New Considerations in the Neuropsychology of Motivated Behaviors

Abstract

Psychologists often distinguish between separate classes of behaviors, which appear to be under different complexities of neural control. Simpler behaviors, such as the leg-flexion reflex of the spinal dog, appear to depend primarily on the initiating stimulus, and are not modified by their outcome (Sherrington, 1906). In contrast, most of the behaviors of interest to psychopharmacologists, such as eating, aggression, and escape from danger, are motivated acts. They are dependent on the outcome they produce, so that the success or failure of prior experiences determines the intensity and persistence of the behavior. For instance, a hungry rat pressing a bar for food reward will soon cease if food is withheld. By using the performance of such an instrumental task as a criterion, it has been shown that rats are motivated not only to eat, drink, and avoid pain, but also to engage in a wide variety of regulatory and instinctive acts (e.g., copulation—Sheffield et al., 1951; mouse-killing—Myer and White, 1965; regulation of body temperature—Weiss and Laties, 1961). Behavioral theorists often model the complexity of motivated behavior by postulating “central motive states” (i.e., hunger, thirst, aggressiveness), the strength of which is thought to be determined by internal (e.g., nutrient availability) as well as external (e.g., food-odor) stimuli.