Expectation of rewards and emotional behavior in monkeys

Abstract

From previous theoretical proposals about emotional processes, it was hypothesized that the lack of, or delay of, expected reinforcement for a previously rewarded ongoing plan of action would be associated with emotional behavior. This hypothesis was confirmed by altering the reward contingencies during the differential reinforcement of low rates (DRL) schedule. The DRL requires that the animal wait for a prescribed time interval before responding in order to be reinforced; premature responses are non-rewarded and postpone the availability of a reward until the next prescribed time interval has elapsed. Using each monkey as his own control, two experimental approaches were employed; a mid-point change in the length of the DRL interval or availability of rewards, and discrete manipulations of reward contingencies (no reward or extra rewards) for approriately timed delayed responses after a train of prior consecutive rewards had been established. For the mid-point change experiment, lengthening the DRL interval was associated with sustained emotional behavior, such as bursts of responding and vigorous activity. For the discrete reward manipulations, the lack of expected reinforcement for delayed timing responses that ordinarily would have been rewarded was associated with emotional behavior. The DRL schedule is useful for studying emotional behavior associated with the lack of or delay of rewards. This approach may complement experimental paradigms for studying emotion in animals that employ the use of noxious or painful stimuli. The lack of expected rewards may provide a relevant model for investigating certain types of emotions, such as frustration and anger.