Effects of tDCS on brain function in patients with post-stroke cognitive impairment: a randomised controlled study protocol based on TMS and fNIRS

BACKGROUND: Transcranial direct current stimulation (tDCS) positively affects post-stroke cognitive impairment (PSCI). However, the optimal stimulation protocol remains unclear, possibly because of the lack of objective assessment methods. Therefore, this study aims to investigate the impact of tDCS on the modulation of the excitation/inhibition (E/I) balance and its effects on brain function in patients with PSCI using transcranial magnetic stimulation (TMS) and functional near-infrared spectroscopy (fNIRS). METHODS: This study is a single-centre, two-armed randomised controlled trial. A total of 40 patients with PSCI will be recruited and randomly assigned to real and sham tDCS groups in a 1:1 ratio. Both groups will receive either real or sham tDCS in addition to conventional treatment. In both groups, electrodes will be placed at the same positions, with the anode and cathode above the left and right dorsolateral prefrontal cortex, respectively. The real tDCS group will receive continuous current throughout the session, whereas the sham tDCS group will receive current generation for only the first 30 s. The treatment will consist of a 3-week intervention with one session per day, five sessions per week and 30 min per session. A 4-week follow-up will be conducted at the end of the treatment. The primary outcome is the change in Montreal cognitive assessment (MoCA) scores from baseline (T0) to immediately post-intervention (T1). Secondary outcomes include Barthel index, levels of intracortical inhibition measured by TMS and cortical activation and interhemispheric connectivity assessed by fNIRS during a Stroop task. DISCUSSION: This study will combine TMS and fNIRS to explore the effects of tDCS on the modulation of the E/I balance and its impact on blood oxygen levels and neural activity. Our results are expected to provide a clinical reference for the development of more precise tDCS protocols. TRIAL REGISTRATION: Chinese Clinical Trials Registry ChiCTR2300077453. Registered on November 9, 2023.