EFFECT OF ACUTE BRAIN STEM LESIONS ON THE ELECTRICAL ACTIVITIES OF THE LIMBIC SYSTEM AND NEOCORTEX

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Abstract
The effects of acute brain stem lesions upon the electrical activity of the neo-, paleo-, and archicortical systems were observed in unanesthetized curarized cats under artificial respiration, and the following results were obtained. In the cerveau isole preparation, the paleo-, and archicortices often showed a continuous arousal pattern, while a sleep pattern with spindle bursts was recorded in the neocortex. The activation threshold for the paleo-, and archicortices by hypothalamic stimulation was not altered, while the threshold for the neocortex was considerably elevated. The activation threshold for the neocortex following medial thalamic stimulation was not changed. Lesions of the posterior part of the hypothalamus produced the deep sleep pattern both in the neocortex and limbic system. The neocortex was easily activated by sciatic nerve stimulation, while the activation threshold for the paleo-, and archicortices was considerably elevated, and hippocampal arousal waves appeared only often strong stimulation of the remaining activating structures. It was suggested that the influence of the posterior hypothalamus upon the electrical activity of the neocortex was exerted not directly from the hypothalamus to the neocortex, but via the reticular formation. After the lesion of the preoptic region, the electrical activity level of the neocortex showed less change, while the activity levels of the paleo-, and archicortices were remarkably lowered and the activation of these cortices was very difficult. Massive destruction of the medial part of the thalamus produced continuous slow waves in the neocortex, while changes in the patterns of the paleo-, and archicortices was not so remarkable. These findings seem to confirm the existence of the hypothalamic activating system on the paleo-, and archicortices, which is relatively independent of the reticular activating system in the strict sense.

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