A comparative investigation of transcranial pulsed and direct current stimulation on motor learning and brain oscillation patterns in older adults with mild cognitive impairment: a randomized controlled trial

Age-related declines in motor performance are associated with reduced cortical excitability and impaired neuroplasticity. Noninvasive transcranial electrical stimulation (tES) can improve motor learning, but the comparative efficacy of anodal transcranial direct current stimulation (a‑tDCS) and anodal transcranial pulsed current stimulation (a‑tPCS) in older adults with mild cognitive impairment (MCI) is unclear. This study aimed to compare the effects of a-tDCS and a-tPCS on motor learning and cortical activity in older adults with MCI. Thirty‑nine older adults (age 60–75 years; Montreal Cognitive Assessment (MoCA) 18–23) were randomized to a‑tPCS (n = 13), a‑tDCS (n = 13), or sham (n = 13). Stimulation (2 mA, 20 min) was applied over left M1 during five daily sessions of a Serial Reaction Time Task (SRTT). Behavioral outcomes were reaction time (RT) and error rate (ER). Electroencephalography (EEG) absolute and relative spectral power (theta, alpha, beta), magnitude‑squared coherence (MSC), and imaginary coherence (ICoh) between C3–C4 were measured at baseline, after five intervention sessions, and at two‑week follow‑up. Both a-tPCS and a-tDCS significantly increased alpha and theta spectral power, increased MSC, decreased ICoh, and reduced RT and ER relative to sham (p < .001). a-tPCS produced significantly greater initial changes than a-tDCS in absolute alpha power, relative theta power, alpha and theta MSC, and RT (p < .001). At follow-up, a-tPCS maintained significant changes compared to sham in absolute alpha power, absolute theta power, alpha MSC, and RT (p < .001). In contrast, the effects of a-tDCS showed notable decline over time, with only modest lasting benefits primarily observed in absolute theta and alpha power and beta MSC. Both techniques facilitate motor learning in older adults with MCI, but a‑tPCS caused stronger and more enduring neurophysiological and behavioral effects in this sample. The protocol of this trial was registered at Iranian Registry of Clinical Trials (registration number: IRCT20151228025732N79; July 30, 2023) available at https://irct.behdasht.gov.ir/search/result?query=IRCT20151228025732N79.