Associations between locus coeruleus MRI contrast and physiological responses to acute stress in younger and older adults

Abstract

Acute stress robustly activates the brain's noradrenergic system, the hub of which is the locus coeruleus (LC). Recent studies have indicated that structural integrity of the LC, assessed through magnetic resonance imaging (MRI), is associated with better cognitive outcomes in later life. However, no studies have examined whether MRI-assessed LC integrity is related to arousal responses to acute stress in either younger or older adults, despite the LC's documented role in promoting physiological arousal as part of the acute stress response. In this study, 102 younger and 51 older adults completed an acute stress induction task while we assessed multiple measures of physiological arousal (heart rate, breathing rate, systolic and diastolic blood pressure, sympathetic tone, and heart rate variability, HRV). We used turbo spin echo MRI scans to quantify LC MRI contrast as a measure of LC integrity. Using univariate and multivariate approaches, we assessed how LC MRI contrast was associated with arousal at rest and during acute stress reactivity and recovery. We found that in older adults, having higher caudal LC MRI contrast was associated with greater stress-related increases in systolic blood pressure and decreases in HRV, as well as lower HRV during recovery from acute stress. These results suggest that having higher caudal LC integrity in older adulthood is associated with more pronounced physiological responses to acute stress. Further work is needed to confirm these patterns in larger samples of older adults.