Topography of Cortical Activation with Mirror Visual Feedback and Electromyography-Triggered Electrical Stimulation: A Functional Near-Infrared Spectroscopy Study in Healthy Older Adults

Background/Objectives: Mirror visual feedback (MVF) can facilitate post-stroke upper limb recovery. Pairing MVF with electromyography-triggered electrical stimulation (ES) may enhance afferent input and sensorimotor engagement. As aging alters neurovascular responses, we aimed to test MVF and MVF + ES in older adults using functional near-infrared spectroscopy (fNIRS). Methods: Seventeen right-handed adults performed left wrist flexion under three visual conditions—circle fixation (CT), viewing the right hand (RT), and mirror viewing (MT)—each with/without ES to right wrist flexors synchronized to left forearm electromy-ography (EMG). Oxygenated hemoglobin (oxy-Hb) was recorded over the bilateral inferior frontal gyrus (IFG), precentral gyrus (PrG), postcentral gyrus (PoG), supramarginal gyrus (SMG), superior parietal lobule (SPL), and supplementary motor area. A 2 × 3 repeat-ed-measures analysis of variance (ES × visual), with Bonferroni-corrected post hoc tests, assessed effects. The left forearm EMG verified comparable efforts. Results: ES increased oxy-Hb levels in the left IFG, PrG, PoG, and SMG, with a significant ES × visual interaction in the left IFG. Post hoc tests revealed the following: MT + ES > MT (left IFG), RT + ES > RT (left PoG, SMG), and CT + ES > CT (left PoG, PrG, SMG, SPL). The right IFG/PrG ratio was higher for CT + ES than for CT. The left EMG did not differ. Conclusions: In older adults, MVF + EMG-triggered ES augments left-lateralized frontopa-rietal/sensorimotor activation beyond MVF alone, with augmentation topography de-pending on the visual context. These findings support neurophysiological plausibility and warrant dose–response and behavioral transfer studies in stroke cohorts.