Functional magnetic resonance imaging of the visual system.
ABSTRACT Functional magnetic resonance imaging (fMRI), which is a technique useful for non-invasive mapping of brain function, is well suited for studying the visual system. This review highlights current clinical applications and research studies involving patients with visual deficits. Relevant reports regarding the investigation of the brain's role in visual processing and some newer fMRI techniques are also reviewed. Functional magnetic resonance imaging has been used for presurgical mapping of visual cortex in patients with brain lesions and for studying patients with amblyopia, optic neuritis, and residual vision in homonymous hemianopia. Retinotopic borders, motion processing, and visual attention have been the topics of several fMRI studies. These reports suggest that fMRI can be useful in clinical and research studies in patients with visual deficits.
- SourceAvailable from: Ram Lakhan Pandey Vimal
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- "Although there is a wealth of literature on vision and brain imaging (Paradiso, 2000; Miki et al., 2001), most studies involve lower level processing andyor full visual fields, and so are not directly "
ABSTRACT: We examined whether lateral visual field stimulation (LSTM) could activate contralateral extrastriate cortical areas as predicted by a large experimental literature. We asked seven unscreened, control subjects to wear glasses designed to allow vision out of either the left (LVF) or right lateral visual field (RVF) depending upon which side the subject looked toward. Each subject participated in a block design functional magnetic resonance imaging (fMRI) study with alternating 30-s epochs in which he was asked to look to one side and then the other for a total of five epochs. On each side of the bore of the scanner, we taped a photograph for the subject to view in the LVF and RVF. The data were analyzed with SPM99 using a fixed effect, box-car design with contrasts for the LVF and the RVF conditions. Both LVF and RVF conditions produced the strongest fMRI activation in the contralateral occipitotemporal and posterior parietal areas as well as the contralateral dorsolateral prefrontal cortex. LSTM appears to increase contralateral fMRI activation in striate and extrastriate cortical areas as predicted by earlier studies reporting differential cognitive and/or emotional effects from unilateral sensory or motor stimulation.Psychiatry Research 06/2004; 131(1):1-9. DOI:10.1016/j.pscychresns.2004.01.002 · 2.68 Impact Factor
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ABSTRACT: Functional magnetic resonance imaging (fMRI) is a powerful, non-invasive technique for mapping human brain function. Because of the robust signal intensity changes associated with visual stimuli, fMRI is particularly useful for studying visual cortex (including both striate and extrastriate cortex). Also, activation of the lateral geniculate nuclei has been successfully demonstrated by fMRI. Therefore, fMRI may be potentially useful in patients with visual deficits by providing a non-invasive method for assessing the afferent visual pathways and higher cortical areas. Although there have been several reviews on fMRI, few have highlighted its clinical applicability in patients with visual disturbances. Our article will review fMRI principles and methodology, then focus on the possible applications and limitations of this technique in clinical ophthalmology.Survey of Ophthalmology 11/2002; 47(6):562-79. DOI:10.1016/S0039-6257(02)00356-9 · 3.51 Impact Factor
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ABSTRACT: The aim of this article is to review the controversial findings for NovaVision's vision restoration therapy. It has been claimed that NovaVision's computerized therapy results in expansion of the visual field in optic nerve and occipital lesions, but the outcome has been challenged on the grounds of unsatisfactory perimetric control of central fixation and disputed mechanisms. In clinical practice NovaVision's therapy should not currently gain acceptance in view of unacceptable perimetric standards and equivocal results. Possible effects on a relative scotoma at the edge of a lesion have not been adequately explored. In the interim, research should also be focused on compensatory eye movement strategies.Current Opinion in Ophthalmology 01/2007; 17(6):498-503. DOI:10.1097/ICU.0b013e3280108544 · 2.64 Impact Factor