Significance and Remembrance: The Role of Neuromodulatory Systems

It is now well known that the retention of newly-acquired information can be modulated by drugs or hormones administered shortly following training. It is generally thought that such treatments influence retention by modifying processes underlying the storage of information. The fact that susceptibility to posttraining memory modulation is seen in many species, including bees, fish, birds, and mammals, argues that some common time-dependent memory storage processes have been conserved in evolution. Recent research findings have provided strong support for the view that such susceptibility to posttraining influences provides opportunity for modulation of memory storage by endogenous neurohormonal systems. In rats and mice, posttraining administration of hormones such as epinephrine that are normally released by training experiences enhances subsequent retention. Comparable effects are found with posttraining administration of opiate receptor antagonists such as naloxone. Findings of recent experiments indicate that these treatments affect memory by influencing the release of norepinephrine within the amygdaloid complex. The endogenous regulation of memory storage appears to involve interaction of neurohormones and transmitters in activating brain systems involved in memory storage.