Anhedonia across borders: Transdiagnostic relevance of reward dysfunction for noninvasive brain stimulation endophenotypes

Introduction: Anhedonia is a transdiagnostic psychopathological dimension, consisting in the impaired ability to experience pleasure. In order to further our understanding of its neural correlates and to explore its potential relevance as a predictor of treatment response, in this article we systematically reviewed studies involving anhedonia and neuromodulation interventions, across different disorders. Methods: We included seven studies fulfilling inclusion/exclusion criteria and involving different measures of anticipatory and consummatory anhedonia, as well as different noninvasive brain stimulation interventions (transcranial magnetic stimulation and transcranial direct current stimulation). Studies not exploring hedonic measures or not involving neuromodulation intervention were excluded. Results: All the included studies entailed the use of rTMS protocols in one of the diverse prefrontal targets. The limited amount of studies and the heterogeneity of stimulation protocols did not allow to draw any conclusion with regard to the efficacy of rTMS in the treatment of transnosographic anhedonia. A potential for anhedonia in dissecting possible endophenotypes of different psychopathological conditions preliminarily emerged. Conclusions: Anhedonia is an underexplored condition in neuromodulation trials. It may represent a valuable transdiagnostic dimension that requires further examination in order to discover new clinical predictors for treatment response.