Observational determination of dose-response curves in hallucinogen-treated monkeys.

An objective behavioral profile that was previously shown to distinguish the effects of hallucinogens from those of other classes of drugs was used here to further study hallucinogenic behaviors. Saline, d-amphetamine sulfate and five doses of dimethyltryptamine (DMT) were administered to solitary adolescent rhesus monkeys in a totally dark environment and their behavior was observed via infrared monitors, videotaped, and scored in a number of categories. Scores in the following categories systematically increased with ascending doses of DMT; exploration, locomotion, stereotypy, spasm, tracking and duration of inappropriate behavior. In addition, some behaviors sensitive to hallucinogens occurred with greater frequency in the dark than in a previous study conducted in the light. Behaviors such as tracking and fear grimaces, usually associated with specific stimuli, emerged in the absence of such stimuli in the dark. These results suggested hallucinogen-induced changes in perceptual-motor systems, if not hallucinations per se.