Neural Mechanisms of Light Driven Analgesia
University of North Carolina, Chapel Hill
60 participants
Feb 1, 2026
INTERVENTIONAL
Conditions
Summary
The goal of this study will be to understand the biological mechanisms that are responsible to light-driven analgesia. Light presented to the retina has been shown to have pain relieving properties in pre-clinical and clinical studies. In this study the investigators will evaluate the functional connectivity between subcortical visual areas and non-image forming brain areas that are involved in pain sensation. The investigators will also evaluate how three colored light stimuli presented to the retina results in changes in whole brain evoked activation patterns in participants with chronic musculoskeletal pain and in healthy controls. The investigators will also assess while brain evoked activation patterns in response to a pressure pain stimulus in the presence of three light stimuli in individuals with chronic musculoskeletal pain and healthy controls.
Eligibility
Inclusion Criteria11
- Adults ≥18 years of age.
- Individuals who do not have any plans for medication or treatment changes for the next 3 months.
- Participants must be willing and able to undergo an MRI.
- Participants must not be claustrophobic
- Participants must be alert and oriented and able to provide informed consent.
- Individuals must be able to speak and read English.
- To be eligible, participants must have a score of ≥7 on the Widespread pain index (WPI) and ≥5 on the symptom severity scale (SSS), or 4-6 on the WPI and ≥9 on the SSS in the 2016 Fibromyalgia Questionnaire.
- Pain symptoms must have been present for 3 months or longer.
- Pain must be present in 4 out of 5 body regions.
- Individuals enrolled will have an average pain severity ≥4 on the 0-10 NRS over the month prior to enrollment to recruit individuals with moderate to severe chronic MSP.
- additional participants without chronic MSP will be recruited with diagnosed congenital stationary night blindness
Exclusion Criteria7
- Presence of retinal vision disorders or conditions resulting in vision impairment.
- Patient-reported photosensitivity, photophobia, or aversion (as may occur in autoimmune diseases such as systematic lupus erythematosus).
- Disorders including uveitis, cataracts, color-blindness, history of seizure disorder.
- Plans for analgesic treatment plan changes in next 3 months (surgery, analgesic medication changes, injections, pain procedures, etc).
- Prisoner Status.
- Pregnancy.
- Contraindications to MRI imaging. These include the presence of implanted/embedded ferromagnetic materials, implanted medical devices that are not MRI compatible, and claustrophobia.
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Interventions
The investigators will deliver a uniform wide-field, S-cone modulating stimulus via a fiberoptic, MRI-safe visual stimulator. This stimulus approximates the appearance of white but modulates the S-cone, driving the S-ON and S-OFF pathways by alternating two lights at 19 Hz using a mixture of light emitting diodes (LEDs), including those embedded in our stimulus with spectral peaks of 405, 565, and 660 nm. This stimulus will differentially activate the S-cones where, between the two phases the ratio of S-cone activity is 100. The frequency alternating between the two lights, 19 Hz, was chosen because retinal ganglion cells in the retina still respond robustly but above the cortical perceptual flicker detection threshold.
The investigators will deliver a uniform wide-field, equal-energy light stimulus via a fiberoptic, MRI-safe visual stimulator. This will serve as a reference condition in which chromatic opponency has been eliminated. This stimulus ensures that the quantal catch of each cone photoreceptor (S-, M- and L-) is held constant using a mixture of LEDs, including those embedded in our stimulus with spectral peaks of 405, 565, and 660 nm.
The investigators will deliver a uniform wide-field, green light modulating stimulus via a fiberoptic, MRI-safe visual stimulator. Static Green (565 nm) Light presented via MRI compatible light guides.
The pressure in which a rapid inflation cuff positioned over the left gastrocnemius achieves a pain severity of 40 where 0 is "no pain" and 100 is the "worst pain imaginable will be determined pre-scan and applied during the entire functional imaging acquisition to evoke a deep pressure pain.
Locations(1)
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NCT07245303