Effects of olanzapine on slow wave sleep, sleep spindles and sleep-related memory consolidation in schizophrenia

Introduction: Memory deficits and sleep disturbances are common clinical features of schizophrenia. Sleep is supposed to promote memory consolidation and the antipsychotic olanzapine is suggested to improve both sleep and memory functions. Therefore we performed a study to analyse the acute effects of olanzapine on distinct sleep parameters and sleep-related memory consolidation in parallel. Methods: We studied 26 patients with schizophrenia on stable antipsychotic medication with amisulpride (age range 19-44 years). Immediately before polysomnography and the morning after we performed neuropsychological tasks. Before the third night in the sleep laboratory, patients received either olanzapine or a placebo. Results: We found a significant positive association for slow wave sleep and declarative memory performance in schizophrenia at baseline. Additionally, Stage 2 sleep spindle density was positively related to overnight memory consolidation. Olanzapine caused a significant increase in the amount of slow wave sleep in accordance with recent studies, but led also to a significant decrease in sleep spindle density, which had not been described before. Memory performance the next morning was not different between the two groups. Discussion: Since not only slow wave sleep but also sleep spindles are supposed to promote sleep-related memory consolidation, we suggest that a putative positive effect on memory performance by slow wave sleep augmentation is neutralised by the decrease in sleep spindles due to olanzapine.