Drugs and memory: Evidence that drug effects can become associated with contextual cues by being paired post-trial with consolidation/re-consolidation. Mini review.

An extensive literature has validated the critical importance of a brief post-trial consolidation period for the incorporation of an experience into memory. Importantly, during this active consolidation state the memory formation is vulnerable to modification. While the subsequent stabilization of the memory makes it relatively resistant to modification, conditioned drug cues that re-activate the cue drug state association can initiate a re-consolidation process and during this re-consolidation the drug-cue association again becomes briefly unstable and sensitive to modification by post-trial treatments. Although most post-trial treatments shown to interact with memory consolidation processes have been used with instrumental learning protocols, this review is focused on recent findings that indicate that psycho-stimulant drug responses induced by apomorphine and morphine during the post-trial consolidation/re-consolidation state can become incorporated into the memory process. As a consequence, these post-trial drug treatment effects can be expressed in a subsequent non-drug test as behavioral responses comparable to the drug induced responses. In fact, apomorphine and morphine when administered post-trial can induce sensitization/conditioned effects that mirror the effects generated when these same drugs are administered in the presence of contextual cues. In addition, it has been shown that apomorphine given at stimulant/inhibitory dopaminergic dose levels post-trial during re-consolidation of a conditioned drug behavior can intensify/reverse the drug conditioning previously induced by apomorphine, morphine or haloperidol. The apparent efficacy of a post-trial drug state induced by a psycho-stimulant drug during consolidation/re-consolidation to become incorporated into contextual memory points up an alternative way, in addition to Pavlovian conditioning, by which psycho-stimulant drug effects can become embedded into an engram activated by contextual cues. These findings further suggest that drug treatments can be used to counter-condition the re-consolidated conditioned addictive drug response to substantially reduce the salience and motivational significance the conditioned association induced by the addictive drug.