMENTAL TEMPERATURE AFTER REMOVAL OF PORTIONS OF THE FOREBRAIN

Abstract

The observations reported were made on dogs and cats which survived the removal of portions of the forebrain for long periods (6 wks. to 28 mos.). After removal of the neopallium and part of the hippocampus, including the fornix, with subsequent secondary degeneration of large portions of the dorsal thalamus, the dogs showed functional changes in their temp.-control mechanisms: (1) chronic vasodilatation, with failure of the skin vessels to constrict normally to cold; (2) absence of true polypneic panting; (3) a very delayed slow type of hyperpnea in response to conditions that promptly induced a true panting in the same animals before operation; (4) a rise in rectal temp. before hyperpnea developed; (5) immediate and vigorous shivering in response to cold, frequently producing a rise in body temp., whereas before operation the same animals showed the usual delayed and less marked reaction with a fall in body temp. The cats with equivalent lesions behaved similarly to cold, but the responses were subject to wider variations than those of the dogs. No differences in temp. control were noted between these animals and others with more extensive lesions, which left only the hypo-thalamus intact, together with the contiguous portions of the medial basal olfactory areas and of the caudal pole of the dorsal thalamus. All these animals maintained normal body temps. under ordinary conditions and withstood exposure to heat (37.5-41.4[degree]C) and cold (0.6-15[degree]C) for long periods (45 min. to 4 hrs.) with relatively small changes. Observations on animals with unilateral lesions and with ablations of limited portions of the cortex suggest that the cortical control of the vasomotor responses to temp. changes is localized in the contralateral motor-sensory area.