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D.A. Poggel, J.F. Rizzo, III, L.J. Toth, D.–S. Kim; Retinotopy and fMRI–Based Visual Field Testing in Healthy Subjects . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3693.
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© ARVO (1962-2015); The Authors (2016-present)
Retinotopic mapping is an established method to determine the functional anatomy of early visual brain areas. However, its spatial resolution is low compared to behavioral visual field mapping. Ideally, an fMRI–based visual field test would permit objective and more spatially detailed mapping of visual field defects.
In 10 normally–sighted subjects, retinotopic mapping and fMRI–based visual field testing was performed in one experimental session using a 3T Philips Intera MR Scanner (FEEPI, TR=2000ms, 28 slices, 2mm, no gap, resolution 128 x 128). Retinotopic mapping stimulation consisted of a clockwise rotating wedge and an expanding annulus (5 cycles, 32s per cycle, 8Hz flicker, black–and white checkerboard). For the fMRI–based visual field test, small flickering stimuli (∼2.5 to 12.5 degrees eccentricity, M–scaled) were presented at 48 positions, with two randomly positioned stimuli appearing in each trial (2000ms), one in the left and one in the right hemifield. BOLD response, stimulus detection, and reaction times were acquired in five runs with a total of 30 repetitions at each position (5.5 min/ run). Data were analyzed with Brain Voyager software (GLM, event–related analysis, linear correlation maps) separately for the left and right hemisphere. Statistical activation maps for retinotopy and fMRI–based visual field test runs were superimposed to check for the consistency and validity of the results.
Retinotopic mapping yielded strong activation of the early visual cortical areas and was comparable to results reported in the literature. Eccentricity and polar angle mapping served as a reference for localizing activation for the 48 visual field locations of the fMRI–based visual field test. This activation was locally specific and was found at the locations expected based on retinotopy results.
Our new fMRI–based visual field test is a time–efficient and objective tool for testing visual field function with a higher spatial resolution than conventional retinotopic mapping. It permits point–by–point relation of behavioral parameters (stimulus detection, reaction times) to locally specific activation of early visual cortical areas. Thus, our method is also suitable for the assessment of visual field functionality visually impaired patients.
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