Exploratory Associations of Sleep Spindles and Sleep Disordered Breathing Indices with Hippocampal and Thalamic Volume, and Cortical Thickness, and Cerebrovascular Biomarkers Among Community Dwelling Older Adults: Results from the Brain in Motion

Abstract Study Objectives Obstructive sleep apnea (OSA) impacts brain structure and cerebrovascular function and is often associated with impaired sleep microstructure such as sleep spindles. Given the lack of research in sleep spindles and brain physiology in community dwelling older adults, this exploratory study hypothesized that 1) sleep disordered breathing is associated with lower cortical thickness, thalamic volume, hippocampal volume, cerebral perfusion, and higher white matter hyperintensity volume; and 2) greater cortical thickness, thalamic and hippocampal volume predict greater sleep spindle density, frequency and percentage of fast spindles. Methods A total of seventy-one participants (males/females: 24/47) underwent magnetic resonance imaging, and sleep polysomnography (PSG). Results Apnea hypopnea index, oxygen desaturation index, and sleep fragmentation index were not related to daytime whole brain gray matter cerebral blood flow or white matter hyperintensity volume (all p>.05). Spindle frequency was associated with thalamic volume (β = 0.24, p=.03, 95% CI = 0.20-3.66) but this finding did not survive correction for multiple comparisons. Hippocampal volume and cortical thickness were not associated with sleep spindle characteristics (all p>.05). Conclusions Our findings suggest a potential structure–function relationship between the thalamus and spindle frequency. Our results also demonstrate that cerebral perfusion and white matter hyperintensities are not associated with OSA in community-dwelling older adults, potentially reflecting an ability of the cerebrovasculature to cope with relatively mild hypoxic insults. However, future studies should confirm these findings in a larger sample and consider the length of time in which participants experienced mild to moderately severe OSA (apnea hypopnea index <30).