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By
Michael Purdy
March
14, 2007 -- Neuroscientists at Washington University
School of Medicine in St. Louis have linked a common
post-stroke disability to impaired communication between
brain regions.
In
the March 15 issue of Neuron, researchers report a tight
correlation between the degree to which communication
was blocked and the severity of patients' symptoms.
This led them to suggest that testing for such communication
breakdowns could greatly improve clinical assessment
and treatment of stroke and other brain injuries.
"For
more than a century, we have linked neurological deficits
and their recovery to the damage done to neurons directly
affected by a stroke or other injury," says senior
author Maurizio Corbetta, M.D., the Norman J. Stupp
Professor of Neurology. "However, we are learning
that a lesion in one part of the brain can impair the
function of brain regions not directly harmed by the
lesion. We need to promote use of this more dynamic
view of brain changes after damage."
Researchers
studied both healthy volunteers and a group of 11 patients
who had a stroke on the right side of the brain between
the ear and temple. Every year, strokes in this area
leave three to five million patients with a condition
called spatial neglect. Patients have trouble paying
attention to one side — they may seem to be unaware
of their left arm, for example, fail to shave the left
side of their face or leave boxes blank on the left
side of a form. The condition is most severe in the
first few months following a stroke, but in some patients
it becomes a chronic problem.
For
the study, scientists had patients and healthy volunteers
indicate whether they could see an asterisk on the left
or right side of a video screen. While they did this,
their brains were scanned using functional magnetic
resonance imaging (MRI). Researchers then applied an
approach known as functional connectivity to the results.
"Functional
connectivity MRI examines correlations between spontaneous
activity in different brain regions, providing a peek
into the fundamental architecture of the brain,"
says lead author Biyu He, a graduate student in neurosciences.
Patients'
brains were scanned within a month of their stroke and
again more than six months later, when the symptoms
of spatial neglect often have started to fade. Scientists
paid particularly close attention to the connection
between two brain networks that help control attention,
or what part of the continual stream of sensory inputs
the brain most tightly focuses on.
Researchers
found a consistent link between the severity of spatial
neglect symptoms and the degree of impairment in communication
within and between those two networks.
The
results further reinforce a theory about the effects
of brain injury that Corbetta and his colleagues have
been building for years. According to the theory, brain
injury can damage give-and-take processes between brain
regions that are essential for the regions' proper function.
Regardless of whether damage directly strikes a brain
region in the network or disables circuitry connecting
the regions, the net effect leaves one or more brain
areas stranded like the sole occupant of a seesaw, unable
to operate effectively without its missing partner.
Follow-up
studies are planned to see if other stroke-induced deficits,
such as the loss of language ability known as aphasia,
are linked to similar disruptions of communication between
brain regions.
"This
approach may be helpful for other conditions in which
functional communication is disrupted, such as traumatic
brain injury, multiple sclerosis and Alzheimer's disease,"
Corbetta says.
He
BJ, Snyder AZ, Vincent JL, Epstein A, Shulman GL, Corbetta
M. Breakdown of functional connectivity in frontoparietal
networks underlies behavioral deficits in spatial neglect.
Neuron, March 15, 2007.
Funding
from the National Institute of Mental Health, the National
Institute of Neurological Disorders and Stroke and the
James S. McDonnell Foundation supported this research.
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