title: Sleep/wake cycle disturbance in Alzheimer's disease: how much is due to an inherent trait?
abstract: Major advances in understanding the physiology and genetics of circadian rhythm in the past decade challenge the researcher of sleep/wake disorders in Alzheimer's disease (AD) to distinguish patient characteristics stable across the course of illness ("traits") from characteristics that vary with stage of illness ("states"). A components-of-variance approach with a repeated measures model was used to examine the between-subjects variance over time ("trait") vs. within-subjects ("state") variance in 42 patients with probable AD followed, on average, over 2 years on actigraphic sleep/wake measures. Mental status scores indexed stage of illness. Actigraphic measures of sleep efficiency and circadian rhythmicity appeared predominantly "trait," with between-individual differences accounting for over 55% of variance compared to the less than 5% of variance related to stage of cognitive impairment. We discuss how "state-trait" analyses can be helpful in identifying areas of assessment most likely to be fruitful objectives of physiologic and genetic research on sleep/wake disturbance in AD.
authors.affiliation: Department of Veterans Affairs Health Care System, Palo Alto, California 94304, USA. yesavage@stanford.edu
authors.forename: Jerome A
authors.initials: JA
authors.lastname: Yesavage
authors.forename: Joy L
authors.initials: JL
authors.lastname: Taylor
authors.forename: Helena
authors.initials: H
authors.lastname: Kraemer
authors.forename: Art
authors.initials: A
authors.lastname: Noda
authors.forename: Leah
authors.initials: L
authors.lastname: Friedman
authors.forename: Jared R
authors.initials: JR
authors.lastname: Tinklenberg
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000544:Alzheimer Disease / Q000145:classification / Q000150:complications* / Q000175:diagnosis / Q000235:genetics*; D000704:Analysis of Variance; D018450:Disease Progression; D005260:Female; D020022:Genetic Predisposition to Disease / Q000235:genetics*; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008609:Mental Status Schedule; D017286:Polysomnography; D012720:Severity of Illness Index; D012894:Sleep Stages; D012893:Sleep Wake Disorders / Q000175:diagnosis* / Q000209:etiology* / Q000503:physiopathology