0263 Later Bedtime is Associated with Differences in Prefrontal Gray Matter Volume and Executive Function Deficits

Abstract

Abstract Introduction Evening chronotypes tend to have reduced white matter integrity within their axonal tracts and reduced functional connectivity compared to morning types, a pattern that has been attributed to chronic “social jet lag” and its attendant disrupted sleep patterns. It is not clear whether brain differences are due to chronotype, total sleep time (TST), or whether they are associated with actual bedtime exclusive of these other factors. Here we examined morphometric gray matter volume (GMV) and its correlation with bedtime, after controlling for confounding factors. Methods Forty-five healthy adults (22 female; aged 20 to 43), completed the Horne-Ostberg Morningness-Eveningness Questionnaire (MEQ) and the Tower of London (TOL), an executive function task of planning and sequencing. Participants wore an actigraph for 7 days and completed structural MRI imaging during the period of actigraphy. Morphometric GMV data were processed using standard procedures in SPM12. After controlling for age, sex, and intracranial volume, actigraphic bedtime was entered into a regression analysis to predict orbitofrontal GMV. Regional GMV was extracted and correlated with TOL performance. Effects of TST and MEQ were also examined during regression. Results Later bedtime was associated with increased GMV in the left superior orbitofrontal gyrus (p=.044, FWE corrected). This association remained significant after controlling for TST and MEQ. Moreover, greater GMV in this cluster was associated with poorer planning and sequencing on TOL in terms of excess moves (r=.357, p=.017), and faster response times (r=-.356, p=.018), suggesting impulsivity. Conclusion Later bedtime was associated with greater GMV of the orbitofrontal cortex, even after controlling for TST and chronotype, and this pattern was associated with greater impulsiveness and poorer planning. The causal direction of the relationship between bedtime and executive deficits remains unclear and will require further research. However, it is clear that sleep patterns, brain structure, and behavior are intimately related. Support Defense Advanced Research Projects Agency Young Faculty Award: DARPA-12-12-11-YFA11-FP-029