Visual declarative memory is associated with non-rapid eye movement sleep and sleep cycles in patients with chronic non-restorative sleep

Abstract

Objective Sleep contributes to processes of memory, but many questions still remain open. The aim of this study was to test the role of different aspects of sleep for memory performance in a group of patients with chronic non-restorative sleep. Methods Forty-two consecutive patients (mean age 40.3 years; 31 women) with non-restorative sleep were included. All subjects underwent polysomnography for diagnostic reasons and obtained the following diagnoses (International Classification of Sleep Disorders, ICSD): psychophysiological or idiopathic insomnia ( N = 18), paradoxical insomnia ( N = 13), mild hypersomnia ( N = 6), and dysthymic disorder ( N = 5). Patients with sleep-related breathing disorders or restless legs were not included. Prior to polysomnography on the second night and the next morning, neuropsychological tests were performed. Declarative memory was tested by the Rey–Osterrieth Complex Figure Test and a paired associative word list. Procedural learning was assessed by a mirror-tracing skill. Results Visual declarative memory performance was significantly associated with total sleep time, sleep efficiency, duration of non-rapid eye movement (NREM) sleep and number of NREM–REM sleep cycles, but not with specific measures of REM sleep or slow wave sleep. Conclusions Further indications of a role of sleep, and in particular of NREM sleep and sleep organization, for visual declarative memory were found.