The measurement of reinforcing brain stimulation

Abstract

Summary Rats with implanted monopolar electrodes in the lateral posterior hypothalamus were trained for self-stimulation behavior (ICSS). Thirty-eight different types of electrical stimulation were used as reinforcement for ICSS. It was assumed that one reinforcer was stronger than another if its effects on behavior were greater. The following types of behavior were then used to evaluate the strength of the reinforcing effect elicited by the 38 brain stimuli. (a) The bar-pressing rate on a continuous reinforcement schedule (rate method). (b) The amount of self-administered electrical charge as well as the percentage of time subjects (Ss) were stimulated (consummatory method). (c) The frequency with which a stimulus was chosen in a paired comparison procedure (choice method). (d) The voltage of foot shock necessary to suppress ICSS (cost method). The order of strength in which reinforcers were ranked under the different methods was estimated using the Spearman rank correlation method. The correlation coefficients were all positive, but they varied with the methods compared. This means that reinforcers were not ranked in the same order of strength by the different methods. A factorial analysis was performed, and it was shown that two factors were adequate to explain the differences observed between the methods. The hypothesis was then made that the reinforcing effect on behavior by brain stimulation in this brain area is a complex process comprising, at least, two factors.