Personalized assessment of high-definition slow-oscillatory transcranial direct current stimulation (so-tDCS) in older adults with sleep and subjective cognitive complaints: A study protocol for a randomized clinical trial

BACKGROUND: Subjective cognitive decline (SCD) is increasingly recognized as an early and potentially modifiable stage in the trajectory of neurodegenerative diseases. In older adults with SCD, untreated sleep disturbances may accelerate the neurodegenerative process, potentially via mechanisms involving amyloid-beta accumulation, and contribute to more rapid cognitive deterioration. Currently, non-pharmacological treatment options that concurrently manage SCD and sleep disturbances remain scarce. High-definition slow-oscillatory transcranial direct current stimulation (so-tDCS) is an emerging, frequency-specific neuromodulation technique designed to enhance brain health and cognition. METHODS AND DESIGN: This is a randomized, double-blind, sham-controlled clinical trial. Right-handed Chinese older adults with SCD and sleep disturbances will be randomly assigned to receive either high-definition 0.75 Hz so-tDCS or sham stimulation over a 4-week intervention period, with 40 participants per group. Outcome measures, including galvanic skin response, subjective cognitive complaints, sleep quality, salivary amyloid-beta levels, and domain-specific cognitive performance, will be evaluated at four time points: baseline, week 4 (immediately post‑intervention), and follow‑up at weeks 8 and 12. CONCLUSIONS: Personalized neurophysiological signals, namely electrode-skin impedance, will be monitored using state-of-the-art measurement during so-tDCS. The successful implement of this signal will provide researchers with access to an "add-on" setting that enables them to easily, quickly and quantitatively evaluate real-time neurophysiological signals, thereby facilitating the incorporation of transcranial brain stimulation into clinical practice. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT07433738.