Dexamethasone blocks sleep induced improvement of declarative memory

To investigate the role of glucocorticoids for effects of early and late no cturnal sleep oil declarative and procedural memory, 2 mg dexamethasone (ve rsus placebo) were administered to healthy men 7 h prior to retention sleep . The retention sleep interval covered either the early or late half of noc turnal sleep. Following placebo, recall of a paired associate list (declara tive memory) benefitted more from early than late sleep and recall of mirro r tracing skills (procedural memory) benefitted more from late than early s leep. Dexamethasone did not affect slow wave sleep dominating early sleep, but blocked the beneficial effect of early sleep on recall of paired associ ates. Conversely, dexamethasone reduced rapid eye movement sleep dominating late sleep, but did not affect late sleeps beneficial effect on mirror tra cing skills. The natural inhibition of endogenous glucocorticoid secretion during early sleep seems to be essential for a sleep-related facilitation o f declarative memory. (C) 1999 Elsevier Science Ltd. All rights reserved.