Acute stress enhances emotional face processing in the aging brain

Background: Healthy aging has been associated with stable emotional wellbeing and attenuated brain responses to negative stimuli. At the same time, depressive symptoms are common in older adults. The neural mechanisms behind this paradox remain to be clarified. We hypothesized that acute stress could alter emotion processing in the healthy aging brain, and therefore constitute a pathway to vulnerability. Methods: Using a randomized, controlled cross-over design we explored the influence of acute stress on brain responses to happy and fearful facial expressions in 25 older adults (aged 60-75) and 25 young (aged 18-30) controls. Groups were matched on trait anxiety and education. Subjects each underwent two separate fMRI sessions involving acute stress or a control procedure. Results: Affective and physiological responses to the stressor were similar between the two age groups. On whole-brain level, we revealed a significant age by stress interaction in the fusiform gyrus, indicating a selective enhancement of neural activity with stress in the elderly only. When specifically aiming our analysis at the amygdala, we found the same stress-related increase in activity in the elderly only. The modulation of amygdala reactivity due to stress correlated with trait conscientiousness in the elderly exclusively. Conclusions: Healthy, older adults showed increased responsivity of brain regions involved in face and emotion processing while stressed, compared with younger adults. These findings suggest that increased reactivity of this neural circuitry after acute stress may constitute one mechanism by which emotional wellbeing during healthy aging could rapidly change into heightened vulnerability for affective disorders