Karen L. Wooley, Ph.D.
Her nanoparticle research has many applications
|
Karen L. Wooley, Ph.D. Her nanoparticle research has many applications |
|
|
|
|
|
|
||||||
|
|
|||||||||||||||||||||||||||||
|
 |
|
After stroke, right side of brain learns language skills
By Gila Z. Reckess When a stroke affects the language areas in the left side of the brain, the right side takes over and learns how to perform language tasks, according to research in the School of Medicine. The study, which appears in the Sept. 26 issue of Neuron, found that the right side of the brain is more active than normal during a verbal language task, and that the right side's activity decreases with practice, similar to what happens on the left side of the brain in healthy individuals. "This is the first demonstration that learning and, by extension, speech therapy change the way compensatory pathways in the brain work," said Maurizio Corbetta, M.D., head of stroke and brain injury rehabilitation. "This study supports the hypothesis that brain pathways in the right hemisphere are directly involved in the recovery of language after stroke." Corbetta, the study's senior author, also is an associate professor of neurology, of radiology and of anatomy and neurobiology. The first author is Valeria Blasi, M.D., a former post-doctoral fellow in neurology in the medical school now at the San Raffaele Scientific Institute in Milan, Italy. Each year, about 750,000 Americans suffer a loss of blood flow to the brain, a condition known as an ischemic stroke. Since the left side of the brain houses most of the areas responsible for speech and language, a left-sided stroke often causes language problems, a condition known as aphasia. About 1 million people in the United States have aphasia, resulting in an estimated $1.5 billion of lost productivity and other costs each year. Remarkably, many of those who initially lose language abilities after a stroke significantly recover these abilities within six to 12 months. Several studies suggest that language recovery occurs because the right hemisphere of the brain compensates for the loss of the left hemisphere. To test whether there is a direct link between recovered language abilities and activity in the right hemisphere, Corbetta's team compared performance scores and brain images from 14 healthy individuals with those of eight stroke patients. The patients all had experienced a stroke at least six months before participating in the study and still had damage near a brain region called Broca's area, which is located toward the front of the brain and thought to be involved in speech. The team first measured the two groups' performance during a word-stem completion task. Participants saw three letters at a time and were asked to say a word that began with those three letters. Each word stem appeared several times during the experiment. The patient group was slower and less accurate, but both groups learned and improved at the same rate. Each group was about 400 milliseconds faster on the seventh block of trials than on the first. Participants in each group also repeated the same answer for a given word stem about 20 percent of the time, a sign that they remembered the word and learned the answer. Participants then performed the same task while undergoing functional magnetic resonance imaging. These images identify which brain regions are active during a given task. Because the task becomes familiar, the brain does not have to work as hard. With practice, brain activity normally decreases in areas that are important for performing the task. In this study, as healthy participants' performance improved, language areas on the left side of the brain, including Broca's area, became less active. In addition, areas toward the back of the brain that are involved in vision became less active in both the left and right hemispheres. Brain images from stroke patients revealed several differences. Language areas damaged by the stroke were not active during the language task. However, areas on the right side of the brain opposite the damaged areas on the left became active, and that activity decreased with practice. Visual areas on the right side also decreased with practice. Patients with smaller lesions had slightly different patterns of brain activity. In addition to learning-related changes on the right side of the brain, the areas near the lesion on the left side also improved with practice. These patients were better at learning the task and ultimately recovered more than the other stroke patients. According to Corbetta, these results indicate that a stroke produces complex changes in the way both sides of the brain perform during language tasks. "This information has direct implications for optimizing rehabilitation and pharmacological treatment after stroke," he said. |
|
||||||||||||||||||||||||||
|
|
