METHODS

Forty-five male squirrel monkeys (Saimiri sciureus), ranging in weight from 450 to 950 g, provided useful data. All experiments were performed on the left side. The animals were anesthetized with pentobarbital sodium (15 mg/kg); subsequent doses were given to maintain a moderate level of anesthesia. Temperature was maintained at 35-38 C. A circular bone flap was turned. The radius of the flap was 8 mm; its center was located 13 mm poste-rior to the junction of the frontal and parietal bones and 8 mm lateral to the midline. The cerebellum was exposed by removing the cerebral cortex posterior to the intraparietal sulcus with a combination of aspiration and blunt dissection. The ablation included the posterior parts of the left parietal and temporal cortex as well as the whole of the left occipital lobe. The cerebellar tentorium was incised and reflected. The anterolateral angle of the cerebellum-including portions of the ansiform lobe, the paraflocculus, and the flocculus-was ablated by gentle aspiration. This exposed the seventh and eighth cranial nerves for a distance of 1.5-2.0 mm, from their emergence in the internal auditory meatus to the edge of the brain stem (Fig. 1). The supe-rior branch of the vestibular nerve and, on most occasions, its inferior branch were visible. Two precautions were taken to immobilize