The Effects of Repetitive Transcranial Magnetic Stimulation over the Left Dorsolateral Prefrontal Cortex on Anhedonia Symptoms in Treatment-Resistant Major Depressive Disorder

Abstract

Anhedonia is one of the core features of major depressive disorder, but treatment has proven to be difficult. Effects of antidepressants on symptoms of anhedonia may be related to their ability to alter dopamine neurotransmitter reward-systems. This warrants research to search for therapies that can specifically target these neuronal pathways. Repetitive transcranial magnetic stimulation (rTMS) over the dorsolateral prefrontal cortex (DLPFC) has this ability and might therefore be a promising therapy for anhedonia. The current study examines the effects of rTMS over the left DLPFC on anhedonia symptoms in a series of patients with moderate to severe, unipolar, treatment-resistant depression. This randomized controlled trial involved an intervention of 8 weeks of rTMS treatment and subsequent follow-up six months later. The severity of depression and anhedonia symptoms (measured with the HDRS-17 and SHAPS respectively) were assessed at baseline, after the treatment and at the six-month follow-up. Primary results were analyzed using a linear mixed model, with SHAPS scores as the dependent variable. Secondary outcomes include calculations of response and recovery rates regarding anhedonia symptoms after treatment. The analysis revealed a significant main effect of treatment group and time on the SHAPS-scores, with a significant decrease in SHAPS scores after 8 weeks of treatment rTMS treatment. The effects were long-lasting as the same results were seen at the 6 month follow-up. 45% of patients showed a considerable decline in anhedonia (>50%) after rTMS treatment, and 27% even reached full recovery. This study, therefore, indicates that rTMS could be an effective treatment for reducing anhedonia symptoms in MDD, but more extensive research is needed before it can be used in clinical practice.