Objective: While research on sleep and cognition
has largely focused on mean values of sleep measured across multiple nights, few studies have examined the potentially negative effects of night-to-night variability in sleep quality on brain function. The purpose of this study was to determine the relationship between variability in sleep quality and spatial learning and memory in young adults. We hypothesized that greater intraindividual sleep efficiency variability (SEv) would predict poorer spatial learning and recall performance.

Participants and Methods: University students from the Bronx, NY (N=188; mean age=20.4) wore an at-home actigraphic device (Actiwatch Spectrum PRO; Philips Respironics Inc.) on the non-dominant wrist for an average of 10.5 days (range 6.8–21.0) to measure objective sleep behavior. Participants then returned to the laboratory and were administered neuropsychological tests. SEv was calculated as the intraindividual coefficient of variation (SD/M x 100) of the percentage of time spent asleep in the sleep interval. Spatial learning and memory were assessed using the maze efficiency index scores (correct moves per second) of the Cogstate Groton Maze Learning Tests (GMLT learning average, GMLT learning slope, GMLT recall).

Results: Linear regression showed that SEv predicted lower performance on tests of spatial learning (GMLT learning average; β=-.23, p<.01 and GMLT learning slope; β=-.18, p<.05) and recall (GMLT recall; β=-.17, p<.05). Even after controlling for average total sleep time, SEv remained a predictor of poorer learning and memory across all GMLT measures (ps<.05).

Conclusions: Intraindividual variability in sleep quality predicts worse spatial learning and memory in young adults. Significant effects of SEv were over and above that of average total sleep time, suggesting unique contributions of variable sleep quality beyond mean sleep quality. Results highlight the importance of maintaining consistent sleep patterns for optimal cognitive functioning.