This study is a single-center, randomized controlled trial aiming to evaluate the analgesic mechanism of Transcutaneous Electrical Nerve Stimulation based on Wrist-Ankle Acupuncture (TENS-WAA) during unsedated colonoscopy using EEG-fNIRS technology to assess neural activity in brain regions associated with pain perception. Sixty patients aged 18-75 years, with stable cardiopulmonary function and a baseline visual analog scale (VAS) pain score <3, will be enrolled and randomly allocated into the intervention and control groups. The intervention group will receive TENS stimulation based on the Wrist-Ankle Acupuncture theory 10 minutes before the colonoscopy, with a frequency of 2 Hz and adjustable current intensity ranging from 1 to 9 mA. The control group will receive minimal-intensity sham stimulation under identical conditions. All participants will wear EEG-fNIRS devices to monitor neural activity in key pain-related brain areas, including the prefrontal cortex, anterior cingulate cortex, motor cortex, and parietal cortex. Primary outcomes include EEG-fNIRS data, while secondary outcomes are VAS scores at the four colonic bends, colonoscopy duration, and the correlation between EEG-fNIRS signals and pain perception. Statistical analyses will include multivariable linear regression, generalized estimating equations, and mixed-effects models to investigate the analgesic effects and neural mechanisms of TENS-WAA. This study seeks to provide innovative pain management strategies for patients undergoing unsedated colonoscopy and further explore the neuroregulatory potential of TENS-WAA technology.

1. Inclusion Criteria:

   • Patients undergoing unsedated colonoscopy are eligible for inclusion in this study.
   • Aged 18 to 75 years.
   • Meeting the requirements for colonoscopy, with good cardiopulmonary function and stable vital signs.
   • A pre-procedural Visual Analog Scale (VAS) pain score of less than 3.

2. Exclusion Criteria:

   • Participants with speech or cognitive impairments.
   • Those with acute anal or rectal stenosis, acute perianal or rectal infections, acute diverticulitis, or active inflammatory bowel disease.
   • Women who are menstruating, pregnant, or breastfeeding.
   • Patients with active tuberculosis, hemophilia, or advanced malignant tumors.
   • Individuals with sensory disturbances, implanted pacemakers or defibrillators, or ankle skin ulcers.
   • Those who have used sedatives or analgesics either long-term or within the past 24 hours.
   • Individuals with any condition that interferes with EEG-fNIRS signal acquisition, such as cranial abnormalities, implanted metal or electronic devices, epilepsy, or neurological disorders.

De-identified individual participant data (IPD) that will be shared include:

Demographic information (age, sex, colonoscopy history)

Group allocation (TENS-WAA or sham stimulation)

Pain Visual Analogue Scale (VAS) scores at key time points

EEG and fNIRS raw and pre-processed data collected before, during, and after colonoscopy

Procedure duration and event timepoints (e.g., reaching hepatic flexure, splenic flexure, ileocecal valve)

Relevant clinical outcomes (e.g., adverse events, procedure completion status) The data will be available from the corresponding author upon reasonable request, following publication of the main results and with a signed data access agreement. No data that could directly identify individual participants will be shared.

The de-identified individual participant data (IPD) and supporting documents (such as data dictionaries and analysis code) will be available beginning 6 months after publication of the primary results article. Data will remain available for at least 5 years after publication, or longer if required by journal or institutional policy. Requests submitted after this period may be considered at the discretion of the corresponding author and study team.

Researchers from academic institutions, hospitals, or other recognized research organizations may access the de-identified individual participant data (IPD) and supporting documents (such as data dictionary and analysis code) for legitimate scientific research purposes by sending an email request to the corresponding author. The request should briefly describe the intended research use. All requests will be reviewed by the study team to ensure ethical compliance. Data sharing will require a signed data access agreement. Only de-identified data will be shared; no information that could directly identify participants will be provided.

Before the trial begins, envelopes containing sequentially numbered cards from 1 to 60 will be prepared to determine participant allocation. The coordinator will open the envelopes in the order of participant enrollment. Throughout the trial, researchers are not allowed to alter the enrollment sequence. Participants will be informed in advance that they may experience electrical stimulation sensations, and communication between participants will be prohibited during the entire trial process. The statistician responsible for data analysis will remain blinded to the group allocation of participants.