Objectives: Nocturnal sleep disruption has been considered as a risk factor for cognitive impairment in the elderly. And the frontal lobe dysfunction was suggested to predict the progression to dementia. We aimed to illustrate the relationship of nocturnal sleep with frontal lobe function in mild cognitive impairment (MCI) patients.
Methods: Thirty MCI patients and 30 age- and sex-matched normal control (NC) subjects were selected. Frontal lobe function tests including Stroop Test, Similarity Test, Digit Span Test (DST), and Benton Visual Retention Test (BVRT) were administrated. Nocturnal polysomnography was done for each subject.
Results: There was no significant difference in the sleep parameters and diagnostic distributions of sleep disorders between the MCI and NC groups. In MCI patients, the mean hypopnea index (HI) of the ApoE4 positive group was higher than that of ApoE4 negative group. In the NC group, the wake time after sleep onset (WASO) was negatively correlated with the DST score (r=-0.545). In the MCI group, WASO tended to be negatively correlated with the Similarity Test score (r=-0.376, p=0.053), and slow wave sleep amount (SWS) was negatively correlated with the error score of BVRT (r=-0.489).
Conclusion: Although there was no difference in the sleep quality and frequency of SAS between the MCI and NC groups, the severity of SDB was higher in MCI patients with ApoE4 compared to those without ApoE4. In the MCI group, the difficulty in maintaining sleep was associated with decreased executive function, and the decreased SWS was associated with impaired working memory. The relationship of nocturnal sleep with the frontal lobe function in MCI patients appears to be different from that of normal elderly subjects.
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