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Irregular sleep–wake cycles and cognitive impairment are frequently observed in schizophrenia, however, how they interact remains unclear.
To investigate the repercussions of circadian rhythm characteristics on cognitive performance and psychopathology in individuals with schizophrenia.
Fourteen middle-aged individuals diagnosed with schizophrenia underwent continuous wrist actimetry monitoring in real-life settings for 3 weeks, and collected saliva samples to determine the onset of endogenous melatonin secretion as a circadian phase marker. Moreover, participants underwent multiple neuropsychological testing and clinical assessments throughout the study period.
Sleep–wake cycles in individuals with schizophrenia ranged from well entrained to highly disturbed rhythms with fragmented sleep epochs, together with delayed melatonin onsets and higher levels of daytime sleepiness. Participants with a normal rest–activity cycle (objectively determined by high relative amplitude of day/night activity) performed significantly better in frontal lobe function tasks. Stepwise regression analysis revealed that relative amplitude and age represented the best predictors for cognitive performance (Stroop colour–word interference task, Trail Making Test A and B, semantic verbal fluency task), whereas psychopathology (Positive and Negative Syndrome Scale) did not significantly correlate with either cognitive performance levels or the quality of sleep–wake cycles.
Consolidated circadian rhythms and sleep may be a prerequisite for adequate cognitive functioning in individuals with schizophrenia.
This chapter evaluates whether insomnia patients are sleepier than healthy controls without insomnia. In order to assess whether insomnia patients suffer from sleepiness, the authors assessed the extent to which treatments for insomnia improved some measure related to daytime sleepiness. The current literature suggests that insomnia is frequently associated with greater self-reported daytime sleepiness than is seen in healthy individuals without sleep complaints. The multicomponent cognitive-behavioral therapy had a significant advantage over the control therapy in decreasing number of naps per week. Some have hypothesized that this mismatch reflects a hyperarousal state in insomnia that prevents the daytime sleepiness that they experience from becoming manifest in objective daytime sleepiness. The findings of treatment studies provide preliminary evidence that insomnia patients have some degree of daytime sleepiness that can be improved with treatment.