The amygdala, specifically the basolateral region (BLA) is involved in the encoding of significant experiences and has been directly linked to memorable events. Extensive evidence suggests that stress hormones such as epinephrine play a critical role in consolidating new memories and this is why stressful memories are recalled vividly. Studies by Gold and van Buskirk provided initial evidence for this relationship when they showed that injections of epinephrine into subjects following a training period resulted in greater long-term retention of task related memories. This study also provided evidence that the level of epinephrine injected was related to the level of retention suggesting that the level of stress or emotionality of the memory plays a role on the level of retention. It is suggested that epinephrine affects memory consolidation by activating the amygdala and studies have shown that antagonism of beta-andrenoreceptors prior to injection of epinephrine will block the retention of memory effects seen previously. This is supported by the fact that beta-adrenoreceptor agonists have the opposite effect on the enhancement of memory consolidation. The BLA is thought to be actively involved in memory consolidation and is influenced strongly by stress hormones resulting in increased activation and as such increased memory retention. The BLA then projects to the hippocampus resulting in a strengthened memory. This relationship was studied by Packard and Chen who found that when glutamate was administered to the hippocampus, enhanced consolidation was seen during food-rewarded maze tasks. The opposite effect was also seen when the amygdala was inactivated using lidocaine. Studies appear to suggest that the amygdala effects the consolidation of memories through its influence with stress hormones and the projections to other brain areas implicated in memory consolidation.
