AVERSIVELY MOTIVATED CHANGES IN MEAL PATTERNS OF RATS IN A CLOSED ECONOMY - THE EFFECTS OF SHOCK DENSITY

Rats lived continuously in an operant chamber in which they were able to press a bar to obtain food on a chained FR50:CRF schedule that allo wed them control of both the size and frequency of individual meals. I ndependent groups of animals were scheduled to receive 12, 24, 48, or 96 electric shocks per day, which were given randomly in time and inde pendent of the subjects' behavior. Rats could avoid shock by remaining in a safe area of the chamber, but they were always at risk while bar pressing. The introduction of shock resulted in a number of changes in feeding patterns. In rats exposed to a possible 12 shocks/day, meal s ize increased whereas meal frequency changed very little. At 24 shocks /day, meal frequency decreased whereas meal size increased such that n et intake remained stable relative to a preshock baseline period. As s hock density was increased to 48 or 96 shocks/day, total intake was su ppressed. At 96 shocks/day, both meal frequency and meal size decrease d dramatically. Shock-related changes were also observed in rates of o perant responding and in the amount of time the animals engaged in fee ding-related behavior. All of the animals were able to achieve a great er than 50 % reduction in the total number of shocks received relative to equivalent random samples of their position in the apparatus taken during baseline. These results support the position that the nature o f defensive changes in feeding behavior that are seen when an aversive stimulus is introduced into a simulated foraging situation varies as a function of risk.