Washington University. US: Stroke can lead to a wide range of problems such as depression and
difficulty moving, speaking and paying attention. Scientists have
thought these issues were caused by damage to the brain’s “computer
processors” — cells in the brain’s outer layer that do much of the work
involved in higher brain functions.
But a new study by researchers at Washington University School of Medicine
in St. Louis has found compelling evidence that stroke damage to
“cables” buried inside the brain plays an important role in these
impairments. The cables connect cells on the brain’s surface to each
other, to other cells deep in the brain and to cells in the spinal cord
that link the brain to the rest of the body.
“This study provides a new framework to think about the damage caused by stroke,” said senior author Maurizio Corbetta,
MD, the Norman J. Stupp Professor of Neurology. “A more complete and
accurate description of the most common anatomical damage and deficits
after a stroke will help us understand how the brain can adapt to
recover lost functions and potentially lead to new rehabilitation
strategies."
The results appear online March 4 in Neuron.
Neurologists’ traditional approach to stroke originated with Paul
Broca, a French surgeon who in 1861 linked a stroke patient’s severe
speech problems to damage to an area of the cortex, the outer layer of
gray matter that wraps around the surface of the brain. The area Broca
identified is underneath the left temple.
Since then, neurologists have continued in the tradition established
by Broca and have associated different stroke-related problems to damage
in particular areas of the cortex. That has led to the identification
of a hodgepodge of dozens of different stroke-related syndromes that
often are difficult to match precisely to an individual patient’s
symptoms.
With the advent of modern brain scans, scientists later discovered
that stroke only rarely affects the cortex but often involves the tissue
underneath the cortex, which is primarily composed of the fibers
connecting different parts of the brain. In 2007, for example, a team
used MRI to image the brain of Broca’s first patient and found the
stroke had caused significant damage to the white matter.
To get a better sense of how stroke damages the brain, Corbetta and
his colleagues initiated a study of patients who had just suffered
first-time strokes. The new study uses data gathered from 132 patients
treated at Barnes-Jewish Hospital.
In every subject, the researchers used MRI scans of the brain to
assess the extent and location of stroke damage. They also measured
structural connectivity — the connections in the white matter; and functional connectivity —
the ability of brain regions to communicate with each other in a
coordinated fashion. They also examined attention, vision, movement,
language and memory, which often are impaired by stroke. These
evaluations occurred one to two weeks, three months and one year after
each patient’s stroke.
The results show that stroke is more likely to inflict the most harm
in three areas of the brain, all under the cortex: the white matter; the
basal ganglia, which are important in movement and reward; and the
thalamus, which regulates sleep and consciousness, and plays roles in
vision, hearing and touch.
The researchers also found that deficits after stroke are better
described by three groupings rather than by many individual deficits.
The first group was associated with problems with language and memory;
the second was linked to problems with vision, left body movement,
general attention and awareness of the left side of space; and the third
was linked to problems with right body movement and awareness of the
right side of space.
The combination of deficits across many patients was not due to the
extent of damage caused by the strokes but to damage of white matter
“crossroads,” regions with fibers that have many connections. According
to Corbetta, these lesions affect communication across many brain
regions, which helps explain why the damage they produce causes such a
diverse array of symptoms.
“The majority of research in stroke, including funding at the
National Institute of Health, has focused on the cortex," Corbetta said.
"Our results show the importance of loss of connections due to white
matter damage, and highlight the need to look at the impact of stroke on
the ability of undamaged brain regions to communicate. Future studies
should focus on how the stroke affects brain function. This should be
very helpful in diagnosis and treatment of these patients.”