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J Neurophysiol (December 1, 2002). 10.1152/jn.00129.2002
Submitted on 21 February 2002
Accepted on 6 August 2002
1Department of Anatomy and Neurobiology, 2Department of Neurology and Neurological Surgery, and 3Department of Radiology, Washington University School of Medicine, St. Louis, Missouri 63110
Burton, H.,
A. Z. Snyder,
J. B. Diamond, and
M. E. Raichle.
Adaptive Changes in Early and Late Blind: A fMRI Study of Verb
Generation to Heard Nouns. J. Neurophysiol. 88: 3359-3371, 2002. Literacy for blind people requires
learning Braille. Along with others, we have shown that reading Braille
activates visual cortex. This includes striate cortex (V1), i.e., banks
of calcarine sulcus, and several higher visual areas in lingual,
fusiform, cuneus, lateral occipital, inferior temporal, and middle
temporal gyri. The spatial extent and magnitude of magnetic resonance
(MR) signals in visual cortex is greatest for those who became blind early in life. Individuals who lost sight as adults, and subsequently learned Braille, still exhibited activity in some of the same visual
cortex regions, especially V1. These findings suggest these visual
cortex regions become adapted to processing tactile information and
that this cross-modal neural change might support Braille literacy.
Here we tested the alternative hypothesis that these regions directly
respond to linguistic aspects of a task. Accordingly, language task
performance by blind persons should activate the same visual cortex
regions regardless of input modality. Specifically, visual cortex
activity in blind people ought to arise during a language task
involving heard words. Eight early blind, six late blind, and eight
sighted subjects were studied using functional magnetic resonance
imaging (fMRI) during covert generation of verbs to heard nouns. The
control task was passive listening to indecipherable sounds (reverse
words) matched to the nouns in sound intensity, duration, and spectral
content. Functional responses were analyzed at the level of individual
subjects using methods based on the general linear model and at the
group level, using voxel based ANOVA and t-test analyses.
Blind and sighted subjects showed comparable activation of language
areas in left inferior frontal, dorsolateral prefrontal, and left
posterior superior temporal gyri. The main distinction was bilateral,
left dominant activation of the same visual cortex regions previously
noted with Braille reading in all blind subjects. The spatial extent and magnitude of responses was greatest on the left in early blind individuals. Responses in the late blind group mostly were confined to
V1 and nearby portions of the lingual and fusiform gyri. These results
confirm the presence of adaptations in visual cortex of blind people
but argue against the notion that this activity during Braille reading
represents somatosensory (haptic) processing. Rather, we suggest that
these responses can be most parsimoniously explained in terms of
linguistic operations. It remains possible that these responses
represent adaptations which initially are for processing either sound
or touch, but which are later generalized to the other modality during
acquisition of Braille reading skills.
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