Effects of transcranial direct current stimulation on COVID-19 neurological symptoms: a mini-review

Introduction: COVID-19 patients can experience long-term effects including neurological symptoms as part of the long COVID syndrome. The most common neurological symptoms associated with this syndrome are cognitive impairments, such as brain fog, memory issues or loss of concentration, and mood changes, such as depression and anxiety. Non-invasive brain stimulation, for instance, transcranial direct current stimulation (tDCS), is a treatment currently being tested to improve cognitive deficits and mood disorders in long COVID. Methods: We performed a systematic literature search for articles on long COVID and non-invasive brain stimulation. Electronic searches were performed in MEDLINE (via PubMed) and Cochrane databases. The Joanna Briggs Institute Critical Appraisal tool was used for quality assessment. Data regarding population, intervention, outcomes, study design, and sources of funding were collected. Results: The search returned 21 articles, of which two case reports were included in the discussion. Three patients with long COVID and cognitive symptoms were treated with tDCS. Although these studies reported promising results, they had methodological differences, no control groups were used and the sample size is insufficient to draw definitive conclusions. Discussion: Neuromodulation treatments like tDCS are currently being considered to treat long COVID, since they have been found to improve cognition, but so far only in observational studies with few patients. In the future, randomized clinical trials using tDCS for long COVID patients with cognitive impairment might demonstrate the effectiveness of this intervention.