Dexamethasone blocks sleep induced improvement of declarative memory.

To investigate the role of glucocorticoids for effects of early and late nocturnal sleep on declarative and procedural memory, 2 mg dexamethasone (versus placebo) were administered to healthy men 7 h prior to retention sleep. The retention sleep interval covered either the early or late half of nocturnal sleep. Following placebo, recall of a paired associate list (declarative memory) benefitted more from early than late sleep and recall of mirror tracing skills (procedural memory) benefitted more from late than early sleep. Dexamethasone did not affect slow wave sleep dominating early sleep, but blocked the beneficial effect of early sleep on recall of paired associates. Conversely, dexamethasone reduced rapid eye movement sleep dominating late sleep, but did not affect late sleeps beneficial effect on mirror tracing skills. The natural inhibition of endogenous glucocorticoid secretion during early sleep seems to be essential for a sleep-related facilitation of declarative memory.