This work was supported by the National Institutes of Health [R01EY030996].

Research with human participants was performed in compliance with institutional guidelines at the University of Texas Health Science Center and Stony Brook University, with informed consent obtained from participants for these studies and use of their data.
1. Setup of MRI scanner and imaging protocols
<ol>
	<li>For fMRI, use a 3T MRI scanner with multi-channel receiver head coils. Different field strengths can also be used but may present difficulties with signal-to-noise ratio (SNR) or distortion artifacts, so adjust accordingly. Use only the posterior half of the head coil for fMRI to allow for a larger viewing angle unobstructed by the anterior half of the coil.</li>
	<li>Set up a T1-weighted magnetization-prepared rapid acquisition gradient echo (MP-RAGE) sequence with a repetition time (TR) of 2.2 s, echo time (TE) of 2.8 ms, field of view (FOV) of 176 mm x 256 mm x 208 mm, spatial resolution of 1 mm x 1 mm x 1 mm, bandwidth of 190 Hz/pixel, flip angle of 13&#176;, and a scan duration of 3.1 min3.</li>
	<li>Set up a gradient-echo, echo-planar imaging (EPI) sequence with a TR of 2 s, TE of 30 ms, FOV of 220 mm x 220 mm, in-plane resolution of 1.7 mm x 1.7 mm, 29 slices with a thickness of 3 mm, and a bandwidth of 1,500 Hz/pixel3.</li>
	<li>Measure the dimensions of the head coil and scanner bore, and then construct a simple frame by cutting a polyvinyl chloride (PVC) pipe into suitable lengths and connecting them with PVC elbows. Obtain a mirror that is at least 25 cm wide and 15 cm tall and attach it to a plastic rod with screws (small holes can be drilled into the mirror).
	<ol>
		<li>Attach the ends of the plastic rod to the PVC frame with nylon screws (Figure 1A). Make sure that the nylon screws are slightly loose to allow the mirror to be rotated by hand to optimize the angle for each participant.</li>
	</ol>
	</li>
	<li>Make a screen to go inside the MRI bore. Cut a segment of a rear-projection screen that is approximately the size of the MRI bore. Construct a frame that is the size of the bore and attach the screen to the frame with screws. Place the screen inside the scanner just behind the head coil to minimize the distance between the screen and mirror and maximize the FOV. 
	NOTE: If the scanner bore is large enough, a single screen can be used for the participant to view directly instead of the mirror and rear projection screen setup. A projection screen attached to a thin sheet of wood for backing or a sheet of thin matte white plastic can be used as a screen and placed on the frame instead of a mirror. The projector should then be positioned and focused, such that it fills the screen and is in focus.</li>
</ol>
2. Participant preparation
<ol>
	<li>Inform the participant about the procedure, risks, and benefits of the fMRI scan. Obtain their informed consent.</li>
	<li>Ensure that the participant does not have any contraindications to MRI. This includes screening for pacemakers, metal implants, or claustrophobia. If you have any uncertainty, consult with a qualified radiologist or researcher, and exclude the participant from the study if any uncertainty remains.</li>
	<li>Explain the visual stimulation protocol and the need for the participants to fixate on the central cross during the fMRI scans. Show the participant a short demonstration of the visual stimulation for instructional purposes to familiarize them with the procedure.</li>
	<li>Carefully position the participant on the table of the MRI scanner to ensure that they are comfortable and relaxed. Provide earplugs and/or a sound-dampening headset to reduce the acoustic noise the participant will hear to protect their hearing.</li>
	<li>Immobilize the participant&#39;s head in the posterior half of the head coil array, using foam padding on the sides of the head to ensure that the head is properly immobilized to reduce motion artifacts. Use the scanner&#39;s positioning system and move the table into the scanner bore.</li>
	<li>Place the wide-view screen or mirror 10 cm from the patient&#39;s eyes (Figure 1B). Place the bore-sized screen from the back of the scanner bore just behind the head coil. Adjust the position and angle of the mirror/screen for each participant to achieve a consistent viewing angle.</li>
	<li>Ensure that the participant is comfortable throughout the scan via communication through the intercom.</li>
</ol>
3. fMRI scanning of participant
<ol>
	<li>Run a localizer scan with three orthogonal planes and scanner adjustments and calibrations for frequency adjustment and shimming.</li>
	<li>Run an MP-RAGE anatomical scan to help position the EPI slices.</li>
	<li>Create visual stimuli, as described in the following steps, using a program for running behavioral or psychological experiments.</li>
	<li>At the start of the fMRI protocol, instruct the participant to fixate on the white cross (3&#176; x 3&#176;), which should be on top of a gray background at the center of the stimuli for 10 s. 
	NOTE: The white cross will be shown before and after each visual stimulation paradigm for 10 s. Thus, the total fMRI stimulation test for each paradigm is 200 s.</li>
