Effects of food deprivation on free-operant avoidance behavior

Lever pressing was maintained by Sidman's shock-postponement procedure and Herrnstein and Hineline's shock-frequency-reduction procedure with rats. Food deprivation to 80% and 70% of the animals' body weights on free feeding resulted in decreased response rates in both avoidance paradigms tested. Reinstatement of free-feeding conditions increased body weights and response rates and decreased shock rates. The effects of food deprivation were not dependent upon any particular avoidance parameters, or types, intensities, or durations of electric shock. These results mean that weight control is essential in long-term studies of avoidance behavior, and in studies of the effects on avoidance behavior of physiological interventions, such as hypothalamic lesions, that themselves may produce weight changes.     

Effects of food deprivation and reinforcement magnitude on conditioned suppression

In Experiment I, the responding of rats lever pressing on a variable-interval schedule for sucrose solution was partially suppressed by a variable duration conditioned stimulus followed by shock. When food deprivation was increased, response rates during and before the conditioned stimulus increased monotonically. Varying the concentration of sucrose across blocks of sessions or from session to session in a semi-random sequence had little effect on response rates either before or during the conditioned stimulus. With a fixed sequence of increasing concentrations across a five-session block, increased concentration produced much more rapid increases in response rates before than during the conditioned stimulus. In Experiment II, rats were presented with the same sequence of increasing concentrations across a five-session block. When tested at 80% body weight, response rates increased rapidly as concentration increased, but at 100%, body-weight rates increased only slightly. The effect of a change in body weight in Experiment II thus mimicked the effect of the conditioned stimulus in the latter part of Experiment I. These findings support the view that the effect of a pre-aversive conditioned stimulus is similar to that of a change in food deprivation, but unlike that of a change in reinforcement magnitude.