Bedtime Variability And Altered Effort Discounting Among College Students.

Abstract

Introduction: Sleep variability (intra-individual variability in bedtime and sleep duration) is prevalent among college students. The current study aims to investigate the associations between sleep variability and decision making behaviors. Methods: Sixty-six college students (16 males, age = 17–23 y) participated in the present study, which included the actigraphic sleep assessment (Actiwatch Pro, Philips Respironics, Inc.) for eight consecutive days, followed by the completion of computerized tasks in the laboratory. Sleep parameters derived from the actigraphy included the means and standard deviations (SD) of sleep onset time, sleep offset time, nocturnal sleep duration and wake-after sleep-onset. Sleep variability was represented by SD. Impulsive decision-making behaviors were measured by the Balloon Analogue Risk Task (BART) and the reward discounting task. Temporal discount (i.e., preference to smaller immediate rewards over larger delayed rewards) and effort discount (i.e., preference to typing less letters for smaller rewards over typing more letters for larger rewards) were reflected by the area under the curve (AUC), in which smaller AUCs suggesting more impatient choice pattern. Linear regression analyses were applied to examine the relationships between decision-making (dependent variables) and sleep variability (independent variables), in which gender, mental health, average sleep onset time and nocturnal sleep duration were included as covariates. Results: The average sleep onset time was 01:13 ± 1:17am, and the SD of sleep onset time was 1.17 ± 0.65 h. The average night sleep duration was 6.87 ± 0.95 h, and the SD of night sleep duration was 1.56 ± 0.66 h. Higher degree of variability in sleep onset time (as reflected by larger SD) was related with lower AUC in the effort discounting task, indicating a higher discount rate (ß = - 0.52, p < 0.001). However, no significant association was found between the performance in BART or temporal discounting of monetary rewards, and the variability in sleep parameters. Conclusion: Bedtime variability showed differential associations with discounting behaviors, which were similarly observed in individuals with sleep deprivation. In addition to sleep duration, the regularity of sleep-wake schedule may interfere with individual’s decision making especially when efforts are required.