Aging and the role of the HPA axis and rhythm in sleep and memory-consolidation.

Changes in the hypothalamo-pituitary-adrenal (HPA) axis and its rhythm with aging have interesting implications for sleep. Herein, the authors review sleep and HPA changes associated with normal aging and point out the similarities in how they change over time. The authors also discuss the effects of sleep on declarative memory consolidation, in particular. This focused review suggests that some of the declarative memory dysfunction with normal aging, and possibly procedural memory dysfunction, may be partially reversible by instituting methods to augment slow-wave sleep (SWS). Also, agents that decrease nocturnal corticotropin-releasing hormone and the cortisol nadir and enhance SWS may offer potential ways to manipulate the HPA axis/rhythm and improve sleep and memory. In this regard, the authors propose that drugs that act directly on the HPA axis (e.g., mineralocorticoid agonists) may be potentially quite useful for improving both sleep and declarative memory consolidation during sleep.