	<li>Present the first visual stimulation paradigm (a series of rotating wedges) for a period of 30 s (giving an angular velocity of 6&#176;/s) and cycle through six periods. The wedge stimuli should include 12 frames of rotating wedges (one scan with clockwise rotation and one with counterclockwise), extending to the edge of the screen/mirror (&#62;100&#176; visual field), with an 8 Hz contrast-reversing black and white (100% contrast) checkerboard pattern (Figure 2A).</li>
	<li>Present the white cross once again for 10 s.</li>
	<li>Repeat steps 3.4-3.6 with the second visual stimulation paradigm (a series of expanding and contracting rings) for a period of 30 s (expanding or contracting at 1.8&#176;/s of the visual field) and cycle through six periods. The ring stimuli should include eight frames of expanding or contracting rings (&#62;100&#176; visual field), with an 8 Hz contrast-reversing black and white (100% contrast) checkerboard pattern (Figure 2B).</li>
	<li>After completing the fMRI, move the table out of the scanner bore while instructing the participant to remain still. Remove the mirror/screen, place the anterior portion of the head coil in addition to the posterior, and move the table back into the center of the scanner.</li>
	<li>Acquire a quick localizer scan in case of any movement and acquire an MP-RAGE scan with the full head coil. 
	NOTE: An anatomical image with the whole head coil is needed for accurate registration for group analyses and reconstruction purposes.</li>
</ol>
4. Analysis of retinotopic fMRI data
<ol>
	<li>Download and install the FreeSurfer application for MRI analysis (https://surfer.nmr.mgh.harvard.edu)20. 
	NOTE: FreeSurfer version 5.3.0 was used herein.</li>
	<li>Obtain images in Digital Imaging and Communications in Medicine (DICOM) format from the MRI scanner. Convert the DICOM files to nifti format using the dcm2niix application (https://www.nitrc.org/projects/mricrogl)21.</li>
	<li>Process the T1-weighted scan to provide a cortical surface reference, as described in the following two steps. Use FreeSurfer to convert structural data from nifti format to .mgz format (mri_convert command).</li>
	<li>Use the recon-all command in a shell environment to perform automated segmentation and cortical reconstruction of the structural data. 
	NOTE: This step can take over 20 h to complete.</li>
	<li>Use the graphical user interface tksurfer to view the inflated hemisphere and virtually cut the visual cortex along the calcarine fissure, and select the occipital lobe. Use the mris_flatten command to flatten the visual cortex patch. Repeat this step for both hemispheres.</li>
	<li>For the fMRI data, first remove the rest periods, with only the fixation cross presented, from the start and end of the data. Screen the fMRI data for artifacts or large movements.</li>
	<li>Preprocess the functional data for spatial smoothing and motion correction. Model the retinotopic stimulus paradigm and apply a canonical hemodynamic response function to construct the response function.</li>
	<li>Perform retinotopic phase-encoded analysis of the fMRI data using the FreeSurfer functional analysis stream (mkanalysis-sess, selxavg3-sess, and fieldsign-sess commands) to correlate the BOLD fMRI time series with a modeled response function and obtain phase-encoded retinotopic maps, with a significance level of p &#60; 0.01 (Figure 3).</li>
	<li>Visualize the results of the retinotopic maps with color-coded activation maps overlaid on the virtually flattened visual cortex using the tksurfer-sess command, and display using the rtview command.</li>
	<li>Use the phase-encoded retinotopic maps from the wedge stimuli to help define the boundaries of the primary visual cortex (V1) and other extra striate areas (V2 and V3) by field sign maps (Figure 3A), along with anatomical landmarks and FreeSurfer atlases.</li>
	<li>To calculate the BOLD response at different eccentricities, first use FSL Feat (http://fsl.fmrib.ox.ac.uk/fsl) to calculate statistical maps using a general linear model for each size of ring stimuli with a z-score threshold of Z &#62; 2.322,23. If group analysis is being performed, calculate the second level analysis for statistical maps of group differences with FSL Feat to help determine the BOLD response at different eccentricities.</li>
	<li>Co-register the fMRI images onto the reconstructed cortical surface using the FreeSurfer bbregister and tkregister2 commands to align the participant&#39;s fMRI data to the anatomical structural image of their brain and ensure accurate spatial alignment.</li>
	<li>Group the ring stimuli by eccentricity for each of the eight frames. Manually draw regions of interest for different eccentricities based on the activated voxel regions for each frame. Take the BOLD percent changes and plot them as a function of eccentricity. Also, bin the eccentricity data into central (&#60; &#177;12&#176;) and peripheral (&#62; &#177;12&#176;) regions, where a &#177;12&#176; visual stimulus is typical for retinotopic fMRI studies.</li>
</ol>

