Activity-induced reward and related phenomena

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My interest in the motivational/rewarding effects of exercise stems from studies of activity anorexia in rats, an animal model of anorexia nervosa in humans. To produce activity anorexia, rats are allowed limited daily access to food (e.g., 60 min). The rest of the day these rats have access to running wheels. The rats run in the wheels and lose weight; the more weight they lose, the more they run. Some rats run as much as 20 km a day. Moreover, they do not eat enough during their daily meal to compensate for the energy expended in running, so, if the process is allowed to continue, death ensues. Even more amazing is the fact that running suppresses eating. These rats eat less during their daily meal than other rats that are similarly food deprived, but not allowed to run.      Dr. B. T. Lett and I started a research program based on the hypothesis that the excessive wheel running and its effects on eating involve activation of a reward system in the brain - perhaps the same system as that activated by addictive drugs such as morphine or amphetamine. The main objective of the proposed research program is to arrive at a better understanding of the motivational and rewarding effects of exercise. In turn, this should contribute to a greater understanding of the behavioral and neural mechanisms of reward and motivation.      At least two applications of the work are of general significance: 1. Activity anorexia in rats is considered an animal model of anorexia nervosa in humans, so any information about the causes and mechanisms of the phenomenon in rats may have practical implications for understanding and treating the disorder in humans. 2. The view that certain nondrug rewarding activities, like exercise, are addictive is becoming more accepted. Thus our research on wheel-running exercise in rats may have implications for exercise addiction, and, more generally, for addictions to other nondrug rewarding activities (gambling, eating, etc.)