Abstract
Abstract Aims In the search for effective therapeutic strategies for depression, repetitive transcranial magnetic stimulation (rTMS) emerged as a non-invasive, promising treatment. This is because the antidepressant effect of rTMS might be related to neuronal plasticity mechanisms possibly reverting connectivity alterations often observed in depression. Therefore, in this review, we aimed at providing an overview of the findings reported by studies investigating functional and structural connectivity changes after rTMS in depression. Methods A bibliographic search was conducted on PubMed, including studies that used unilateral, excitatory (⩾10 Hz) rTMS treatment targeted on the left dorsolateral prefrontal cortex (DLPFC) in unipolar depressed patients. Results The majority of the results showed significant TMS-induced changes in functional connectivity (FC) between areas important for emotion regulation, including the DLPFC and the subgenual anterior cingulate cortex, and among regions that are part of the major resting-state networks, such as the Default Mode Network, the Salience Networks and the Central Executive Network. Finally, in diffusion tensor imaging studies, it has been reported that rTMS appeared to increase fractional anisotropy in the frontal lobe. Limitations The small sample size, the heterogeneity of the rTMS stimulation parameters, the concomitant use of psychotropic drugs might have limited the generalisability of the results. Conclusions Overall, rTMS treatment induces structural and FC changes in brain regions and networks implicated in the pathogenesis of unipolar depression. However, whether these changes underlie the antidepressant effect of rTMS still needs to be clarified.
Highlights
Introduction and aimsDepressive disorders are one of the leading causes of disability worldwide, with a high impact on individuals and society in terms of medical costs and loss of productivity (Friedrich et al, 2017)
functional connectivity (FC) results focused on two brain areas, the dorsolateral prefrontal cortex (DLPFC) and the subgenual anterior cingulate cortex, whose connectivity emerged to be affected by the selected repetitive transcranial magnetic stimulation (rTMS) protocol
The results showed that FC changes in key areas involved in the emotion regulation (i.e. DLPFC and subgenual anterior cingulate cortex (sgACC)) and major resting-state networks (DMN, Central Executive Network (CEN), Salience Network (SN)) were found to be associated with rTMS treatment, possibly mediating rTMS therapeutic efficacy
Summary
Introduction and aimsDepressive disorders are one of the leading causes of disability worldwide, with a high impact on individuals and society in terms of medical costs and loss of productivity (Friedrich et al, 2017). Approximately 15–30% of MDD patients do not respond to two antidepressant drugs, defining the condition as treatment-resistant depression (TRD), which is associated with more severe cognitive impairment, increased comorbidities, increased risk of suicide and higher medical costs (Du et al, 2017; Garay et al, 2017). Various treatment strategies have been proposed for TRD, including both pharmacological and non-pharmacological approaches (McIntyre et al, 2014). Among the latter, various stimulation techniques have been approved for TRD, such as electroconvulsive therapy, vagus nerve stimulation, deep brain stimulation and repetitive transcranial magnetic stimulation (rTMS) (Akhtar et al, 2016). The ultimate effect is dependent on stimulation frequency, with high-frequency rTMS associated with increased neuronal excitability and low-frequency stimulations with decreased neuronal excitability (De Risio et al, 2020)
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