Effects of stress hormones on function and structure of the human brain

Animal studies by Rozendaal and McGaugh have established that glucocorticoids enhance memory consolidation but impair delayed memory retrieval. Our group has attempted to characterize this phenomenon in the human. We observed that cortisol treatment as well as psychosocial stress (Trier Social Stress Test) impairs delayed memory retrieval. In addition emotionally arousing material appears to be more impaired than neutral material. Finally, the testing condition also modulated the effects of cortisol on retrieval. In line with observations in rats we observed that cortisol impaired memory retrieval in a formal testing condition, while it had no impact on retrieval in a relatively relaxed non-formal testing condition. This last result supports the idea that a certain emotional arousal (probably leading to beta adrenergic activation in limbic regions) is a prerequisite for cortisol effects to occur. In contrast to these negative effects on retrieval we recently observed that cortisol treatment enhanced emotional memory consolidation, thereby further supporting the Model of Rozendaal and McGaugh. With respect to more chronic elevations of basal GC levels as occurring during aging or as a result of GC therapy we and others observed evidence for impaired memory. Whether or not these behavioural impairments are caused by structural changes in the hippocampus (hippocampal atrophy) remains a matter of debate. In sum cortisol elevations acutely have beneficial as well as detrimental effects on human memory. In the case of more chronic elevations the negative effects prevail, even though a substantial amount of functional and structural plasticity appears to remain.