Recall rendered dependent on an opiate state.

Remembering may require that the organism be in a state that is similar to that in which the event was initially experienced (state dependence [StD]). We determined whether morphine induces StD and whether this StD is conceivably involved in the analgesic effects that opiates produce. Rats trained while treated with morphine recalled the learned response when tested with this opiate but not when in their nondrugged state, and vice versa. Furthermore, morphine analgesia occurred in a manner that was similar to StD in terms of both dose and time. In as much as responses to nociceptive stimulation are learned during the course of ontogeny, StD may constitute the psychophysiological mechanism whereby opiates produce their characteristic analgesic effects.