Impaired declarative memory consolidation during sleep in patients with primary insomnia: Influence of sleep architecture and nocturnal cortisol release.

BACKGROUND: A central cognitive function of sleep is to consolidate newly acquired memories for long-term storage. Here, we investigated whether the overnight consolidation of declarative memory in patients with chronic sleep disturbances is impaired, owing to less slow wave sleep (SWS) and an increased cortisol release.

METHODS: Polysomnographic recordings, serum cortisol concentrations, and overnight memory consolidation in 16 patients with primary insomnia were compared with those of 13 healthy control subjects.

RESULTS: Patients displayed distinctly less overnight consolidation of declarative memory (p < .05), which was significantly correlated with SWS in the control subjects (r = .69) but with rapid eye movement (REM) sleep in the patients (r = .56), who had a diminished amount of SWS (p < .05). Increased cortisol levels in the middle of the night were associated with impaired retrieval of declarative memory after sleep for both control subjects (r = -.52) and patients (r = -.46).

CONCLUSIONS: Primary insomnia is associated with a diminished sleep-related consolidation of declarative memory. Efficient overnight consolidation of declarative memory is associated with high amounts of SWS and low serum cortisol levels during the early part of the night. Where SWS is decreased, REM sleep might play a partly compensatory role in the consolidation of declarative memory.