Learned associations between drug states: Attempted analysis in Pavlovian terms

Abstract

A sedative dose of pentobarbital was injected into rats 30 min prior to a toxic dose of lithium on a number of occasions. A later test indicated that pentobarbital had lost its normal capacity to produce a mild aversion to previously consumed saccharin solution as a result of these pairings. This “avfail” (aversion failure) effect was opposite to predictions based upon principles of Pavlovian higher order conditioning. Attempts to implicate conditioned inhibition in avfail were unsuccessful, but led to discovery of another effect called conditioned sickness, which also resulted from pairing of pentobarbital with lithium: While the rats were sedated with pentobarbital, they avoided drinking novel saccharin solution. Conditioned sickness looked like straightforward Pavlovian conditioning until it was found not to be obtainable when other mild drugs were substituted for pentobarbital. Thus, neither avfail nor conditioned sickness was congruent with traditional Pavlovian principles of conditioning. Nevertheless, the avfail effect seems to involve learning because of its occurrence when a variety of drugs are substituted for pentobarbital or for lithium. Apparently, then, the learning involving association of feeling states, which probably has an important role in homeostasis, follows laws which are now undiscovered.