Adrenal Stress Hormones and Enhanced Memory for Emotionally Arousing Experiences

Abstract

Emotionally significant experiences tend to be well remembered., We know this from personal experiences as well as from extensive research findings. Significant experiences such as birthdays, graduation ceremonies, or the loss of a loved one typically leave lasting and vivid memories. Findings of experimental studies indicate that people have good recollections of where they were and what they were doing when they experienced earthquakes or witnessed accidents. Similarly, a rat remembers the place in an apparatus where it received a footshock or the location of an escape platform in a tank filled with water., Such memory enhancement is not limited to experiences that are unpleasant or aversive. Pleasurable events also tend to be well remembered. Our research focuses on understanding the role of emotional responses induced by such arousing experiences in enabling the significance of events to regulate their remembrance.Extensive evidence indicates that stress hormones released from the adrenal glands are critically involved in memory consolidation of emotionally arousing experiences. Epinephrine, glucocorticoids, and specific agonists for their receptors administered after exposure to emotionally arousing experiences enhance the consolidation of long-term memories of these experiences.Do stress hormones also enhance memories of experiences that are not emotionally arousing? The findings of recent experiments suggest that this may not be the case. As discussed below, we recently reported that the endogenous glucocorticoid corticosterone enhanced memory consolidation of object recognition training when administered to rats that were emotionally aroused by an unfamiliar training apparatus. However, the treatment had no effect when administered to rats that had extensive prior habituation to the training context in order to reduce novelty-induced arousal. In studies of human memory, epinephrine or cortisol treatment also appear to selectively enhance memory for emotionally arousing material.These findings thus provide some important clues concerning the neurobiological mechanism(s) underlying adrenal hormone effects on memory consolidation and suggest that at least some degree of training-associated endogenous emotional arousal is essential for enabling their effects on memory consolidation. Our findings indicate that adrenal stress hormones influence memory consolidation of emotional experiences via interactions with arousal-induced activation of noradrenergic mechanisms within the amygdala.