Historical context of state dependent learning and discriminative drug effects.

Drug-induced state dependent learning (SDL), as well as similar effects on memory retrieval exercised by physiological states, have been known since 1830. Before 1950, understanding of this area derived primarily from clinical descriptions of somnambulism, dream recall, fugue states, and cases of multiple personality. After 1950, experimental demonstrations of the properties of SDL and drug discriminations (DDs), along with a series of changes in the DD procedure, have led to the DD paradigm that is currently employed, and which has properties that make it an extremely useful tool for preclinical investigation of a variety of pharmacological and psychological questions. These conceptual and technical developments have resulted in widespread acceptance of the DD paradigm as a preclinical research method. This paper reviews the nineteeth and twentieth century history of clinical observations, concepts, and experiments, that have led to our current status of knowledge about drug discriminations and SDL.