The neural and chemical basis of reward: New discoveries and theories in brain control of feeding, mating, aggression, self-stimulation and self-injection

Abstract

Discovery of endogenous opiates raises the possibility that they serve as a reward for behavior, including law-abiding behavior. This paper begins with a discussion of homeostatic behavior, drinking, feeding, and then social behavior, mating and aggression. It is possible that peptide fragments of longer protein chains serve as ‘drive peptides’ in the sense that each is evolutionarily adapted to serve a battery of body and brain functions. Dual function, gut-brain peptides have recently been discovered for digestion and satiety, blood volume and thirst, and ovulation and sexuality. Aggression-control peptides are a logical possibility. Studies are described in which feeding, mating and killing responses are induced or blocked by electrical or chemical stimulation of the hypothalamus in the rat. Animals will also work to stimulate their own brain electrically or with the catecholaminergic drug, amphetamine, or with the opiates morphine and enkephalin. These reward systems could conceivably reward not only homeostatic behavior and self-centered social behavior, but also altruistic behavior. A hypothetical model of brain function is proposed in which endogenous catecholamine and/or opiate rewards are released by behavior that matches a memory or ‘rule’ of prior behavior. Thus complying with internalized laws or expectations is in itself rewarding. Altruism as such is not necessarily innately rewarding, but matching performance to expectation probably is. Behavioristic, physiological psychology can explore the role of opiates in legal expectations; behavioristic cultural anthropology can explore the legal expectations that people depend on for their reward. In summary, a theory is presented in which innately coded peptides prime physiological and behavioral patterns for feeding, mating and aggression; catecholamines modulate arousal and activation; and opiates reward successful compliance with rules, most of which are learned, some of which are laws.