Advancing Visual Cortex Mapping for Enhanced Evaluation of Vision Disorders

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The authors have nothing to disclose.

The above protocol for utilization of wide-view retinotopic fMRI is an innovative method to evaluate the effects of vision loss and eye diseases on the brain. Through wide-field retinotopic mapping of the visual cortex with the use of a wider-view screen, this approach allows for a more comprehensive understanding of the visual system's functional organization. This could lead to a better understanding of abnormalities in the brain's visual processing system, which occurs in neurodegeneration, such as in glaucoma24,25. This technology can also be used to detect and analyze brain degeneration and reorganization in other conditions that cause blindness, such as age-related macular degeneration26,27. 
A single human eye has about a 100&#176; visual angle. Previous techniques used in most visual fMRI studies used a FOV of less than 30&#176;, limiting the portion of the visual cortex that could be activated and analyzed by the fMRI28. Consequently, peripheral vision could not be visualized, forcing all analyses to be focused solely on the central visual field. Clinically, this prevented clinicians from accurately performing preoperative cortical mapping, crucial for avoiding vital locations when performing brain surgeries29. With the wide-view retinotopic fMRI technique described in this protocol, the visual angle has been increased to up to 100&#176; (&plusmn;50&#176;)3,30,31. To allow for a wide-view image and decrease visual obstruction caused by the head coil, only the posterior half of the head coil is used. Head coils usually have a relatively small window, with bars across that impede the ability to fully see the wide-view retinotopic stimuli. However, using only the posterior portion of the head coil causes large signal inhomogeneity across the brain and reduces the SNR in the anterior and central regions. The image quality and SNR of the posterior occipital lobe should not be heavily impacted32. However, the exact effects of using only the posterior portion of the coil likely depend on a specific coil design (number and size of arrayed coils), so testing the SNR or signal-to-noise fluctuation ratio in a few subjects with and without the anterior portion can be done if there is a concern of significant SNR loss with a given coil32. 
Proper setup of the T1-weighted MP-RAGE sequence is essential to properly register functional images to high-resolution brain structural images and for anatomical registration to templates or for group studies. As such, we acquire the T1-weighted image using the entire head coil, which may result in slight movement of the participant relative to the fMRI scan. Alignment of the fMRI to the anatomical scan is a routine analysis step, so this should not be an issue. Alternatively, the acquisition of the T1-weighted image without the anterior coil could be done, but the image inhomogeneity may impact the quality of registration to a reference template. To avoid motion artifacts, it is crucial to properly immobilize the participant's head within the head coil. Motion artifacts can naturally occur without proper stabilization, which will negatively affect the quality of the fMRI data collected, leading to poorer results from the analysis. While post-processing motion correction is routine for fMRI analysis, large movements can still impact the results, so it is important to check functional scans for data quality and discard studies with major artifacts. In this protocol, participants were instructed to focus on a white cross for 10 s, both before and after each visual stimulation paradigm, to obtain baseline BOLD data. This helped reduce the variability of the fMRI at baseline, and also allowed the subject's brain to adjust to the scanner sounds and background screen brightness before the actual visual data tests began. 
There are a variety of alternative approaches that could be considered for wide-view fMRI. The approach described herein, using a large screen/mirror with only the posterior half of the head coil, can provide a moderate wide-view up to around a 100&#176; FOV3,30. The cost to make the mirror/screen is very low (potentially &lt;US $100), assuming a standard projector is already available. Greco et al. used a slightly different approach, with the screen placed after the mirror in the optical path, directly in front of the subject's face (7.5 cm away), providing an 80&#176; visual angle28. MR-compatible glasses were needed for the participant to be able to focus on the screen. Ellis et al. also used a similar approach, but with the projector tilted down onto a mirror on the bottom of the bore, which reflected the stimuli directly onto the top of the bore above the subject's face, providing a 115&#176; visual angle32. The view is distorted by the curved bore, which requires the images for the stimuli to be warped to correct. An extension of this approach was recently reported with a custom curved screen at the top of the scanner bore and two mirrors that were able to provide an ultra-wide FOV of 175&#176;34. Some of these reported methods used the anterior portion of the head coil and others did not; however, any of these methods could be used either way, with potentially a slightly higher SNR using the anterior coil, but with the tradeoff of reduced visual angle and portions of the visual field being blocked. A potential limitation with all methods using a projector is that, for a screen with custom size and location, the projector has to be adjusted for the focus and size of the projected image by adjusting the projector/lens, moving the projector, or getting custom lenses if the previous methods are not sufficient. 
Another approach used a transparent plastic rod with a curved end as the screen, with a projector to provide a slightly larger visual angle of 120&#176;, which is compatible with using the anterior head coil without limiting the FOV. However, only monocular stimulation can be performed. A special lens for the projector is needed, which increases the cost, and contact lenses must be worn for the participant to be able to focus on the screen, which complicates the setup31. A similar approach used fiber-optic bundles to directly transmit and present images from a screen to a participant's eye, which provided a visual angle of up to 120&#176;33. Contact lenses must also be worn, and only a single eye could be stimulated at a time. This method requires a long and high-density fiber optic bundle, which can have relatively low resolution for the presentation and may be moderately expensive33. 
Visual impairment and eye disease can affect the structure and function of the visual cortex. BOLD fMRI can be used to visualize retinotopic cortical function, but most visual presentation systems used for fMRI only stimulate the central visual field. This protocol describes the implementation of a wide-view presentation system for fMRI that can be used to functionally map the peripheral and central visual cortex. This system can be set up easily and at a low cost utilizing common MR-compatible projectors. Although with some limitations, the protocol described has the potential to analyze functions of the visual cortex corresponding to central and peripheral vision at a level that balances cost and precision. The data collected through this method can be analyzed to determine selective activation based on different types of visual stimuli and brain communication amongst different areas for visual processing. This method could be used to evaluate changes in the function of peripheral and central visual cortex due to vision loss and eye diseases such as glaucoma. This technology therefore has applications in the diagnosis, management, and treatment of eye diseases.

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.

