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J.P. Szlyk, D.M. Little, D. Modi, K.R. Thulborn; Brain Networks Implicated in Word Identification in Patients With AMD Shown by fMRI . Invest. Ophthalmol. Vis. Sci. 2006;47(13):5875.
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To evaluate the cortical networks involved in word recognition using functional magnetic resonance imaging (fMRI) in patients with impaired reading due to age–related macular degeneration (AMD).
We recruited 5 patients (age range 55 to 83 years) who were enrolled in a reading rehabilitation program. The patients’ visual acuities in their better seeing eyes ranged from 20/76 to 20/360. The networks involved in word recognition were evaluated across two separate paradigms presented while fMRI data were acquired. The paradigms were identical with the exception of the length of target words (3 or 6 letters). Both were blocked paradigms with a 30sec block of word identification alternated with 30sec of rest. Each letter within each word subtended 2 deg, equivalent to about a 20/600 letter size. Each word was presented in the center of the monitor. A response was required indicating whether the target word represented something that is living or nonliving. Eye movements were monitored during fMRI sessions. Data were collected on a 3.0–Tesla scanner using serial gradient echo, echo–planar imaging. Data were analyzed with SPM2 and individual statistics were calculated to identify areas of greater activation during word recognition compared to rest. Additional data were collected from normally sighted control subjects.
The networks involved in word recognition for AMD patients were identified to include the frontal eye fields; both superior and inferior parietal lobules; the superior temporal gyri; middle temporal gyrus; fusiform gyri, bilateral hippocampus and the visual cortex. Although these networks were similar, the volumes of activation across these regions were more reduced for 6 letter compared to 3 letter words.
We interpret decreased activation in the 6 letter versus the 3 letter task as indicative of an increased reliance on top–down processing, and decreased reliance on bottom–up letter identification.
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