Exercise-induced attenuation of the lateral habenula: a multi-axial quantitative synthesis of circuit-level resilience in depression.

BACKGROUND: Depression is characterized by pathological lateral habenula (LHb) hyperactivity within the anti-reward circuitry. However, a unified framework explaining how exercise modulates this specific circuit remains to be established.Aims: To examine whether neurobiological evidence supports the Network-Mediated Habenular Attenuation (NMHA) Model, which proposes exercise as a systemic regulator of LHb pathology. METHODS: A systematic synthesis was conducted following PRISMA guidelines and registered in PROSPERO. After a comprehensive search, 12 eligible studies met eligibility criteria. A quantitative synthesis was performed using a random-effects model, with Hedge's g used to estimate the magnitude of neuroplastic changes across the NMHA axes. RESULTS: Evidence suggests that exercise modulates LHb bursting via four convergent axes: (1) muscle-brain (peripheral-metabolic); (2) sensory-motor (monoaminergic); (3) cognitive-executive (top-down); and (4) hippocampal neurogenic (contextual). Quantitative synthesis revealed a robust global effect size (Hedges'g = 0.94; 95% CI [0.59, 1.29]). Heterogeneity was low (I2 = 14.90%). Some axes exhibited large effect sizes, with the hippocampal-contextual axis showing the highest potency (Hedges'g [1.95, 2.63]). These magnitudes provide a compensatory counter-signal to the pathological LHb burst firing observed in depressive states (Hedges'g ≈ 1.00), providing mathematical support for the NMHA model. DISCUSSION: Exercise potentially acts as a circuit-breaker for anhedonia by modulating the anti-reward architecture. The observed variability in effect sizes (95% Prediction Interval: 0.21, 1.67) indicates that future studies may report effect sizes ranging from small to very large, reflecting the influence of different exercise protocols and depression models on circuit attenuation. CONCLUSION: The NMHA model positions exercise as a targeted neuromodulatory strategy. Future research should leverage high-field neuroimaging to translate these preclinical circuit-level findings into human clinical populations.