<table><tbody><tr><td>1/4&quot;-20 nylon machine screws, knurled head thumb screw</td><td></td><td></td><td>to attach rod to PVC frame</td></tr><tr><td>1-1/4 inch PVC pipe</td><td></td><td></td><td>length of ~5-10 ft is needed</td></tr><tr><td>3T MRI scanner</td><td>Siemens</td><td></td><td></td></tr><tr><td>6-32 nylon machine screws, rounded head</td><td></td><td></td><td>to attach mirror/screen to rod</td></tr><tr><td>8-channel head array coil</td><td>Siemens</td><td></td><td></td></tr><tr><td>90 degree PVC elbow, 1-1/4 inch fitting</td><td></td><td></td><td></td></tr><tr><td>Acrylic mirror</td><td></td><td></td><td>Width and length of 25-30cm</td></tr><tr><td>Acrylic rod</td><td></td><td></td><td>1 inch width, ~ 2 ft long depening on size of scanner bore and head coil</td></tr><tr><td>E-Prime</td><td>Psychology Software Tools</td><td></td><td>to prepare and present visual stimuli paradigms</td></tr><tr><td>Plywood sheet, 1/2 inch thick</td><td></td><td></td><td>Size should be at least as large as the scanner bore. Cut as bore-sized frame for the projection screen</td></tr><tr><td>Rear projection screen</td><td></td><td></td><td>Size should be at least as large as the scanner bore</td></tr></tbody></table>

functional magnetic resonance imaging (fmri) of the visual cortex with wide-view retinotopic stimulation

High-resolution retinotopic blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) with a wide-view presentation can be used to functionally map the peripheral and central visual cortex. This method for measuring functional changes of the visual brain allows for functional mapping of the occipital lobe, stimulating &gt;100&#176; (&plusmn;50&#176;) or more of the visual field, compared to standard fMRI visual presentation setups which usually cover &lt;30&#176; of the visual field. A simple wide-view stimulation system for BOLD fMRI can be set up using common MR-compatible projectors by placing a large mirror or screen close to the subject's face and using only the posterior half of a standard head coil to provide a wide-viewing angle without obstructing their vision. The wide-view retinotopic fMRI map can then be imaged using various retinotopic stimulation paradigms, and the data can be analyzed to determine the functional activity of visual cortical regions corresponding to central and peripheral vision. This method provides a practical, easy-to-implement visual presentation system that can be used to evaluate changes in the peripheral and central visual cortex due to eye diseases such as glaucoma and the vision loss that may accompany them.

Nine participants diagnosed with POAG (four males, 36-74 years old) and nine age-matched healthy volunteers (six males, 53-65) were evaluated using the aforementioned wide-view fMRI protocol, as previously described by Zhou et al3. POAG was confirmed clinically in patients with an open angle by assessment of the presentation of visual field defects consistent with glaucoma, optic disc cupping, and/or an intraocular pressure (IOP) greater than 21 mmHg3. A wide-view visual presentation (&#177;55&#176;) was used to evaluate central and peripheral vision in each group3.
Figure 3 depicts the retinotopic fMRI maps for polar (wedge) and eccentricity (ring) stimuli from a POAG and healthy control participant. The polar maps (Figure 3A) revealed no obvious differences between the POAG and healthy participants. The eccentricity maps (Figure 3B) showed that the central region of the parafovea that was activated by the smaller ring stimuli appeared larger in the POAG patient compared to the healthy participant. The enlarged parafoveal region in the visual cortex of POAG participants suggests cortical changes in response to peripheral vision disturbances.
BOLD percent changes for central (&#60;24&#176;) and peripheral (&#62;24&#176;) visual fields between POAG subgroups and the healthy control group were compared (Figure 4). BOLD percent changes at different eccentricities were reduced in POAG patients compared to healthy control participants, primarily at more peripheral eccentricities (Figure 4A).&#160;The BOLD percent changes were significantly reduced between the two groups, more so at larger eccentricities&#160;(p &#60; 0.05, two-way ANOVA with Bonferroni post hoc test). The BOLD percent changes averaged for central vision (all stimuli &#60;24&#176;) were only slightly and not significantly reduced in POAG patients, while the BOLD response for peripheral vision (all stimuli &#62;24&#176;) was significantly reduced (Figure 4B).&#160;These results indicate this protocol&#39;s potential utility to assess changes in visual cortex function localized to peripheral or central vision, which is relevant to visual disorders such as glaucoma.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/65597/65597fig01.jpg" /> 
Figure 1: Experimental setup. (A) The 25 cm wide by 15 cm tall mirror held in place with a frame constructed from PVC pipe. (B) Setup of the presentation system on an MRI scanner, showing the posterior portion of a head array coil, the mirror and frame, and the back-projection screen (arrows) in the bore directly behind the head coil. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/65597/65597fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/65597/65597fig02.jpg" /> 
Figure 2: Visual stimulation paradigms. (A) Three frames from the polar retinotopic visual stimulation paradigm, which consist of clockwise and counterclockwise spinning wedges with a contrast-alternating checkerboard pattern. (B) Three frames from the eccentricity paradigm, which consist of expanding and contracting rings with a contrast-alternating checkerboard pattern. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/65597/65597fig02large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/65597/65597fig03v2.jpg" /> 
Figure 3: Retinotopic polar and eccentricity maps. Representative (A) polar map&#160;using a rotating wedge from a normal control and (B) eccentricity maps using expanding/contracting rings from a normal control and a POAG participant. Both the left and right hemispheres (LH and RH) are shown with defined visual cortical boundaries (V1, V2, and V3). One frame from each paradigm is shown in the central inset. The color scales map to the corresponding regions of the visual field, as indicated by the color wheels, with A) mapping to the polar angle of the wedge stimuli, and B) mapping to the eccentricity of the ring stimuli. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/65597/65597fig03largev2.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/65597/65597fig04.jpg" /> 
Figure 4: BOLD percent changes as a function of eccentricity and central or peripheral visual fields. (A) Group-averaged BOLD percent changes from the ring stimuli in healthy controls and POAG patients as a function of eccentricity. The BOLD percent change for each size of the ring stimuli were calculated to give the data at each eccentricity. (B) BOLD percent changes between healthy control and POAG patients of central (&#60; &#177;12&#176;) and peripheral (&#62; &#177;12&#176;) of the visual field, by binning data from all the eccentricities. Data are mean &#177; standard error of the mean. *p &#60; 0.05, two-factor ANOVA with post hoc correlation. This figure has been modified from Zhou et al.3 with permission. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/65597/65597fig04large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Insights into Visual Cortex Research Through Wide-View fMRI Mapping at JoVE.com

