Rate of Recovery of Functioning in Cats with Rostral Reticular Lesions

Recent studies, experimental and clinical, emphasize that damage to the rostral brain stem leads to derangement of consciousness, the site of emphasis being the mesial tegmentum of the midbrain. Earlier Bremer 2 stressed the similarity between sleeping cats and those with cerveau isol~ (midbrain transection) and attributed the former to interruption of the tonic drive propagated rostrally over the great afferent paths. The cerveau isol~ preparation also showed the spontaneous spindling of the sleep electroencephalogram . Lindsley, Bowden and Magoun s added selective sections of the lemniscus to enc~phale isol5 (acute C1 transection) preparations. This did not convert the activation tracing characteristic of the enc~phale isol5 to the cerveau isol~ type. However, lesions that instead destroyed sub- and hypothalamus from optic chiasm to mammillary bodies or anterior midbrain did produce a sleep tracing. Additionally, Lindsley et al2 studied the effects of chronic lesions. In animals with lesions in the ponto-midbrain tegmentum, midbrain tegmentum, hypothalamus, and junction between hypothalamus and thalamus, the common behavioral result (variable in degree depending upon site and extent of the lesion) was a postoperative somnolence or lethargy in which the animal displayed little or no spontaneous activity of a purposive sort, and seemed unaware of ordinary environmental stimuli. The animal with a midbrain tegmental lesion blocking much or all of the rostral end of the reticular activating system lay on its side with eyes closed as if deeply asleep during its ~l-day survival period. By contrast, in ~ anireals in which the periaqueductal gray was injured an approximation of normal sleeping-waking behavior was regained. Two others, with lateral mesencephalic lesions which spared the mesial tegmentum, became able to stand and walk again and showed activation of the electroencephalo graphic tracing. Experiments on 9 monkeys reported by French and Magoun 6 appeared generally to confirm these results so far as destruction of the reticular activating system and the associated behavioral deficits are concerned.