Neural Mechanisms of Light Driven Analgesia
University of North Carolina, Chapel Hill
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.
Description
The investigators will recruit 30 participants with chronic musculoskeletal pain (cMSP) and 30 healthy, matched controls. Participants will undergo a comprehensive assessment of important covariates that influence pain experience. Individuals will then undergo quantitative sensory testing that will be used to psychophysically assess pain sensitivity and conditioned pain modulation (CPM) immediately prior to the scanning session. Individuals will then undergo fitting of a rapid inflation pressure cuff on the left calf to achieve the same level of pain among each participant (who may have differ…
Eligibility
- Age range
- 18+ years
- Sex
- All
- Healthy volunteers
- Yes
Inclusion Criteria for participants with cMSP and healthy controls (n=30) * 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. Inclusion Criteria for participants with cMSP only (n=30) * To be eligible, participants must have a score of ≥7 on the Widespread pain index (WPI) and ≥5 on the…
Interventions
- OtherS-cone modulating visual stimulus
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.
- OtherEqual Energy White Visual Stimulus
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.
- OtherGreen light visual stimulus (S-OFF)
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.
- OtherEvoked Pressure Pain Stimulus
Location
- University of North Carolina at Chapel HillChapel Hill, North Carolina