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

We have developed techniques for mapping the visual cortex function utilizing more of the visual field than is commonly used. This approach has the potential to enhance the evaluation of vision disorders and eye diseases.

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

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

functional-magnetic-resonance-imaging-fmri-visual-cortex-with-wide

Nanyang Technological University

Research

JoVE Journal

Neuroscience

1.4K Views.  Renaissance School of Medicine at Stony Brook University. Dit onderzoek richt zich op het bieden van een praktisch, kosteneffectief visueel presentatiesysteem om veranderingen in de visuele cortex als gevolg van oogheelkundige aandoeningen te evalueren. We bieden een methode om een atopische kaart met brede kijkhoek te maken, met behulp van FMRI om de functionele activiteit van de visuele cortex te beoordelen. Een huidige experimentele uitdaging is dat standaardsystemen voor het presenteren van visuele stimuli voor FMRI slechts een klein deel van de...

Video: Auteur in de schijnwerpers: inzichten in onderzoek naar visuele cortex door middel van breedbeeld fMRI-mapping 

Functional Magnetic Resonance Imaging (fMRI) with Auditory Stimulation in Songbirds

The neurobiology of birdsong, as a model for human speech, is a pronounced area of research in behavioral neuroscience. Whereas electrophysiology and molecular approaches allow the investigation of either different stimuli on few neurons, or one stimulus in large parts of the brain, blood oxygenation level dependent (BOLD) functional Magnetic Resonance Imaging (fMRI) allows combining both advantages, i.e. compare the neural activation induced by different stimuli in the entire brain at once. fMRI in songbirds is challenging because of the small size of their brains and because their bones and especially their skull comprise numerous air cavities, inducing important susceptibility artifacts. Gradient-echo (GE) BOLD fMRI has been successfully applied to songbirds 1-5 (for a review, see 6). These studies focused on the primary and secondary auditory brain areas, which are regions free of susceptibility artifacts. However, because processes of interest may occur beyond these regions, whole brain BOLD fMRI is required using an MRI sequence less susceptible to these artifacts. This can be achieved by using spin-echo (SE) BOLD fMRI 7,8 . In this article, we describe how to use this technique in zebra finches (Taeniopygia guttata), which are small songbirds with a bodyweight of 15-25 g extensively studied in behavioral neurosciences of birdsong. The main topic of fMRI studies on songbirds is song perception and song learning. The auditory nature of the stimuli combined with the weak BOLD sensitivity of SE (compared to GE) based fMRI sequences makes the implementation of this technique very challenging.

Functional Magnetic Resonance Imaging fMRI with Auditory Stimulation in Songbirds

This article shows an optimized procedure for imaging of the neural substrates of auditory stimulation in the songbird brain using functional Magnetic Resonance Imaging (fMRI). It describes the preparation of the sound stimuli, the positioning of the subject and the acquisition and subsequent analysis of the fMRI data.

The neurobiology of birdsong, as a model for human speech, is a pronounced area of research in behavioral neuroscience. Whereas electrophysiology and ...

Behavior

Topographical Estimation of Visual Population Receptive Fields by fMRI

Visual cortex is retinotopically organized so that neighboring populations of cells map to neighboring parts of the visual field. Functional magnetic resonance imaging allows us to estimate voxel-based population receptive fields (pRF), i.e., the part of the visual field that activates the cells within each voxel. Prior, direct, pRF estimation methods1 suffer from certain limitations: 1) the pRF model is chosen a-priori and may not fully capture the actual pRF shape, and 2) pRF centers are prone to mislocalization near the border of the stimulus space. Here a new topographical pRF estimation method2 is proposed that largely circumvents these limitations. A linear model is used to predict the Blood Oxygen Level-Dependent (BOLD) signal by convolving the linear response of the pRF to the visual stimulus with the canonical hemodynamic response function. PRF topography is represented as a weight vector whose components represent the strength of the aggregate response of voxel neurons to stimuli presented at different visual field locations. The resulting linear equations can be solved for the pRF weight vector using ridge regression3, yielding the pRF topography. A pRF model that is matched to the estimated topography can then be chosen post-hoc, thereby improving the estimates of pRF parameters such as pRF-center location, pRF orientation, size, etc. Having the pRF topography available also allows the visual verification of pRF parameter estimates allowing the extraction of various pRF properties without having to make a-priori assumptions about the pRF structure. This approach promises to be particularly useful for investigating the pRF organization of patients with disorders of the visual system.

