This is, I think, an interesting article about hands
and language.
Nature Reviews Neuroscience 2, 76 (2001)
LANGUAGE
The hands that hold the keys
Peter Collins
We have known for more than a century that the left
hemisphere is the primary site for language
processing in the brain because lesions of the left
hemisphere have often resulted in disorders of speech
and language.
But it is less clear why the left hemisphere is
dominant for language. Is it because the left side of
the brain is dedicated to processing the motor aspects
of speaking and the sensory aspects of hearing or is
it because the left side of the brain is specifically
involved in processing the linguistic patterns of
language? Clearly, it will be extremely difficult to
answer this question by studying speech-based
languages alone. One alternative is to study languages
that are not speech-based but still possess linguistic
structure — so dissociating the processing of speech
from the processing of the structure of language.
Languages that are not speech-based include the
naturally evolved sign languages of deaf people such
as American Sign Language. These languages possess
phonological,
morphological and syntactic levels of language
organization homologous to those in spoken languages,
convey the full semantic and grammatical expressive
range, and use similar conversational rules to spoken
languages.
A recent study by Laura
Petitto, Robert Zatorre
and colleagues at McGill
University built on
previous work with
naturally evolved sign
languages and their use
by profoundly deaf
subjects to probe the
neural basis of language
organization using
positron emission
tomography. Cerebral
blood flow activity was
observed in profoundly
deaf subjects processing
specific aspects of sign
language in areas of the
brain that are widely
assumed to be unimodal
for speech or sound.
Specifically, activity was
observed in the left
inferior frontal cortex
when deaf signers
produced meaningful
signed verbs in response
to a signed noun. These
results suggest that
specific sites of the left
frontal cortex are
recruited for higher-order
linguistic processes
related to lexical
operations that do not depend on the presence of
sound. In addition, activity was observed bilaterally
in an area of the superior temporal gyrus (STG) — the
planum temporale (PT) — when deaf subjects viewed
signs or meaningless parts of signs (equivalent to
phonetic or syllabic units). The latter result
indicates that, contrary to the prevailing view, the
PT might not be exclusively dedicated to processing
speech sounds. It might instead have a more general
role in processing the abstract properties of language
in multiple modalities. It could also be that auditory
cortex within the STG undergoes functional
reorganization in the absence of auditory input to
respond to complex visual inputs more generally. These
findings therefore raise many interesting questions
concerning the functional role of STG regions in the
deaf.
These new data indicate that the specialization for
language is not pre-specified exclusively by the
mechanisms for producing and perceiving sound but
might also involve multi-modal areas that are
specialized for
processing the patterning of natural languages. It
seems very clear that sign languages might, somewhat
counter-intuitively, hold some of the keys to
understanding the neural basis of human language.
References and links
ORIGINAL RESEARCH PAPER
Petitto , L. A. et al. Speech-like cerebral activity
in profoundly deaf people
processing signed languages: implications for the
neural basis of human
language. Proc. Natl Acad. Sci. USA 97, 13961–13966
(2000) PubMed
FURTHER READING
Hickok, G. et al. The neural organisation of
language: evidence from sign
language aphasia. Trends Cogn. Sci. 2, 129–136
(1998)
WEB SITES
Laura Petitto | Robert Zatorre
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