http://www.biosciencetechnology.com/news/2014/11/damage-brain-networks-affects-stroke-recovery?
Initial results of an innovative study may significantly change how some patients are evaluated after a stroke, according to researchers at Washington University School of Medicine in St. Louis.
For more than a century, physicians have made it a priority to
learn where stroke has injured the brain and the extent of the damage.
The new results suggest another question may be equally or more
important: How has the stroke affected the ability of uninjured brain
regions to network with each other?
According to senior author Maurizio Corbetta, MD, the answers to
this question may help physicians more accurately predict the challenges
a patient recovering from stroke may face and guide application of new
approaches for accelerating recovery.
“Studying the way different brain regions connect with each other
as networks appears to be a powerful way of determining the nature and
location of the problems caused by stroke,” said Corbetta, the Norman J.
Stupp Professor of Neurology.
The paper appears online in Brain.
Many hospitals have MRI scanners that can gather information on
brain networks. The expertise needed to use this data to assess network
health is less widely available, but Corbetta expects that to change as
the benefits of this approach become more apparent.
“Understanding whether pathways that appear to be structurally
intact are actually under- or overconnected from a networking point of
view may provide targets for novel treatments,” he added. “One example
is transcranial magnetic stimulation, which uses exposure to strong
magnetic fields to adjust the activity levels of groups of brain
cells.”
The findings come from an ongoing study of stroke patients. Most
stroke research focuses on patients with damage to particular brain
areas, but this study is different. Researchers are enrolling anyone who
recently had a stroke for the first time.
“Our strategy is to enroll anyone with a first-time stroke, no
matter where in the brain their strokes caused damage and no matter what
problems the strokes have caused for the patients,” said first author
Antonello Baldassarre, PhD, now at the University of Chieti-Pescara in
Italy. “We think that makes this study a more relevant representation of
the problems strokes cause for patients.”
In every subject, the researchers assess the size and location of
stroke damage. They use MRI scans to measure functional connectivity, or
the ability of brain regions to communicate with each other in a
coordinated fashion. They also check attention, vision, movement,
language and memory, which often are impaired by stroke. These
evaluations occur two weeks, three months and one year after stroke.
The research analyzes data gathered from 84 patients in the first five years of the study.
Scientists have long thought stroke does most of its damage in the
cortex, the outer layer of brain cells where higher mental functions
occur. But the results suggest stroke causes more harm to the
connections in the white matter, which is underneath the cortex and
connects different parts of the cortex to the cortex and the spinal
cord.
“We think this is why a stroke that damages one part of the brain
can seriously disrupt the function of another, distant part of the
brain,” Corbetta said.
For the analysis, researchers focused on problems with spatial
attention deficits, which affect 250,000 to 300,000 stroke patients in
the United States each year. These impairments include an inability to
notice or respond to stimuli on one side of the body. A male patient
asked to shave his face, for example, might shave only one side of it.
In the patients, the researchers compared changes in functional
connections with the severity of spatial attention deficits 1-2 weeks
after their strokes. They also identified two groups of patients with
similarly placed brain lesions. One group had developed problems with
attention, while another had not.
The scientists could not differentiate between the two groups based
on the physical damage to their brains. But when they tested brain
networking by monitoring patients as they rested in an MRI scanner, a
significant distinction emerged.
“In the patients with spatial attention problems, the connections
between the left and right hemispheres of the brain were decreased in
proportion to the severity of their impairment,” Corbetta said. “But
those same connections were fairly normal in the group that did not have
impaired attention.”
A second abnormal networking pattern also was associated with
impaired attention. Regions in the damaged hemisphere of the brain that
do not normally work together in networks started communicating with
each other after stroke. This abnormal crosstalk was linked to increased
problems with attention.
“Proper balancing of the interactions between different brain
regions appears to be a key component of healthy brain function. You
don’t want these interactions to increase or decrease too much, or
problems will result,” Corbetta said. “Our field is developing novel
strategies that may help restore these imbalances, and looking at the
brain’s functional connections will help us determine where those
techniques should be applied.”
Source: Washington University, St. Louis
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