Approach‐avoidance analysis of rat diencephalon

Behavioral reinforcement by stimulation of diencephalic structures is by now well established. Delgado, Roberts, and Miller (’54), after the work of Hess (’54), Gastaut et al. ( ’ 5 2 ) , Kaada, (’51), and Masserman (’41, ’42) , established negative reinforcement to diencephalic stimulation in the region of the ventral posterior thalamic nuclei. Work of our own (Olds and Milner, ’54; Olds, ’56, ’60) has established positive reinforcement on stimulation in a system based in medial forebrain bundle regions of the lateral hypothalamus and also in the other brain regions tied together by the widely distributed medial forebrain bundle. Roberts (’58a, b), Brown and Cohen (’59), and Bower and Miller (’58) have indicated some regions where both approach and avoidance are evoked by stimulation of the same point. Brodie et al. (‘60) have shown, to the contrary, that some points yielding positive reinforcement in medial forebrain bundle regions of the macaque could not be made to yield any escape or avoidance reactions at all. Lilly (’58) has reported a focal point near the anterior commissure of the macaque where approach was produced by very low stimulation levels, and a point much lower (near the optic chiasma) where escape was produced by very low stimulation levels. In the rat, we (’60) have found points in medial forebrain bundle regions where stimulation produced positive reinforcement only, points in dorsomedial tegmentum where stimulation produced negative reinforcement only, and points in between these two types, where stimulation produced both positive and negative reinforcement. Questions remain unanswered concerning the pervasiveness of the areas of pure positive reinforcement, of pure negative reinforcement, and of overlap. More specifically, the questions are concerned with which areas are involved in each phenomenon. The present study takes up these questions with respect to diencephalic centers and some bordering regions of midbrain and telencephalon in the rat.