An altered processing of negative salient stimuli has been suggested to play a central role in the pathophysiology of major depression (MD). Besides negative affective and social stimuli, physical pain as a subtype of negative sensory stimulation has been investigated in this context. However, the few neuroimaging studies on unpleasant sensory stimulation or pain processing in MD report heterogeneous findings. Here, we investigated 47 young females, 22 with MD and 25 healthy controls (HC) using fMRI (3.0 T). Four levels of increasingly unpleasant electrical stimulation were applied. Ratings of stimulus intensity were assessed by a visual analogue scale. fMRI-data were analyzed using a 2 × 4 ANOVA. Behavioral results revealed no group differences regarding accuracy of unpleasant stimulation level ratings and sensitivity to stimulation. Regarding neural activation related to increasing levels of unpleasant stimulation, we observed increasing activation of brain regions related to the pain and salient stimulus processing corresponding to increasingly unpleasant stimulation in controls. This modulation was significantly smaller in MD compared to controls, particularly in the dorsal anterior cingulate cortex, the somatosensory cortex, and the posterior insula. Overall, brain regions associated with the processing of unpleasant sensory stimulation, but also associated with the salience network, were highly reactive but less modulated in female patients with MD. These results support and extent findings on altered processing of salience and of negative sensory stimuli even of a non-painful quality in female patients with MD.
Keywords: Depression; Electric stimulation; Somatosensory processing; Unpleasant sensory stimulation; fMRI.