Transcranial direct current stimulation and cognitive training in the treatment of cognitive deficit in schizophrenia: a randomized controlled trial

Cognitive impairment is a core feature of schizophrenia spectrum disorders and a major contributor to functional impairment in patients with the disorder. Given the limited effects of pharmacological treatments on cognition, there is an increasing interest in the use of alternative therapeutic approaches, including cognitive training and non-invasive brain stimulation. Our study aimed to evaluate the effectiveness of the combined treatment of tDCS and cognitive training on improving cognitive functions in patients with schizophrenia. This one-week, randomized, double-blind, placebo-controlled trial explored the effects of the combined intervention of anodal tDCS to the left dorsolateral prefrontal cortex and computer-based cognitive training on cognitive functions in schizophrenia. 30 clinically stable patients, aged 18 to 50 years, with an ICD-10 diagnosis of schizophrenia were randomized into two groups for five daily sessions of cognitive training and sham or active tDCS. Anodal tDCS (2 mA) was applied with the anode over left DLPFC (F3) and the cathode over the right orbitofrontal region (Fp2). Computer-based cognitive training was used. Cognitive testing was performed using the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS, versions A and B). 29 out of the 30 enrolled patients completed the study, and the data was analyzed. Although no statistically significant differences were detected, numerical trends across several RBANS domains (Total Score, Memory, Visuoconstructional, and Language indices) were slightly higher in the active stimulation group. The attention score was numerically higher in the sham group, but also did not reach a statistically significant level. The combined intervention of tDCS and cognitive training did not demonstrate significant superiority over cognitive training alone. Nevertheless, numerical trends in memory-related domains suggest potential for benefit. These findings contribute to the growing body of research on neuromodulation in schizophrenia, underscoring both the promise and the challenges of implementing combined therapeutic approaches in clinical practice. The trial was retrospectively registered in the ISRCTN registry (https://doi.org/10.1186/ISRCTN13247154) on 18/08/2021.