It is important to obtain unbiased estimates of visual population receptive fields (pRFs) by functional magnetic resonance imaging. We use mild regularization constraints to estimate pRF topography without a-priori assumptions about pRF shape, allowing us to choose specific pRF models post-hoc. This is particularly advantageous in subjects with visual-pathway lesions.

Visual cortex is retinotopically organized so that neighboring populations of cells map to neighboring parts of the visual field. Functional magnetic ...

High-resolution Functional Magnetic Resonance Imaging Methods for Human Midbrain

Functional MRI (fMRI) is a widely used tool for non-invasively measuring correlates of human brain activity. However, its use has mostly been focused upon measuring activity on the surface of cerebral cortex rather than in subcortical regions such as midbrain and brainstem. Subcortical fMRI must overcome two challenges: spatial resolution and physiological noise. Here we describe an optimized set of techniques developed to perform high-resolution fMRI in human SC, a structure on the dorsal surface of the midbrain; the methods can also be used to image other brainstem and subcortical structures.
High-resolution (1.2 mm voxels) fMRI of the SC requires a non-conventional approach. The desired spatial sampling is obtained using a multi-shot (interleaved) spiral acquisition1. Since, T2* of SC tissue is longer than in cortex, a correspondingly longer echo time (TE ~ 40 msec) is used to maximize functional contrast. To cover the full extent of the SC, 8-10 slices are obtained. For each session a structural anatomy with the same slice prescription as the fMRI is also obtained, which is used to align the functional data to a high-resolution reference volume.
In a separate session, for each subject, we create a high-resolution (0.7 mm sampling) reference volume using a T1-weighted sequence that gives good tissue contrast. In the reference volume, the midbrain region is segmented using the ITK-SNAP software application2. This segmentation is used to create a 3D surface representation of the midbrain that is both smooth and accurate3. The surface vertices and normals are used to create a map of depth from the midbrain surface within the tissue4.
Functional data is transformed into the coordinate system of the segmented reference volume. Depth associations of the voxels enable the averaging of fMRI time series data within specified depth ranges to improve signal quality. Data is rendered on the 3D surface for visualization.
In our lab we use this technique for measuring topographic maps of visual stimulation and covert and overt visual attention within the SC1. As an example, we demonstrate the topographic representation of polar angle to visual stimulation in SC.

This article describes techniques to perform high-resolution functional magnetic resonance imaging with 1.2 mm sampling in human midbrain and subcortical structures using a 3T scanner. Use of these techniques to resolve topographic maps of visual stimulation in the human superior colliculus (SC) is given as an example.

Functional MRI (fMRI) is a widely used tool for non-invasively measuring correlates of human brain activity. However, its use has mostly been focused upon ...

Functional Neuroimaging Using Ultrasonic Blood-brain Barrier Disruption and Manganese-enhanced MRI

Although mice are the dominant model system for studying the genetic and molecular underpinnings of neuroscience, functional neuroimaging in mice remains technically challenging. One approach, Activation-Induced Manganese-enhanced MRI (AIM MRI), has been used successfully to map neuronal activity in rodents 1-5. In AIM MRI, Mn2+ acts a calcium analog and accumulates in depolarized neurons 6,7. Because Mn2+ shortens the T1 tissue property, regions of elevated neuronal activity will enhance in MRI. Furthermore, Mn2+ clears slowly from the activated regions; therefore, stimulation can be performed outside the magnet prior to imaging, enabling greater experimental flexibility. However, because Mn2+ does not readily cross the blood-brain barrier (BBB), the need to open the BBB has limited the use of AIM MRI, especially in mice.
One tool for opening the BBB is ultrasound. Though potentially damaging, if ultrasound is administered in combination with gas-filled microbubbles (i.e., ultrasound contrast agents), the acoustic pressure required for BBB opening is considerably lower. This combination of ultrasound and microbubbles can be used to reliably open the BBB without causing tissue damage 8-11.
Here, a method is presented for performing AIM MRI by using microbubbles and ultrasound to open the BBB. After an intravenous injection of perflutren microbubbles, an unfocused pulsed ultrasound beam is applied to the shaved mouse head for 3 minutes. For simplicity, we refer to this technique of BBB Opening with Microbubbles and UltraSound as BOMUS 12. Using BOMUS to open the BBB throughout both cerebral hemispheres, manganese is administered to the whole mouse brain. After experimental stimulation of the lightly sedated mice, AIM MRI is used to map the neuronal response.
To demonstrate this approach, herein BOMUS and AIM MRI are used to map unilateral mechanical stimulation of the vibrissae in lightly sedated mice 13. Because BOMUS can open the BBB throughout both hemispheres, the unstimulated side of the brain is used to control for nonspecific background stimulation. The resultant 3D activation map agrees well with published representations of the vibrissae regions of the barrel field cortex 14. The ultrasonic opening of the BBB is fast, noninvasive, and reversible; and thus this approach is suitable for high-throughput and/or longitudinal studies in awake mice.

