|
 Stroke
damage keeps brain regions from 'talking' to
each other
Newswise — 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 func 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.
Washington University School of Medicine's
full-time and volunteer faculty physicians also are the medical
staff of Barnes-Jewish and St. Louis Children's hospitals. The
School of Medicine is one of the leading medical research, teaching
and patient care institutions in the nation, currently ranked fourth
in the nation by U.S. News & World Report. Through its affiliations
with Barnes-Jewish and St. Louis Children's hospitals, the School of
Medicine is linked to BJC HealthCare. |