Screening sham mirror-therapy materials using fNIRS: protocol for an acute within-participant randomised crossover mechanistic study

Introduction

Selecting an appropriate sham control is a key challenge in trials of mirror therapy—specifically paradigms using mirror visual feedback (MVF), because visually similar control conditions may still elicit mirror-related cortical responses. This protocol describes an acute mechanistic, within-participant fNIRS screening study designed to identify the sham mirror-therapy material condition with the most “neutral” neural signature relative to true MVF during a single exposure.

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 four conditions in one visit: C1 true MVF and three prespecified sham-material conditions (C2–C4), with condition order counterbalanced using a Latin-square schedule. fNIRS will be acquired during a standardised grasping task. Online acquisition-time quality control (SCI and CV thresholds) will be applied with prespecified re-acquisition rules. The primary outcome is ROI-level task-evoked change in oxygenated haemoglobin (ΔHbO) within prespecified ROIs (PMC and SM1/M1), estimated primarily using GLM-derived β estimates. Condition effects will be analysed using linear mixed-effects models with prespecified contrasts and Holm multiplicity adjustment to rank sham conditions by a prespecified neutrality decision rule.

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). Findings will be disseminated through publication of this protocol manuscript and a subsequent results manuscript, with key supplementary materials provided as online appendices/supplements as required by the target journal.

Trial registration number

Chinese Clinical Trial Registry (ChiCTR2600116634).

Strengths and limitations of this study

Within-participant randomised crossover design reduces between-participant variability and is well suited for acute mechanistic screening of sham conditions.

Prespecified sham conditions and neutral-ranking decision rule (including prespecified ROIs, contrasts, and Holm multiplicity control) help limit analytic flexibility and support transparent interpretation.

Operational reproducibility safeguards are specified, including standardised task timing/instructions, acquisition-time QC thresholds (SCI/CV) with re-acquisition rules, and frozen channel-to-ROI mapping and material-definition records in the Supplementary materials.

Single-centre, healthy-participant, single-session paradigm may limit generalisability to clinical stroke populations and to longer-term therapeutic effects.

Blinding may be imperfect because perceptual differences between materials can affect expectancy/attention; blinding assessment is included but residual bias is possible.

fNIRS is susceptible to motion/scalp-coupling variability and physiological noise ; despite prespecified QC and preprocessing, residual artefacts may remain and can reduce sensitivity.