On the nature of directed behavior to drug-associated light cues in rhesus monkeys (Macaca mulatta).

Abstract

The present study investigated the role of drug-paired stimuli in controlling the behavior of rhesus monkeys. Systematic observations were made with nine monkeys who had a history of drug self-administration; they had been lever pressing to produce intravenous infusions of various drugs. These observations revealed that the stimulus light co-occurring with drug infusion produced robust and cue-directed behavior such as orienting, touching and biting. Experiment 1 showed that this light-directed behavior would occur in naïve monkeys exposed to a Pavlovian pairing procedure. Four monkeys were given response-independent injections of cocaine. In two monkeys, a red light preceded cocaine injections by 5 s, and a green light co-occurred with the 5-s cocaine injections. In the other two monkeys, the light presentations and cocaine injections occurred independently. Light-directed behavior occurred in all four monkeys within the first couple of trials and at high levels but decreased across sessions. The cocaine-paired stimulus maintained behavior longer and at higher levels than the uncorrelated stimuli. Furthermore, light-directed behavior was not maintained when cocaine was replaced with saline. Light-directed behavior did not occur in the absence of the lights. When these monkeys were subsequently trained to lever press for cocaine, light-directed behavior increased to levels higher than previously observed. Behavior directed towards drug-paired stimuli is robust, reliable and multiply determined; the mechanisms underlying this activity likely include Pavlovian conditioning, stimulus novelty, habituation and operant conditioning.

The discipline of behavioral pharmacology.

“…Perhaps for that reason, save for situations where drugs are described as discriminative stimuli, reinforcing stimuli, or, less often, motivating operations, contemporary researchers rarely attempt to isolate or to describe behavioral mechanisms of drug action. The contribution of Reilly, Berndt, and Woods (2016) to this issue clearly demonstrates how behavioral mechanisms of drug action, even if complex, can be isolated. It also illustrates the explanatory value of such an approach, which, in our opinion, should be adopted far more often that currently occurs.…”