CINCINNATI--Scientists have found that the site in the brain thatcontrols language in right-handed people shifts with aging--a discoverythat might offer hope in the treatment of speech problems resultingfrom traumatic brain injury or stroke.
The shift was documented by researchers led by Jerzy Szaflarski, MD,PhD, assistant professor in the Department of Neurology at theUniversity of Cincinnati (UC) Academic Health Center, and ScottHolland, PhD, professor in the UC departments of biomedicalengineering, pediatrics and radiology. Dr. Holland also heads thePediatric Brain Imaging Research Program at Cincinnati Children'sHospital Medical Center.
Their results will be published in the February 2006 edition of the journal Human Brain Mapping.
While the site of language activity in right-handed people isoriginally the left side of the brain, the researchers report, startingas early as age 5 language gradually becomes a function shared by bothsides. Between the ages of about 25 to 67, the site becomes more evenlydistributed, until language activity can be measured in bothhemispheres simultaneously.
This, the researchers say, may explain why young children whohave had a large portion of one side of the brain surgically removedoften recover completely.
"This knowledge may give new hope for rehabilitation of brainfunction in adults after stroke or traumatic brain injuries," said Dr.Szaflarski. "The fact that language adaptability is seen even in theolder people supports the notion that these patients can berehabilitated and returned to productive life, possibly even after adevastating stroke."
Scientists have long thought that the hemisphere or side ofthe brain that controls language and speech is determined before birth.Most people are right-handed and demonstrate more activity duringlanguage or speech in the left hemisphere of the brain. In left-handedpeople language centers are located more symmetrically.
Drs. Szaflarski and Holland studied brain activity in 177right-handed children and adults aged 5 to 67 at Cincinnati'sUniversity Hospital and Cincinnati Children's using functional magneticresonance imaging (fMRI). The technique shows brain activity, in thiscase language tasks such as reading or speaking, in a specific color.
"Our research revealed that language activity in the brainincreases in the dominant hemisphere from age 5 until about 25," Dr.Szaflarski said, "which may be related to improving linguistic skillsand maturation of the central nervous system.
"We observed that the nondominant side of the brain startedhelping the dominant side during reading or speaking from the age of 25to 67," Dr. Szaflarski continued. "It's possible that as cognitivesystems began to fail in the dominant side of the brain, the other sideor hemisphere needs to compensate. Our study showed that older peoplehave a more balanced capacity for language, with activity on both sidesof the brain."
From around age 5 until about 25, said Dr. Szaflarski, languagecapacity in right-handers grows stronger in the left hemisphere of thebrain. Similarly, fMRI shows increasing brain activity in the righthemisphere of left-handed persons until age 25.
"We were most interested in why this occurs, and the age atwhich the hemispheric language dominance began to decrease," said Dr.Szaflarski.
Drs. Szaflarski and Holland and their colleagues are alsoinvestigating how the brain handles language when it is damaged by astroke or traumatic brain injury.
In children, Dr. Szaflarski said, the brain seems able toreorganize and shift the work load to the uninjured side. In adults,this doesn't happen as easily.
With a view to developing better treatment for brain injury inchildren and adults, the researchers are now trying to learn at whatage this transition occurs.
Dr. Szaflarski and Dr.Holland's research is funded by the National Institutes of Health andthe Neuroscience Institute of Cincinnati, a center of excellence inneuroscience specialties at the University of Cincinnati College ofMedicine and University Hospital. The Neuroscience Institute, of whichDr. Szaflarski and Dr. Holland are members, is dedicated to patientcare, research, education and the development of new medicaltechnologies that may help patients with stroke, epilepsy, multiplesclerosis, trauma, Alzheimer's disease, Parkinson's disease and othermovement disorders.
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