Sleep-wake cycles and cognitive functioning in schizophrenia.
BACKGROUND
Irregular sleep-wake cycles and cognitive impairment are frequently  observed in schizophrenia, however, how they interact remains unclear.


OBJECTIVE
To investigate the repercussions of circadian rhythm characteristics on  cognitive performance and psychopathology in individuals with  schizophrenia.


METHODS
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.


RESULTS
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.


CONCLUSIONS
Consolidated circadian rhythms and sleep may be a prerequisite for adequate  cognitive functioning in individuals with schizophrenia.
Centre for Chronobiology, Psychiatric Hospital, University of Basel, Switzerland.
Vivien
V
Bromundt
Matthias
M
Köster
Angela
A
Georgiev-Kill
Klaus
K
Opwis
Anna
A
Wirz-Justice
Gabriela
G
Stoppe
Christian
C
Cajochen
D056044:Actigraphy / Q000706:statistics & numerical data; D000328:Adult; D002940:Circadian Rhythm / Q000502:physiology; D003072:Cognition Disorders / Q000378:metabolism / Q000503:physiopathology*; D005260:Female; D006801:Humans; D008297:Male; D008550:Melatonin / Q000378:metabolism; D008875:Middle Aged; D009043:Motor Activity / Q000502:physiology; D009483:Neuropsychological Tests; D011569:Psychiatric Status Rating Scales; D012463:Saliva / Q000378:metabolism; D012559:Schizophrenia / Q000378:metabolism / Q000503:physiopathology*; D012565:Schizophrenic Psychology; D012890:Sleep / Q000502:physiology; D020178:Sleep Disorders, Circadian Rhythm / Q000378:metabolism / Q000503:physiopathology*; D013223:Statistics as Topic
D008550:Melatonin