In patients with unipolar and bipolar depression, high-dose and low-dose transcranial direct current stimulation (tDCS) may improve verbal learning and recall, working memory, selective attention, and information processing. Genotype may also moderate the neurocognitive effects of this treatment, according to results of a triple-masked, randomized controlled clinical trial published in Depression and Anxiety.
Patients with unipolar and bipolar depression from 6 international academic centers were randomly assigned to either high-dose tDCS at 2.5 mA for 30 minutes (n=61; 42 unipolar) or sham low-dose tDCS at 0.034 mA for 30 minutes (n=59; 42 unipolar), totaling 20 sessions during a 4-week study period. After these 4 weeks, participants had the option to continue to a 4-week open-label high-dose treatment period. In treatment, tDCS anodes were placed over the left dorsolateral prefrontal cortex. Clinical and neurocognitive assessments were completed by all participants before and after each tDCS treatment. The researchers assessed the role of genotype, including BDNF Val66Met and catechol-o-methyltransferase (COMT) Val158Met polymorphisms, in moderating neurocognitive effects.
In patients with unipolar depression, treatment with low-dose and high-dose tDCS resulted in improvements in verbal learning and working memory (P <.001), selective attention (Ruff 2 and 7 total speed t score [P =.014] and total accuracy t score [P =.001]), and information processing speed (P =.035). For patients with bipolar depression, both low-dose and high-dose tDCS were also associated with improvements in verbal learning and working memory (P <.001), selective attention (Ruff 2 and 7 total speed t score [P = .002] and total accuracy t score [P = .022]), and information processing speed (P =.006). There was an interaction effect between tDCS dose and the presence of BDNF Val66Met and COMT Val158Met polymorphisms, which affected verbal memory and verbal fluency outcomes, respectively.
Limitations of the study included the small number of patients in the bipolar disorder sample. The researchers suggest that further validation studies could be “clinically important as such investigation could provide information to develop personalized tDCS therapeutic approaches to target specific cognitive functions and improve the utility and efficacy of this noninvasive neuromodulation treatment” in patients with depression.
McClintock SM, Martin DM, Lisanby SH, et al. Neurocognitive effects of transcranial direct current stimulation (tDCS) in unipolar and bipolar depression: findings from an international randomized controlled trial [published online January 16, 2020]. Depress Anxiety. doi: 10.1002/da.22988.