ALTERED REWARD–SENSORIMOTOR NETWORK CONNECTIVITY IS ASSOCIATED WITH REDUCED MOVEMENT IN DEPRESSION BUT NOT IN FIBROMYALGIA

Patients with depression exhibit anhedonia as a core symptom, suggesting dysfunction in reward processing. The ventral tegmental area (VTA) is a subcortical region within the reward system that encodes reward prediction error (Bayer & Glimcher, 2005) and is anatomically connected to sensorimotor regions involved in movement and somatosensory processing (Hosp et al., 2019). Altered VTA connectivity has been associated with anhedonia (Geugies et al., 2019), and this region is also implicated in chronic pain and pain sensitization (Yu et al., 2020). The present study aims to investigate functional connectivity alterations in the VTA during resting-state in patients with major depression (MDD) and fibromyalgia (FM). For this purpose, we included 33 women with major depression, 61 women with fibromyalgia, and 51 age‑matched healthy controls. All participants underwent resting‑state functional magnetic resonance imaging and completed clinical assessments. Seed‑based functional connectivity analyses targeted the VTA, and post‑hoc analyses examined associations between connectivity patterns and daily movement behaviour, quantified via AX3 accelerometer data. Our analysis revealed increased connectivity between the VTA and the left postcentral gyrus (S1) in MDD relative to FM (pFWE-cluster < 0.05, whole-brain; p-voxel < 0.001). Remarkably, this connectivity was associated with a lower daily step count (r = –0.52, p = 0.02), exclusively in the MDD group. These findings revealed a disorder-specific connectivity alteration in MDD compared to FM: increased functional connectivity between the VTA and somatosensory-motor regions correlated with reduced daily movement, potentially representing a neural mechanism underlying psychomotor retardation in MDD.