Reorganization of the Brain Allows Blind Individuals to Process Speech More Effectively
The portion of the brain devoted to vision may play a prominent
role in processing the spoken word in blind people. Research conducted
by the NIH’s National Institute of Neurological Disorders
and Stroke (NINDS) shows that the "sight" region of the
brain is essentially reorganized in blind individuals to help them
process spoken words more effectively. Findings yield important
information about the brain’s ability to compensate for lost
function. The study appears in the October 3, 2004 online issue
of Nature Neuroscience1 and in the
journal’s November issue.
The research involved nine people who are either congenitally blind
or who lost their sight before age 4 and nine sighted individuals
who served as controls. NINDS investigators Amir Amedi, Ph.D., and
Agnes Floel, M.D., spoke a noun out loud and then instructed each
study subject to respond with an appropriate verb as quickly as
possible, before the next noun was spoken 5 seconds later. Short
bursts of repetitive transcranial magnetic stimulation (rTMS) —
which uses a pulsed magnetic field directed by a special coil to
influence electrical activity in the brain — were delivered
to three sites in the brain’s sight region, plus one non-sight
control region, immediately after the noun was spoken. The rTMS
pulses were designed to create a transient "virtual lesion"
in the stimulated areas that would disturb the subject’s ability
to come up with an appropriate verb.
The investigators found that rTMS of a region in the brain called
the "occipital pole" affected the ability of blind patients
— but not sighted patients — to come up with a verb
during the language task. The stimulation particularly affected
the blind subject’s ability to understand and respond to the
spoken noun. The finding is the first of its kind to show the relevance
of the brain’s visual cortex in language processing in blind
individuals, who must process words without any visual clues. This
research demonstrates that the visual cortex, normally responsible
predominantly for sight, can help the brain to process other senses
and types of activities.
"Verbal processing in the blind is mediated by the interplay
of a network of areas, including the occipital pole and the prefrontal
cortex," said Leonardo G. Cohen, M.D., chief of the NINDS Human
Cortical Physiology Section. "Our finding shows that the occipital
cortex of blind subjects is recruited to be part of the network
involved in performing high-level cognitive functions such as speech
"This study provides an exciting, new insight into how the
brain reorganizes following loss of nerve function," said
Story C. Landis, Ph.D., NINDS director. "Additional research
on brain plasticity may eventually lead to treatments promoting
functional recovery following stroke or other neurological diseases."
Future studies are planned to determine if this form of plasticity
is also possible in people who become blind later in life.
The NINDS is a component of the National Institutes of Health within
the Department of Health and Human Services and is the nation's
primary supporter of biomedical research on the brain and nervous
This release will be posted on EurekAlert! at http://www.eurekalert.org
and on the NINDS website at http://www.ninds.nih.gov/news_and_events/index.htm.
Amedi A, Floel A, Knecht
S, Zohary E, Cohen, LG. “Transcranial magnetic stimulation
of the occipital pole interferes with verbal processing in blind
subjects.” Nature Neuroscience, Vol. 7, Issue 11.