Background: Social touch is an integral part of social relationships and has been associated with reward. Major depressive disorder (MDD) is characterized by severe impairments in reward processing, but the neural effects of social touch in MDD are still elusive. In this study, we aimed to determine whether the neural processing of social touch is altered in MDD and to assess the impact of antidepressant therapy.
Methods: Before and after antidepressant treatment, 53 MDD patients and 41 healthy controls underwent functional magnetic resonance imaging (fMRI) while receiving social touch. We compared neural responses to social touch in the reward network, behavioral ratings of touch comfort and general aversion to interpersonal touch in patients to controls. Additionally, we examined the effect of treatment response on those measures.
Results: Clinical symptoms decreased after treatment and 43.4% of patients were classified as responders. Patients reported higher aversion to interpersonal touch and lower comfort ratings during the fMRI paradigm than controls. Patients showed reduced responses to social touch in the nucleus accumbens, caudate nucleus and putamen than controls, both before and after treatment. Contrary to our hypotheses, these effects were independent of touch velocity. Non-responders exhibited blunted response in the caudate nucleus and the insula compared to responders, again irrespective of time.
Conclusions: These findings suggest altered striatal processing of social touch in MDD. Persistent dysfunctional processing of social touch despite clinical improvements may constitute a latent risk factor for social withdrawal and isolation.
Keywords: fMRI; major depression; reward; social touch.