The shift was documented by UC
researchers led by Jerzy Szaflarski, MD, PhD, of the Department of
Neurology, and Scott Holland, PhD, of the departments of biomedical
engineering, pediatrics and radiology. Dr. Holland also heads the
Pediatric Brain Imaging Research Program at Cincinnati Children's
Hospital 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 is originally the left side of the brain, the
researchers report, starting as early as age 5 language gradually
becomes a function shared by both sides. Between the ages of about 25
to 67, the site becomes more evenly distributed, until language
activity can be measured in both hemispheres simultaneously.
This, the researchers say, may explain
why children who have had a large portion of one side of the brain
surgically removed often recover completely.
"This knowledge may give new hope for
rehabilitation of brain function in adults after stroke or traumatic
brain in-juries," says Dr. Szaflarski. "The fact that language
adaptability is seen even in the older people supports the notion that
these patients can be rehabilitated and returned to productive life,
possibly even after a devastating stroke."
Scientists have long thought that the
hemisphere or side of the brain that controls language and speech is
determined before birth. Most people are right-handed and demonstrate
more activity during language or speech in the brain's left hemisphere.
In left-handed people language centers are located more symmetrically.
Drs. Szaflarski and Holland studied brain
activity in 177 right-handed children and adults, aged 5 to 67, using
functional magnetic resonance imaging (fMRI). The technique shows brain
activity, in this case language tasks such as reading or speaking, in a
"Our research revealed that language
activity in the brain increases in the dominant hemisphere from age 5
until about 25," Dr. Szaflarski says, "which may be related to
improving linguistic skills and maturation of the central nervous
From around age 5 until about 25, says
Dr. Szaflarski, language capacity in right-handers grows stronger in
the brain's left hemisphere. Similarly, fMRI shows brain activity
increasing in the right hemisphere of left-handed persons until age 25.
Drs. Szaflarski and Holland and their
colleagues are also investigating how the brain handles language when
it is damaged by a stroke or traumatic brain injury.
In children, Dr. Szaflarski says, the
brain seems able to reorganize and shift the work load to the uninjured
side. In adults, this doesn't happen as easily.