Electrical Stimulation of the Shark Brain

Abstract

synopsis. Early studies using various means to electrically activate portions of the brain in immobilized elasmobranchs are critically reviewed. The results of brain stimulation experiments using modern techniques are then considered in light of this background material. Preliminary experiments on anesthetized-immobilized sharpnose and bonnethead sharks are given as an outline of the types of responses that can be studied using acute preparations of pelagic sharks. The responses evoked can be grouped into the following categories: arousal and swimming; body, fin and eye movements suggestive of circling and loss of equilibrium; possible components of agonistic and reproductive behavior; head, mouth and respiratory movements and possible color changes. Chronic studies on free-swimming sharpnose sharks are discussed with respect to potential areas for future study. Responses suggestive of portions of agonistic and feeding behavior were evoked but no attempt was made to localize the areas stimulated. The behavioral effects of electrical stimulation of 85 electrodes in free-swimming juvenile nurse sharks are pre? sented in some detail. The anatomical distribution of sites from which the following responses have been elicited are plotted on representative sections of the brain: arousalescape; coughing; head shaking; barbel movement; eye retraction; biting or mouthing food; snapping up gravel; slow dragging of the barbels across the substrate; circling; rolling about the long axis; continuous swimming and interrupted swimming. Several possible functional-anatomical systems are suggested to account for some of these results.