---------- Forwarded message ----------
Date: 11 Apr 96 16:25:25 EDT
From: Jamal Mazrui <74444.1076@CompuServe.COM>
To: BlindCopyReceiver: ;
Subject: Post article on braille
I came across this article about braille reading in today's Washington Post.
Thought it would interest you.
Jamal
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04/11/96 -- (C) 1996 The Washington Post (LEGI-SLATE Article No. 252205)
Braille Readers Found to Use Visual Cortex
Results Defy Traditional Ideas of Brain Function
By Curt Suplee
Washington Post Staff Writer
When blind people "read" Braille with their fingertips, they are somehow
able to use the same part of the brain -- called the visual cortex -- that
sighted persons use to interpret things they see.
That's the conclusion of new experiments that challenge traditional
ideas about how sensory information is processed in the brain.
According to orthodox neuroscience, tactile stimuli are processed in a
region of the brain's convoluted outer layer called the somatosensory cortex.
Visual information goes by a completely different route to an area at the
back of the brain called the visual cortex. Eventually, the twain may meet
and be integrated into a single perception -- but only after each has been
separately processed. There are no known nerve pathways that would permit
tactile signals to get to the visual cortex directly.
But in today's issue of the journal Nature, researchers from the
National Institute of Neurological Disorders and Stroke here report that
persons who are blind from an early age seem to have rearranged their neural
wiring so that sensory information from a forefinger running over patterns of
raised Braille dots prompts a flurry of action in the brain's visual
processing centers.
Norihiro Sadato and colleagues at NINDS monitored the cerebral activity
of eight adept Braille readers, six other blind subjects and 10 sighted
subjects using a technique called positron emission tomography. PET scans
show which areas of the brain are most active (that is, which cells are
consuming the most blood-borne nutrients) during a given task.
In this case, the eight blind subjects were scanned while they read
raised dot patterns in Braille. The other subjects were monitored while
performing various analogous tasks: running their fingers over a uniform grid
of Braille dots; feeling the size and angle of grooves in an array of dots;
and detecting dot patterns of English letters.
When sighted subjects performed those tasks, their scans showed
diminished activity in the visual cortex and the expected levels of action in
somatosensory areas that normally process touch information. But when any of
the 14 blind subjects read Braille or interpreted dot patterns, they
exhibited substantial increases in the visual cortex. Neither group showed
any visual cortex activity during the "non-discriminatory" task of merely
sweeping their fingers over the uniform dot grid, which involved purely
tactile sensation.
Recent research has shown that when people create imaginary mental
images of objects, brain activity increases in the same parts of the visual
cortex that are used when actually viewing an object. But none of the NINDS
subjects was asked to form mental pictures during any of the tasks, and none
reported doing so. Moreover, some of the subjects were blind from birth and
presumably had no way to form imagined visual images.
So how did the Braille readers use the visual cortex, and what mechanism
might make that possible? "That's the million-dollar question," said NINDS
neuropsychologist Jordan Grafman, a co-author of the Nature paper. "One
hypothesis is that there are certain properties of cells in the visual cortex
that resemble properties of cells in the somatosensory cortex" -- especially
in their ability to discriminate geometrical information about a stimulus.
"If that's true," he said, "then it might be possible under special
conditions that cells in either . . . cortex could adapt to sensory input
coming from the other area."
It is conceivable, the NINDS team suspects, that information can travel
from region to region through some unknown "indirect preexisting pathway." In
normal circumstances, in which a sighted person is touching something, that
pathway would be shut down to focus attention on tactile stimuli and avoid
confusing the brain.
But that pathway might be opened "in an emergency or unusual situation"
such as blindness, Grafman said.
Once the phenomenon is better understood, he said, it might be possible
to concoct drugs that would encourage this kind of compensatory re-routing,
known as neural plasticity.
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