Sleep influences the severity of memory disruption in amnestic mild cognitive impairment: results from sleep self-assessment and continuous activity monitoring

Abstract

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.

Figure 1

Overview of the tasks completed by participants on each of the 15 days of the protocol.

Figure 2

Recognition hit rates for amnestic MCI patients and controls averaged across 14 nights for each participant and then averaged across all participants for A) 24-hour recognition, B) immediate memory (from the continuous recognition test, lag = 0 intervening trials), and C) short-delay memory as a function of retention delay in the continuous recognition test, corrected for false alarms. Bars represent standard errors of the mean.

Figure 3

Standard deviations (SD) of the A) time in bed, B) actual sleep time, C) sleep latency, D) wake after sleep onset actigraphy measures, and E) ratings given to the Karolinska Sleep Diary question regarding how well participants slept throughout the time allotted for sleep across the 14 nights of the protocol, plotted against performance on the Logical Memory II delayed-recall score from the Wechsler Memory Scale–Revised (WMS-R).