Name: FMRI Participant Preparation and Visual Cortex Scanning
Uploaded: 2023-12-08T12:40:00
Description: Watch this Scientific Journal Video about FMRI Participant Preparation and Visual Cortex Scanning at JoVE.com

fmri participant preparation and visual cortex scanning

Advancing Visual Cortex Mapping for Enhanced Evaluation of Vision Disorders

Functional magnetic resonance imaging (fMRI) is a valuable method to assess changes in regional neurovascular function within the visual cortex in response to stimuli, as changes in regional blood flow correlate to the activation of brain regions1,2. High-resolution retinotopic blood oxygenation level-dependent (BOLD) signal measurements represent changes in deoxyhemoglobin, which are driven by localized changes in blood flow and blood oxygenation within the brain1,2. BOLD activity patterns collected from fMRI data can be used to functionally map the peripheral and central visual cortex, as well as detect changes in the retinotopic map in response to visual impairment and neurodegeneration3.
Most previous fMRI studies made use of narrow-view (around &#177;12&#176; of the central visual field) non-retinotopic stimuli or simple retinotopic stimuli with narrow-view visual stimuli, which provided limited functional parcellation of the retinotopic representation in the visual cortex and limited assessment to only the central visual field, excluding the periphery3. Consequently, narrow-view fMRI data has reported inconsistent BOLD percent changes in glaucoma patients4,5,6. There is therefore a need for improved fMRI approaches to assessing the peripheral and central visual field, particularly in the evaluation of diseases such as glaucoma.
Glaucoma is the leading cause of irreversible blindness, affecting 10% of people by the age of 807. Glaucoma is caused by the progressive, irreversible neurodegeneration of retinal ganglion cells, which are responsible for transmitting visual stimuli to the brain through the optic nerve. In primary open-angle glaucoma (POAG), the most common form of glaucoma, increased intraocular pressure causes thinning of the retinal nerve fiber layer (RNFL), leading to the loss of peripheral vision followed by peripheral and central blindess8,9,10,11. Histological evidence from animal studies suggests that glaucoma additionally results in progressive neurodegeneration of the optic nerve, optic tract, lateral geniculate nucleus, optic radiation, and visual cortex12,13. MRI technology offers a minimally invasive method of assessing both blood oxygenation and neurodegeneration in the visual cortex. In patients with glaucoma, MRI has found evidence of gray-matter atrophy in the visual pathway13,14,15,16 and abnormal white matter in the optic chiasm, optic tract, and optic radiation1,17,18.
To further explore the effects on visual processing, fMRI can be used to detect brain function in response to visual cues. The protocol herein describes a novel method to obtain a low-cost, wide-view retinotopic map using high-resolution retinotopy fMRI with wide-field (&#62;100&#176;) stimuli, as described by Zhou et al3. Visual stimuli of expanding rings and rotating wedges were used to elicit retinotopic mapping of the eccentricity and polar angle for fMRI. BOLD fMRI percent changes were analyzed as a function of eccentricity to evaluate brain function, corresponding to both central and peripheral vision. The BOLD fMRI percent change may be used to visualize activation throughout the visual cortex. These fMRI measures provide a reliable new method to evaluate neurodegenerative changes and their functional effects on the visual cortex found in eye diseases involving visual field defects, such as glaucoma.

Author Spotlight: Insights into Visual Cortex Research Through Wide-View fMRI Mapping 

Functional Magnetic Resonance Imaging (fMRI) of the Visual Cortex with Wide-View Retinotopic Stimulation

This research focuses on providing a practical, cost-effective visual presentation system to evaluate changes in the visual cortex due to ophthalmic diseases. We provide a method to create a wide viewing angle, retina atopic map, using FMRI to assess the functional activity of the visual cortex. A current experimental challenge is that standard systems for presenting visual stimuli for FMRI only cover small area of the visual fields, and with the view partially obstructed by the head coil.This protocol provides method for wide view and unobstructed stimuli that balances cost, efficacy, and precision. Our protocol provides an affordable, moderately wide view of up to a hundred degrees of the visual field. Compared to other techniques, it avoids distortions, additional costs for projector lenses or fiber optic bundles, and other complexities, such as the need for contact lenses.Our findings can be used to expand the understanding of the visual cortex, enabling the mapping of peripheral and central regions via an affordable, wide view FMRI system. This could enhance the management of visual impairments in eye diseases such as glaucoma, which involves dysfunction of the visual system in the brain.

Watch this Scientific Journal Video about FMRI Participant Preparation and Visual Cortex Scanning at JoVE.com

FMRI Participant Preparation and Visual Cortex Scanning  

fMRI Participant Preparation and Visual Cortex Scanning

Begin by instructing the participant to fixate on the central cross during the imaging scans. Briefly demonstrate the visual stimulation to familiarize the participant with the procedure. Position the participant comfortably on the scanner table and immobilize the participant's head in the posterior half of the head coil array with foam padding to reduce motion artifacts.Provide ear plugs to protect their hearing. Use the scanner's positioning system to move the table into the scanner bore. Place the wide-view mirror 10 centimeters from the participant's eyes.Adjust the mirror to maintain a consistent viewing angle. Begin fMRI scanning with a localizer scan, incorporating three orthogonal planes and adjusting the scanner for frequency and shimming calibration. Proceed with an MP-RAGE anatomical scan for enhanced EPI slice positioning.At the start of the fMRI protocol, instruct the participant to fixate on the white cross atop a gray background at the stimuli's center for 10 seconds. Create visual stimuli using a compatible program by displaying a series of rotating wedges for 30 seconds. The wedges should extend to the edge of the screen or mirror with an eight-hertz contrast-reversing black and white checkerboard pattern.Present the white cross for an additional 10 seconds. Repeat cross fixation and stimulation display with the second 30-second visual stimulation paradigm, consisting of expanding and contracting rings. Maintain an eight-hertz contrast-reversing black and white checkerboard pattern at 100%contrast during the experiment.Upon completion of imaging, slide the table out of the scanner bore, ensuring the participant remains still. Next, remove the screen and then remove the mirror before placing the anterior portion of the head coil. Position the table back into the center of the scanner.Acquire a quick localizer scan to account for any movement, followed by an MP-RAGE scan using the full head coil. The polar maps revealed no obvious differences between the primary open-angle glaucoma participants and healthy participants. The eccentricity maps showed that the central region of the parafovea that was activated by the smaller ring stimuli appeared larger in the primary open-angle Glaucoma patient.BOLD percent changes at different eccentricities were reduced in primary open-angle glaucoma patients, especially at more peripheral eccentricities. The BOLD changes were significantly reduced between the two groups, more so at larger eccentricities. The BOLD percent changes averaged for central vision were only slightly and not significantly reduced in primary open-angle glaucoma patients, while the changes were significantly reduced for peripheral vision.

Research

JoVE Journal

Neuroscience

High-resolution retinotopic blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) with a wide-view presentation can be ...