Although tDCS continues to be investigated for treating a variety of physical and mental disorders, it holds great promise in the treatment of depression, especially for those who do not respond to antidepressants and psychotherapy or who need additional help beyond traditional treatments.
There have been a number of published clinical trials to date testing the effectiveness of tDCS against sham (placebo) and other treatments. Below, I review recent (post-2019) meta-analyses regarding its effectiveness for treating depression.
Fregni and colleagues (2021) reviewed 15 clinical trials of tDCS for major depressive disorder, most of which compared TDCS to a sham condition or another type of therapy. The number of treatment sessions varied from 5 to 22. About half of these studies showed a positive result for tDCS effectiveness compared to controls. However, number of sessions was typically fewer than recommended, potentially affecting results. Their meta-analysis of 13 studies showed that anodal placement on the left DLPFC (dorsolateral pre-frontal cortex) location was most effective at treating depression (p. 35).
Citation: Fregni, F. et al. (2021). Evidence-based guidelines and secondary meta-analysis for the use of transcranial direct current stimulation in neurological and psychiatric disorders. International Journal of Neuropsychopharmacology, 24(4), 256-313. doi:10.1093/ijnp/pyaa051.
Hyde and colleagues compared effectiveness of both TMS and tDCS (called non-invasive brain stimulation or NIBS) across a variety of different disorders including depression, bipolar disorder, schizophrenia, OCD, and others. A combined total of 208 randomized controlled trials were meta-analyzed regarding symptom improvement and changes in cognitive functioning (attention, working memory, etc.) compared to sham (placebo).
tDCS was significantly better than sham at treating depression, substance-use disorders, and some symptoms of schizophrenia, but not anxiety disorders. tDCS significantly improved working memory and attention in schizophrenic patients. The effects of tDCS on cognitive functioning may be due to increased dopamine activity. Not included in the article was an explanation of the number of tDCS sessions or site of cortical stimulation for included studies.
Citation: Hyde, J., Carr, H., Kelley, N., Seneviraten, R., Reed, C., Parlatini, V., Garner, M., Solmi, M., Rossin, S., Cortese, S., & Brandt, V. (2022). Efficacy of neurostimulation across mental disorders: Systematic review and meta-analysis of 208 randomized controlled trials. Molecular Psychiatry, 27, 2709-2719. https://doi.org/10.1038/s41380-022-01524-8
Also published in 2022 was another NIBS (tDCS or TMS) meta-analysis. Previous research has proposed that using a combined approach of tDCS with other well-established depression treatments, including pharmacology or psychotherapy, could lead to better outcomes than using tDCS alone. A meta-analysis was conducted to determine if combining non-invasive transcranial stimulation, or NIBS, with psychotherapy would result in better outcomes than using either intervention alone.
Seventeen studies of 660 patients measured the reduction in depressive symptoms in patients. Control conditions included psychotherapy alone, sham NIBS plus psychotherapy or NIBS alone. Only the NIBS combined with psychotherapy yielded a significant positive reduction in depression. NIBS alone or sham NIBS plus psychotherapy were not significant.
When patients were grouped by severity of symptoms, minimal-to-mild depression or moderate-to-severe depression, significant differences between groups were found. The combined approach did not lead to improved outcomes for those with mild depression, compared to control conditions. This may be due to the effectiveness of NIBS alone or psychotherapy alone for patients with mild depression. However, for patients with moderate-to-severe depression, combining psychotherapy with NIBS reduced depression significantly compared to control conditions. Therefore, a combined approach may be the best treatment option for people with moderate-to-severe depression.
Citation: He, J., Tang, Y., Lin, J., Faulkner, G., Tsang, H. W. H., & Chan, S. H. W. (2022). Non-invasive brain stimulation combined with psychosocial intervention for depression: A systematic review and meta-analysis. BMC Psychiatry, 22: 273, 1-13.
Razza and colleagues focused their 2020 meta-analysis on studies comparing active vs. sham tDCS in reducing primary or secondary depression. Their analysis included 23 studies of 1092 patients published between 2006 and 2019, and approximately half of the participants received treatment and half received sham protocol. Results found that depression scores were significantly lower for the tDCS group, but with small to medium effect sizes. tDCS was more effective as a stand-alone rather than an add-on treatment (combined with pharmacotherapy or other treatment). All studies included the same montage (F3, F4), intensity varied from 0.5 to 2.5 mA, and number of sessions ranged from 5 to 20. Given the wide variability in the administration of tDCS across these studies (especially in number of sessions and intensity of electric current), it would be helpful to analyze a subset of studies with the highest number of sessions and amperage to determine if there is a stronger effect on depression symptoms.
Citation: Razza, L. B., Palumbo, P., Moffa, A. H., Carvahlo, A. F., Solmi, M., Loo, C. K., & Brunon, A. R. (2020). A systematic review and meta-analysis on the effects of transcranial direct current stimulation in depressive episodes. Depression and Anxiety, 1-15, https://doi.org/10.1002/da.23004
Summary: The number of meta-analyses published just since 2019 indicates the continuing interest in tDCS as a treatment for depression. Although studies of tDCS often have high heterogeneity (variability in results), there are numerous explanations that account for the heterogeneity, such as variation in number of treatment sessions, amperage, montage, and correct placement of electrodes. Given the fact that the number of sessions is typically quite low (15 or fewer) over a 1-2-week period in these studies, it is unclear if a longer treatment period would yield better results. Without consistent long-term follow-ups, it is difficult to determine the lasting effectiveness of tDCS.
In my next post, I will review research on treating depression using home-based tDCS devices.
©Jennie Dilworth, Ph.D