Sleep is important for declarative memory consolidation in healthy adults. Sleep disruptions are typical in Alzheimer disease, but whether they contribute to memory impairment is unknown. Sleep has not been formally examined in amnestic mild cognitive impairment (aMCI), which is characterized by declarative-memory deficits without dementia and can signify prodromal Alzheimer disease. We studied 10 aMCI patients and 10 controls over 2 weeks using daily sleep surveys, wrist-worn activity sensors, and daily recognition tests. Recognition was impaired and more variable in aMCI patients, whereas sleep was similar across groups. However, lower recognition of items learned the previous day was associated with lower subjective sleep quality in aMCI patients. This correlation was not present for information learned the same day and thus did not reflect nonspecific effects of poor sleep on memory. These results indicate that inadequate memory consolidation in aMCI patients is related to declines in subjective sleep indices. Furthermore, participants with greater across-night sleep variability exhibited lower scores on a standardized recall test taken prior to the 2-week protocol, suggesting that consistent sleep across nights also contributes to successful memory. Physiological analyses are needed to further specify which aspects of sleep in neurological disorders impact memory function and consolidation.
Department of Psychology, Northwestern University, Evanston, IL
This study was sponsored by the Alzheimer Association (Principal investigator: K.A.P.; HAT-08-86763), The Alzheimer Disease Research Fund of the State of Illinois, Department of Public Health (Principal investigator: K.A.P.); The American Health Assistance Foundation (research fellowship awarded to C.E.W.; A2008-663); and the National Institute of Aging (support for the Northwestern University Cognitive Neurology and Alzheimer Disease Center, PI: M.M.; P30 AG13854).
None of the authors have any conflicts of interest with the present study.
Reprints: Carmen E. Westerberg, PhD, Department of Psychology, Northwestern University, 2029 Sheridan Road, Evanston, IL 60208 (e-mail: firstname.lastname@example.org).
Received November 10, 2009
Accepted April 6, 2010