Prefrontal Hemodynamics Underlie the Synergistic Effect of Tai Chi Combined with Transcranial Direct Current Stimulation on Memory in Patients with MCI: An Exploratory fNIRS Study

Objective Memory dysfunction is a major concern in patients with mild cognitive impairment (MCI) and is closely associated with changes in prefrontal cortex (PFC) hemodynamics. Tai Chi (TC) combined with transcranial direct current stimulation (tDCS) has been shown to improve MCI-related memory deficits, but the underlying neural mechanisms remain unclear. This study aimed to investigate which hemodynamic changes are attributable to the individual effects of TC or tDCS, and which alterations arise from their synergistic interaction. Methods In this randomized clinical trial, 128 patients with MCI were assigned to one of four groups: TC combined with tDCS, TC alone, tDCS alone, or health education. Outcome measures included memory scale scores and prefrontal hemodynamic activity assessed using functional near-infrared spectroscopy (fNIRS), measured at baseline and after 12 weeks. Results The combined TC and tDCS intervention produced a significant synergistic interaction effect on verbal memory ( P = 0.032), as well as on changes in oxyhemoglobin (HbO 2 ) concentrations across multiple prefrontal regions. These included the right orbitofrontal cortex during resting state ( P = 0.026); the left dorsolateral prefrontal cortex (DLPFC) during the 0-back ( P = 0.012), 1-back ( P < 0.001), and 2-back tasks ( P = 0.003); the left frontopolar cortex during the 0-back ( P = 0.003), 1-back ( P = 0.008), and 2-back tasks ( P = 0.020); the right frontopolar cortex during the 1-back task ( P = 0.017); and the left ventrolateral prefrontal cortex during the 1-back task ( P = 0.041). Correlation analysis revealed a positive association between changes in HbO 2 concentrations in the left DLPFC during the 1-back task and verbal memory performance. Conclusions TC combined with tDCS may synergistically enhance verbal memory in patients with MCI through modulation of HbO 2 concentrations in the left DLPFC. Trial registration ClinicalTrials.gov Identifier: ChiCTR2200059316