FMRI of human visual pathways

DOI: 10.1007/978-1-4419-0345-7_26 In book: Functional Neuroradiology, pp.485-511


Functional magnetic resonance imaging (fMRI) of the human brain provides images of changes in local blood flow and oxygenation
that are evoked by sensory, motor, or cognitive events. Functional MRI has been used since 1991 [1] to identify areas of the
brain that respond to visual stimulation and the performance of vision-related tasks. Increasingly, fMRI is accompanied by
diffusion tensor imaging (DTI), which provides images of the speed and direction of diffusion of water molecules in the brain.
Fortuitously, this allows remarkable differentiation of cerebral white mater and the delineation of a variety of major white
matter tracts including vision-related pathways such as the optic radiations. This chapter focuses primarily on fMRI, but
DTI data are also discussed where relevant. Together, the two methods provide a wealth of information about the anatomical
and functional status of key components of the visual system in individual patients even in the presence of pathology. For
example, an imaging-based map of the visual system can be helpful for planning and guiding surgical resection of tumors impacting
critical vision-related brain structures. This is especially true when mass effects or previous surgeries have distorted the
normal anatomy making it difficult to know where key structures are located and if they are still functional. In difficult
cases, identifying the region of “closest approach” of a planned resection to the cortical representation of central vision
or to the optic radiations can help to minimize the risk to eloquent neural tissue and thereby avoid significant treatment-induced
vision loss while still permitting maximum therapeutic effect.

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    • "The ability to identify the representation of central vision makes temporal phase mapping particularly useful for pre-surgical planning and generally superior to simple flashed checkerboards or pulsed lights (DeYoe et al., 2011). It is also time efficient in that all eccentricities or polar angles throughout the visual field can be mapped in less than 4 min. "
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    ABSTRACT: fMRI is becoming an important clinical tool for planning and guidance of surgery to treat brain tumors, arteriovenous malformations, and epileptic foci. For visual cortex mapping, the most popular paradigm by far is temporal phase mapping, although random multifocal stimulation paradigms have drawn increased attention due to their ability to identify complex response fields and their random properties. In this study we directly compared temporal phase and multifocal vision mapping paradigms with respect to clinically relevant factors including: time efficiency, mapping completeness, and the effects of noise. Randomized, multifocal mapping accurately decomposed the response of single voxels to multiple stimulus locations and made correct retinotopic assignments as noise levels increased despite decreasing sensitivity. Also, multifocal mapping became less efficient as the number of stimulus segments (locations) increased from 13 to 25 to 49 and when duty cycle was increased from 25% to 50%. Phase mapping, on the other hand, activated more extrastriate visual areas, was more time efficient in achieving statistically significant responses, and had better sensitivity as noise increased, though with an increase in systematic retinotopic mis-assignments. Overall, temporal phase mapping is likely to be a better choice for routine clinical applications though random multifocal mapping may offer some unique advantages for selected applications.
    Clinical neuroimaging 08/2013; 3:143-54. DOI:10.1016/j.nicl.2013.08.004 · 2.53 Impact Factor
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    ABSTRACT: It remains unclear to what extent retinotopic maps can undergo large-scale plasticity following damage to human visual cortex. The literature has predominately focused on retinotopic changes in patients with retinal pathologies or congenital brain malformations. Yet, damage to the adult visual cortex itself is common in cases such as stroke, tumor, or trauma. To address this issue, we used a unique database of fMRI vision maps in patients with adult-onset (n = 25) and congenital (n = 2) pathology of the visual cortex. We identified atypical retinotopic organization in three patients (two with adult-onset, and one with congenital pathology) consisting of an expanded ipsilateral field representation that was on average 3.2 times greater than healthy controls. The expanded representations were located at the vertical meridian borders between visual areas such as V1/V2. Additionally, two of the three patients had apparently an ectopic (topographically inconsistent) representation of the ipsilateral field within lateral occipital cortex that is normally associated with visual areas V3/V3A (and possibly other areas). Both adult-onset cases had direct damage to early visual cortex itself (rather than to the afferent drive only), resulting in a mostly nonfunctional hemisphere. The congenital case had severe cortical malformation of the visual cortex and was acallosal. Our results are consistent with a competitive model in which unilateral damage to visual cortex or disruption of the transcallosal connections removes interhemispheric suppression from retino-geniculate afferents in intact visual cortex that represent the vertical meridian and ipsilateral visual field.
    The Journal of Neuroscience : The Official Journal of the Society for Neuroscience 08/2013; 33(32):13010-24. DOI:10.1523/JNEUROSCI.0240-13.2013 · 6.34 Impact Factor
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    ABSTRACT: Functional magnetic resonance imaging (fMRI) is used clinically to map the visual cortex before brain surgery or other invasive treatments to achieve an optimal balance between therapeutic effect and the avoidance of postoperative vision deficits. Clinically optimized stimuli, behavioral task, analysis, and displays permit identification of cortical subregions supporting high-acuity central vision that is critical for reading and other essential visual functions. Emerging techniques such as resting-state fMRI may facilitate the use of fMRI-based vision mapping in a broader range of patients. Copyright © 2014 Elsevier Inc. All rights reserved.
    Neuroimaging Clinics of North America 11/2014; 24(4). DOI:10.1016/j.nic.2014.08.001 · 1.53 Impact Factor
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