Combined Cognitive Training and Transcranial Direct Current Stimulation in Neuropsychiatric Disorders: A Systematic Review and Meta-analysis

Background: Treatments for cognitive dysfunction in neuropsychiatric conditions are urgently needed. Cognitive training and transcranial direct current stimulation (tDCS) hold promise, and there is growing interest in combined or multimodal treatments, though studies to date have had small samples and inconsistent results.

Methods: A systematic review and meta-analysis was completed. Retained studies included cognitive training combined with active or sham tDCS in a neuropsychiatric population and reported a posttreatment cognitive outcome. Meta-analyses included effect sizes comparing cognitive training plus active tDCS and cognitive training plus sham tDCS in 5 cognitive domains. Risk of bias in included studies and across studies was explored.

Results: Fifteen studies were included: 10 in neurodegenerative disorders and 5 in psychiatric disorders (n = 629). There were several tDCS montages, though two-thirds of studies placed the anode over the left dorsolateral prefrontal cortex. A wide variety of cognitive training types and outcome measures were reported. There was a small, statistically significant effect of combined treatment on measures of attention/working memory, as well as small and non-statistically significant effects favoring combined treatment on global cognition and language. There was no evidence of bias in individual studies but some evidence of nonreporting or small-study bias across studies.

Conclusions: These results may provide preliminary support for the efficacy of combined cognitive training and tDCS on measures of attention/working memory. More data are needed, particularly via studies that explicitly align the cognitive ability of interest, stimulation target, training type, and outcome measures.