Fw: Brain Wiring for Human Language

[Jean Boutcher]

>From the newsroom of the Scientific American, Wednesday, October 3, 2001
......

NEUROSCIENCE

Brain Wiring for Human Language

Scientists have long been interested how the deaf process signed
languages
in the brain. Understanding that activity could shed light on whether the
brain harbors specialized structures for decoding linguistic patterns in
general - regardless of how they are conveyed. In fact, a new study
published in Tuesday's issue of the Proceedings of the National Academy
of
Science ( http://www.pnas.org/) suggests that the brain does have such
wiring, challenging the idea that speech and sound are vital for human
language. Laura Ann Petitto
(http://www.psych.mcgill.ca/faculty/petitto/petitto.html) and Robert
Zatorre
(http://www.bic.mni.mcgill.ca/~zlab/) of McGill University and their
colleagues base their conclusions on a series of experiments
(http://www.psych.mcgill.ca/faculty/petitto/PNASmovies.html) using
positron
emission tomography (PET) brain scans of 11 profoundly deaf people and 10
hearing people.

Earlier work had demonstrated that deaf people processing signed
sentences
used mostly their left hemispheres, just as hearing people parsing spoken
language did. But the new study found that in addition, both groups rely
on
identical brain structures for similar tasks. Petitto and Zatorre's team
discovered that deaf people searching for and retrieving signs showed
greater activity in the left inferior frontal cortex-the same region that
lights up in PET scans when hearing people rack their brains for words.
And
when the deaf subjects in the study processed meaningless grammatical
hand
movements, they showed greater blood flow in the planum temporale. In
hearing individuals, this brain region handles the spoken
equivalent-incoming meaningless syllables (such as ba, ta, da and pa)
from
which all words are made.

The researchers were particularly stunned by this activity in the planum
temporale among the deaf. For more than 100 years, scientists have
thought
that the tissues there-which receive neural projections from the
ears-exclusively processed sounds, and nothing else. The puzzling finding
has led Petitto and Zatorre to propose that perhaps areas of the brain
once
viewed as devoted to sounds actually contain different types of cells
capable of responding to the patterns of natural language in any form.
"Such
neural specialization for aspects of language patterning appears to be
neurally unmodifiable in so far as languages with radically different
sensory modalities such as speech and sign are processed at similar brain
sites," the authors write, "while, at the same time, the neural pathways
for
expressing and perceiving natural language appear to be neurally highly
modifiable."

-Kristin Leutwyler.

 z  1996-2001 Scientific American, Inc.

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