A technique is described for broadly opening the blood-brain barrier in the mouse using microbubbles and ultrasound. Using this technique, manganese can be administered to the mouse brain. Because manganese is an MRI contrast agent that accumulates in depolarized neurons, this approach enables imaging of neuronal activity.

Although mice are the dominant model system for studying the genetic and molecular underpinnings of neuroscience, functional neuroimaging in mice remains ...

Functional Imaging of Auditory Cortex in Adult Cats using High-field fMRI

Current knowledge of sensory processing in the mammalian auditory system is mainly derived from electrophysiological studies in a variety of animal models, including monkeys, ferrets, bats, rodents, and cats. In order to draw suitable parallels between human and animal models of auditory function, it is important to establish a bridge between human functional imaging studies and animal electrophysiological studies. Functional magnetic resonance imaging (fMRI) is an established, minimally invasive method of measuring broad patterns of hemodynamic activity across different regions of the cerebral cortex. This technique is widely used to probe sensory function in the human brain, is a useful tool in linking studies of auditory processing in both humans and animals and has been successfully used to investigate auditory function in monkeys and rodents. The following protocol describes an experimental procedure for investigating auditory function in anesthetized adult cats by measuring stimulus-evoked hemodynamic changes in auditory cortex using fMRI. This method facilitates comparison of the hemodynamic responses across different models of auditory function thus leading to a better understanding of species-independent features of the mammalian auditory cortex.

Functional studies of the auditory system in mammals have traditionally been conducted using spatially-focused techniques such as electrophysiological recordings. The following protocol describes a method of visualizing large-scale patterns of evoked hemodynamic activity in the cat auditory cortex using functional magnetic resonance imaging.

Current knowledge of sensory processing in the mammalian auditory system is mainly derived from electrophysiological studies in a variety of animal ...

Extracting Visual Evoked Potentials from EEG Data Recorded During fMRI-guided Transcranial Magnetic Stimulation

Transcranial Magnetic Stimulation (TMS) is an effective method for establishing a causal link between a cortical area and cognitive/neurophysiological effects. Specifically, by creating a transient interference with the normal activity of a target region and measuring changes in an electrophysiological signal, we can establish a causal link between the stimulated brain area or network and the electrophysiological signal that we record. If target brain areas are functionally defined with prior fMRI scan, TMS could be used to link the fMRI activations with evoked potentials recorded. However, conducting such experiments presents significant technical challenges given the high amplitude artifacts introduced into the EEG signal by the magnetic pulse, and the difficulty to successfully target areas that were functionally defined by fMRI. Here we describe a methodology for combining these three common tools: TMS, EEG, and fMRI. We explain how to guide the stimulator&#39;s coil to the desired target area using anatomical or functional MRI data, how to record EEG during concurrent TMS, how to design an ERP study suitable for EEG-TMS combination and how to extract reliable ERP from the recorded data. We will provide representative results from a previously published study, in which fMRI-guided TMS was used concurrently with EEG to show that the face-selective N1 and the body-selective N1 component of the ERP are associated with distinct neural networks in extrastriate cortex. This method allows us to combine the high spatial resolution of fMRI with the high temporal resolution of TMS and EEG and therefore obtain a comprehensive understanding of the neural basis of various cognitive processes.

This paper describes a method for collecting and analyzing electroencephalography (EEG) data during concurrent transcranial magnetic stimulation (TMS) guided by activations revealed with functional magnetic resonance imaging (fMRI). A method for TMS artifact removal and extraction of event related potentials is described as well as considerations in paradigm design and experimental setup.

Transcranial Magnetic Stimulation (TMS) is an effective method for establishing a causal link between a cortical area and cognitive/neurophysiological ...

The Use of Magnetic Resonance Spectroscopy as a Tool for the Measurement of Bi-hemispheric Transcranial Electric Stimulation Effects on Primary Motor Cortex Metabolism

Transcranial direct current stimulation (tDCS) is a neuromodulation technique that has been increasingly used over the past decade in the treatment of neurological and psychiatric disorders such as stroke and depression. Yet, the mechanisms underlying its ability to modulate brain excitability to improve clinical symptoms remains poorly understood 33. To help improve this understanding, proton magnetic resonance spectroscopy (1H-MRS) can be used as it allows the in vivo quantification of brain metabolites such as &#947;-aminobutyric acid (GABA) and glutamate in a region-specific manner 41. In fact, a recent study demonstrated that 1H-MRS is indeed a powerful means to better understand the effects of tDCS on neurotransmitter concentration 34. This article aims to describe the complete protocol for combining tDCS (NeuroConn MR compatible stimulator) with 1H-MRS at 3 T using a MEGA-PRESS sequence. We will describe the impact of a protocol that has shown great promise for the treatment of motor dysfunctions after stroke, which consists of bilateral stimulation of primary motor cortices 27,30,31. Methodological factors to consider and possible modifications to the protocol are also discussed.

This article aims to describe a basic protocol for combining transcranial direct current stimulation (tDCS) with proton magnetic resonance spectroscopy (1H-MRS) measurements to investigate the effects of bilateral stimulation on primary motor cortex metabolism.

