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Mindís eye in the deaf
7 January 2002
by Yang Jiang email@example.com
Finney E. M et al. (2001). Visual stimuli activate auditory cortex in
the deaf. Nat Neurosci, 4:1171-1173.
Typically, we see with our eyes, and visual information such as a view
of our surroundings is sent to the visual cortex in the brain for
further processing. We hear through our ears, and auditory information
such as music is projected to the auditory cortex. However, owing to the
lack of visual input, the visual cortices of blind people do not develop
normally. Previous studies have revealed that the visual cortex in blind
peopleís brains can be activated by auditory or tactile stimulation. A
new study reports a parallel finding Ė visual activation in the auditory
cortex of early deaf people.
Using functional brain imaging (fMRI), Finney et al. compared visually
evoked cortical activation in six profoundly deaf and six healthy
hearing people. When watching moving dot patterns, the deaf peopleís
right auditory cortices (Brodmann area 41, 42 and 22) showed
significantly more responses to the visual stimuli, compared with the
hearing subjects. As we know, the primary and secondary auditory
cortices have anatomical connections to secondary visual areas. These
results demonstrate the possibility that part of the visual information
is routed to the auditory areas of the brain in deaf people.
In a second experiment, both groups of subjects were told to ignore the
moving patterns by focusing their attention to the center fixation. The
hearing and deaf peopleís cortices responded differently for this
attention task as well. Even when visual motion was ignored, visual
activation in the auditory cortex in the deaf was observed. It has been
reported that auditory cortices of the deaf people could be activated by
visual images of sign languages. The current study provides evidence
that the auditory areas respond to non-language visual stimuli as well.
This demonstration of cross-modal plasticity in the auditory cortex of
the deaf echoes the complementary findings in the visual cortex of the
blind and the evidence points to the brainís capability to create the
mindís eye (or ear) in the underdeveloped cortex of the deaf (or blind).
Of course, further investigations on humans and animals are necessary
before we can fully understand how the deprived cortex is used to
process re-routed sensory information from a different cortical area.
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