Sleep-related memory consolidation in the psychosis spectrum phenotype

Sleep and memory processing impairments range from mild to severe in the psychosis spectrum. Relationships between memory processing and sleep characteristics have been described for schizophrenia, including unaffected first-degree relatives, but they are less clear across other high-risk groups within the psychosis spectrum. In this study, we investigated high-risk individuals with accumulated risk-factors for psychosis and subthreshold symptoms. Out of 1898 screened individuals, 44 age- and sex-matched participants were sub-grouped into those with substantial environmental risk factors for psychosis and subthreshold psychotic symptoms (high-risk group) and those without these phenotypes (low-risk controls). Four groups (high/low risk, morning/evening training) were trained and tested in the laboratory for sustained attention, motor skill memory (finger-tapping task) and declarative memory (word-pair learning task) immediately after training, again after a night of EEG-recorded sleep at home or a period of daytime wakefulness, and again after 24 h from training. No differences in sustained attention or in memory consolidation of declarative and motor skill memory were found between groups for any time period tested. However, a group difference was found for rapid-eye movement (REM) sleep in relation to motor skill memory: the longer the total sleep time, particularly longer REM sleep, the greater the performance gain, which occurred only in high-risk individuals. In conclusion, our results suggest a gain in motor skill performance with sufficient sleep opportunity for longer REM sleep in high-risk individuals with subthreshold psychotic symptoms. Declarative memory did not benefit from sleep consolidation above or beyond that of the control group.