A single-session randomised crossover fNIRS study comparing three upper-limb mirror therapy task paradigms in healthy adults: a study protocol

Background

Mirror therapy (MT)—specifically paradigms using mirror visual feedback (MVF)—is widely used in neurorehabilitation; however, mechanistic implementations vary substantially in movement content, rhythmicity and attentional demands. This protocol describes an acute mechanistic, within-participant fNIRS screening study designed to compare three prespecified upper-limb mirror-therapy task paradigms and to quantify associated subjective experience after each condition in healthy adults during a single visit.

Methods and analysis

This is a single-centre, within-participant, randomised crossover study conducted at Wuhan Wuchang Hospital (Wuhan, China). Healthy adults aged 18–35 years will complete three task conditions once each in a counterbalanced order using a 3×3 Latin-square scheme: UMT1 (task-oriented rhythmic functional movement), UMT2 (open-ended free movement with auditory control), and UMT3 (non-functional rhythmic movement). fNIRS will be acquired using the NirSmart-6000A system during a standardised block design. The primary outcome is ROI-level HbO activation quantified as GLM-derived β estimates within the prespecified primary ROIs (bilateral SM1/M1 and bilateral PMC). Secondary outcomes include ROI-level windowed ΔHbO (5–20 s post-onset relative to the immediately preceding rest; descriptive only), ROI-level ΔHbR, and post-condition subjective ratings (illusion, immersion, confusion and fatigue; 1–7 Likert). Condition effects will be analysed using linear mixed-effects models with fixed effects for condition and period and prespecified multiplicity-adjusted pairwise contrasts.

Ethics and dissemination

Ethics approval was obtained from the Ethics Committee of Wuchang Hospital Affiliated to Wuhan University of Science and Technology (Approval No.: 2025-112-01; approved on 2025-08-21). The study is expected to be minimal risk. Findings will be disseminated through publication of this protocol manuscript and subsequent results manuscripts and conference presentations.

Trial registration number

Chinese Clinical Trial Registry (ChiCTR2600116634). This study is conducted as a prespecified mechanistic sub-study under the overarching registered project.

Strengths and limitations of this study

• Within-participant randomised crossover design reduces between-participant variability for mechanistic comparisons.

• Prespecified task timing, ROIs, contrasts and multiplicity control reduce analytic flexibility.

• Latin-square counterbalancing and modelling of period effects mitigate systematic sequence bias.

• Healthy-participant, single-session design limits direct generalisability to clinical stroke populations and long-term treatment effects.

• fNIRS remains sensitive to motion and scalp–optode coupling; residual artefacts may persist despite prespecified QC and preprocessing.