# Biomarker use in predicting transcranial direct-current stimulation (tDCS) response: a systematic scoping review

## TL;DR

This paper reviews biomarkers that could predict how well people respond to tDCS, a brain stimulation treatment for neuropsychiatric conditions.

## Contribution

The study systematically identifies candidate biomarkers for tDCS response prediction across multiple neuropsychiatric disorders.

## Key findings

- Functional connectivity was the most common biomarker across 7 of 10 disorder categories.
- EEG features and cortical activation were also frequently reported as predictive biomarkers.
- Biomarkers with strong evidence had plausible mechanisms and prior research support.

## Abstract

Trans-cranial Direct Current Stimulation (tDCS) is a non-invasive neuromodulation technique with increasing evidence of efficacy in treating neuropsychiatric conditions. There is a need for biomarkers to predict and monitor tDCS efficacy. We aimed to conduct a systematic scoping review to assess the evidence regarding the ability of biomarkers to predict response to tDCS and identify promising candidate biomarkers in neuropsychiatric patient populations.

Comprehensive searches were conducted in the MEDLINE and EMBASE databases on 24/09/2023. Articles were screened at the title and abstract level and then at full text, and inclusion/exclusion criteria applies. Data was extracted and the quality of the studies assessed with the JADAD, MINORS and Ottawa rating scales. 154 including 154 studies in the review. Disorders studied weredivided into 10 categories, Stroke/Aphasia, Psychotic Disorders, Affective Disorders, Neurocognitive Disorders, Pain Disorders, Addiction Disorders, Disorders of Consciousness, Multiple Sclerosis, Neurodevelopmental Disorders and Traumatic Brain Injury. Biomarkers with positive results in at least 2 studies in each group were identified.

The most common biomarker across groups was functional connectivity, appearing in 7 of 10 groups. This was followed by EEG features and Cortical Activation. The biomarkers with most evidence have plausible mechanisms of action and have been previously proposed as candidate biomarkers in similar research. Other biomarkers included anatomical and clinical features, and levels of neurotransmitters in the brain.

This review identified the most promising candidate biomarkers in predicting and monitoring tDCS response in neuropsychiatric disorders and this may provide a focus for future research.

https://osf.io/r6mkp/?view_only=64ec4811e21f43ba84fe31496f403ec2.