Investigating the Transcutaneous vs. Transcranial Mechanisms of Trigeminal Nerve Stimulation (eTNS) Using fMRI

Condition(s) studied

Investigational drug(s) / intervention(s)

Topical Lidocaine: Application of a local anesthetic over the forehead targeting the supraorbital nerve branch prior to the MRI scan, intended to block peripheral transcutaneous nerve conduction.

Direct Current eTNS (DC-eTNS): Active direct current electrical stimulation applied via electrodes on the forehead. The stimulation is synchronized with a 7-minute and 30-second BOLD fMRI sequence, which includes a 15-second current ramp-up phase at the beginning and a 15-second current ramp-down phase at the end.

Sham DC-eTNS: An inactive or sensory-matched sham stimulation administered during a 7-minute and 30-second BOLD fMRI sequence to serve as a baseline comparator.

Study summary

Transcutaneous Trigeminal Nerve Stimulation (eTNS) is a non-invasive technique that modulates brain activity by applying electrical currents to the forehead. However, it remains unclear whether its effects are primarily driven by activating peripheral nerves in the skin (the transcutaneous pathway) or by the electrical current passing directly through the skull into the brain (the transcranial pathway).

This study aims to differentiate these two mechanisms in healthy volunteers. Participants will complete two separate MRI scanning sessions. In one session, a local anesthetic (lidocaine) will be applied to numb the skin over the forehead (specifically the supraorbital nerve branch) to temporarily block the peripheral nerve signals. In the other session, no anesthesia will be used. During both sessions, participants will receive active direct current eTNS (DC-eTNS) and a sham (inactive) stimulation while inside a 3T MRI scanner.

Researchers will simultaneously measure brain activity (fMRI) and physiological signals (breathing and heart rate). By comparing the brain and bodily responses between the anesthetized and non-anesthetized conditions, the study seeks to determine exactly how eTNS signals travel to and affect the brainstem, cortex, and autonomic nervous system.

Eligibility

Primary outcome measure(s)

• Amplitude of Low-Frequency Fluctuations (ALFF) in the Brainstem — Computed from the data acquired during the 7-minute and 30-second fMRI scan for each stimulation condition.
  The primary neuroimaging metric is the ALFF of the BOLD signal, specifically targeting the brainstem regions that encompass the primary nodes of the trigeminal nerve. To differentiate the transcutaneous and transcranial mechanisms, the core statistical analysis will evaluate the interaction effect by comparing the ALFF contrast of (DC-eTNS minus Sham) in the No-Anesthesia condition against the contrast of (DC-eTNS minus Sham) in the Anesthesia (Lidocaine) condition.

Trial sites (1)

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