Transcranial direct current stimulation (tDCS) is a neuromodulation technique that has been increasingly used over the past decade in the treatment of ...

A Large Lateral Craniotomy Procedure for Mesoscale Wide-field Optical Imaging of Brain Activity

The craniotomy is a commonly performed procedure to expose the brain for in vivo experiments. In mouse research, most labs utilize a small craniotomy, typically 3 mm x 3 mm. This protocol introduces a method for creating a substantially larger 7 mm x 6 mm cranial window exposing most of a cerebral hemisphere over the mouse temporal and parietal cortices (e.g., bregma 2.5 - 4.5 mm, lateral 0 - 6 mm). To perform this surgery, the head must be tilted approximately 30&#176; and much of the temporal muscle must be retracted. Due to the large amount of bone removal, this procedure is intended only for acute experiments with the animal anesthetized throughout the surgery and experiment.
The main advantage of this innovative large lateral cranial window is to provide simultaneous access to both medial and lateral areas of the cortex. This large unilateral cranial window can be used to study the neural dynamics between cells, as well as between different cortical areas by combining multi-electrode electrophysiological recordings, imaging of neuronal activity (e.g., intrinsic or extrinsic imaging), and optogenetic stimulation. Additionally, this large craniotomy also exposes a large area of cortical blood vessels, allowing for direct manipulation of the lateral cortical vasculature.

This protocol presents a method for creating a large unilateral craniotomy over the temporal and parietal regions of the mouse cerebral cortex. This is especially useful for real time imaging over an expansive area of a cortical hemisphere.

The craniotomy is a commonly performed procedure to expose the brain for in vivo experiments. In mouse research, most labs utilize a small craniotomy, ...

Optogenetic Functional MRI

The investigation of the functional connectivity of precise neural circuits across the entire intact brain can be achieved through optogenetic functional magnetic resonance imaging (ofMRI), which is a novel technique that combines the relatively high spatial resolution of high-field fMRI with the precision of optogenetic stimulation. Fiber optics that enable delivery of specific wavelengths of light deep into the brain in vivo are implanted into regions of interest in order to specifically stimulate targeted cell types that have been genetically induced to express light-sensitive trans-membrane conductance channels, called opsins. fMRI is used to provide a non-invasive method of determining the brain's global dynamic response to optogenetic stimulation of specific neural circuits through measurement of the blood-oxygen-level-dependent (BOLD) signal, which provides an indirect measurement of neuronal activity. This protocol describes the construction of fiber optic implants, the implantation surgeries, the imaging with photostimulation and the data analysis required to successfully perform ofMRI. In summary, the precise stimulation and whole-brain monitoring ability of ofMRI are crucial factors in making ofMRI a powerful tool for the study of the connectomics of the brain in both healthy and diseased states.

This protocol describes the steps and data analysis required to successfully perform optogenetic functional magnetic resonance imaging (ofMRI). ofMRI is a novel technique that combines high-field fMRI readout with optogenetic stimulation, allowing for cell type-specific mapping of functional neural circuits and their dynamics across the whole living brain.

The investigation of the functional connectivity of precise neural circuits across the entire intact brain can be achieved through optogenetic functional ...

Stimulus-specific Cortical Visual Evoked Potential Morphological Patterns

This paper presents a methodology for the recording and analysis of cortical visual evoked potentials (CVEPs) in response to various visual stimuli using 128-channel high-density electroencephalography (EEG). The specific aim of the described stimuli and analyses is to examine whether it is feasible to replicate previously reported CVEP morphological patterns elicited by an apparent motion stimulus, designed to simultaneously stimulate both ventral and dorsal central visual networks, using object and motion stimuli designed to separately stimulate ventral and dorsal visual cortical networks.&#160; Four visual paradigms are presented: 1. Randomized visual objects with consistent temporal presentation. 2. Randomized visual objects with inconsistent temporal presentation (or jitter).&#160; 3. Visual motion via a radial field of coherent central dot motion without jitter.&#160; 4. Visual motion via a radial field of coherent central dot motion with jitter.&#160; These four paradigms are presented in a pseudo-randomized order for each participant.&#160; Jitter is introduced in order to view how possible anticipatory-related effects may affect the morphology of the object-onset and motion-onset CVEP response.&#160; EEG data analyses are described in detail, including steps of data exportation from and importation to signal processing platforms, bad channel identification&#160;and removal, artifact rejection, averaging, and categorization of average CVEP morphological pattern type based upon latency ranges of component peaks. Representative data show that the methodological approach is indeed sensitive in eliciting differential object-onset and motion-onset CVEP morphological patterns and may, therefore, be useful in addressing the larger research aim. Given the high temporal resolution of EEG and the possible application of high-density EEG in source localization analyses, this protocol is ideal for the investigation of distinct CVEP morphological patterns and the underlying neural mechanisms which generate these differential responses.&#160; &#160; &#160;&#160;

In this paper, we present a protocol to investigate differential cortical visual evoked potential morphological patterns through stimulation of ventral and dorsal networks using high-density EEG. Visual object and motion stimulus paradigms, with and without temporal jitter, are described. Visual evoked potential morphological analyses are also outlined.&#160;&#160;

This paper presents a methodology for the recording and analysis of cortical visual evoked potentials (CVEPs) in response to various visual stimuli using ...

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

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