Research on cardiac autonomic function in major depressive disorder (MDD) has predominantly examined cardiac vagal control and adopted a model of reciprocal autonomic balance. A proposed bivariate autonomic continuum uses cardiac autonomic balance (CAB) and cardiac autonomic regulation (CAR) models, derived from normalized values of respiratory sinus arrhythmia and pre-ejection period, to more adequately index patterns of autonomic control. The purpose of this study was to assess resting levels of CAB and CAR among young adults with and without a current diagnosis of major depression. One hundred forty-two young adults (n = 65 MDD, n = 77 healthy controls; 20.8 ± 2.6 years) completed a structured diagnostic interview, cardiovascular assessment, and a maximal aerobic fitness test. The findings revealed that CAB, but not CAR, significantly predicted current MDD status (OR = 0.70, 95% CI [0.53, 0.93]), an effect that remained after controlling for aerobic fitness and body mass index. Although CAB was found to be a significant predictor of current MDD status among a sample of young adults, there remained substantial variation in autonomic control that was not captured by the traditional model of reciprocal autonomic balance.
Reward sensitivity and emotional reactivity have been identified as two candidate mechanisms of anhedonia in depression. However, there is a paucity of research examining whether deficits in reward sensitivity and emotional reactivity can be modified through brief, behavioral interventions. Therefore, the purpose of this study was to examine the effects of continuous moderate-intensity aerobic exercise on the reward positivity (RewP) and late positive potential (LPP) among individuals reporting variable symptoms of depression. Using a within-subjects design, 66 young adults completed a 30-min session of aerobic exercise and seated rest on separate days. Reward sensitivity and emotional reactivity were assessed following each session using the RewP and LPP event-related brain potentials. Results indicated that the LPP to positive stimuli was potentiated following exercise, while no effect on RewP was observed. Notably, individuals who experienced greater emotional reactivity to positive stimuli following exercise also exhibited increased sensitivity to rewards. Depressive symptom severity failed to moderate any effects, suggesting beneficial effects of acute exercise on positive emotional reactivity across depressive symptom profiles. These findings suggest that aerobic exercise increases emotional engagement to positive stimuli, which may have implications for protecting against the development of anhedonia and resolving the blunted emotional reactivity to positive content in depression.
Background
Aerobic exercise has demonstrated antidepressant efficacy among adults with major depression. There is a poor understanding of the neural mechanisms associated with these effects. Deficits in reward processing and cognitive control may be two candidate targets and predictors of treatment outcome to exercise in depression.
Methods
Sixty-six young adults aged 20.23 years (s.d. = 2.39) with major depression were randomized to 8 weeks of moderate-intensity aerobic exercise (n = 35) or light stretching (n = 31). Depressive symptoms were assessed across the intervention to track symptom reduction. Reward processing [reward positivity (RewP)] and cognitive control [error-related negativity (ERN)] were assessed before and after the intervention using event-related brain potentials.
Results
Compared to stretching, aerobic exercise resulted in greater symptom reduction (gs = 0.66). Aerobic exercise had no impact on the RewP (gav = 0.08) or ERN (gav = 0.21). In the aerobic exercise group, individuals with a larger pre-treatment RewP [odds ratio (OR) = 1.45] and increased baseline depressive symptom severity (OR = 1.18) were more likely to respond to an aerobic exercise program. Pre-treatment ERN did not predict response (OR = 0.74).
Conclusions
Aerobic exercise is effective in alleviating depressive symptoms in adults with major depression, particularly for those with increased depressive symptom severity and a larger RewP at baseline. Although aerobic exercise did not modify the RewP or ERN, there is preliminary support for the utility of the RewP in predicting who is most likely to respond to exercise as a treatment for depression.
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