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Study Offers Insights Into Sensory Perceptions

Woman who suffered stroke starting experiencing sounds as bodily sensations

MONDAY, Sept. 24, 2007 (HealthDay News) -- By studying a woman who experienced sounds as bodily sensations after suffering a small stroke, researchers think they've gained new insight into how the brain processes sensory signals and fixes itself when injured.

The woman began having strange reactions to sound after suffering a stroke that only affected part of a brain structure known as the thalamus. Her experiences provide more evidence that the brain tries to repair itself by making new neural connections after injury, said study lead author Tony Ro, an associate professor of psychology at Rice University.

"It tells us that the brain can continue to reorganize and alter its function very late into life," Ro said.

The thalamus, located in the middle of the brain, acts as a kind of relay station for sensory processing, Ro said. "Almost all of the sensory receptors from the eyes, ears or skin go through into the thalamus before they project onto higher areas of the brain."

About eight years ago, the woman suffered a small stroke that affected only the ventrolateral nucleus, a part of the thalamus that is smaller than a pea, Ro said. She's now about 40 years old and works as a college professor.

The stroke cut off blood circulation "and left a little tiny hole in her brain which was no longer functioning," he said. "About a year to two years after her stroke, she began feeling a lot of odd sensations in the left half of her body when different types of sounds were played."

The study authors then gave a variety of neurological tests to the woman. Some sounds would cause sensations in her left hand, the left side of her face or her left forearm, a phenomenon known as synesthesia, Ro said. Other sounds did nothing.

It appeared that the brain's neurons were reconnecting after the stroke and causing "changes in behavior, sensory processes and perception," Ro said. "Areas of the brain that were primarily involved with feeling on the left half of her body that are no longer receiving input due to brain damage can now respond to different sounds."

The study was expected to be published in an upcoming issue of the journal Annals of Neurology.

Dr. Richard E. Cytowic, a Washington, D.C., neurologist who studies synesthesia, said the study is useful, because the brain scans done by the researchers allowed mapping of cellular connections between the dead area of the woman's brain and other areas of the brain.

And, even though it's just one case, the study "forces rethinking of how the thalamus and brain are organized," Cytowic said. "The areas so often talked about and pointed to on brain diagrams are not so distinct and isolated as conventional illustrations claim."

More information

Learn more about synesthesia from Massachusetts Institute of Technololgy.

SOURCES: Tony Ro, Ph.D., associate professor of psychology, Rice University, Houston; Richard E. Cytowic, M.D., neurologist, Washington D.C.; Annals of Neurology
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