Neurons Different in Left, Right Brain Structure
United Press International

September 15, 2000

WASHINGTON, Sept. 15 (UPI) -- Scientists in Germany have found that two structures in the brain-one left, one right-may look the same to the naked eye, but their individual neurons appear pronouncedly different under the microscope.

The finding could be the first step toward unraveling the cellular "wiring" of different parts of the brain, and might ultimately help doctors determine what goes wrong in conditions such as autism and Alzheimer's disease, said neurology experts.

According to Michael Gazzaniga, professor of cognitive neuroscience at Dartmouth University, Hanover, New Hampshire, the painstaking discovery is the first evidence of cellular differences between corresponding structures on the right and left sides of the brain that appear identical anatomically but behave differently.

The key is likely their difference in function. The brain structure, called Brodmann's area 22, is critical for generating and understanding individual words on the left side. On the right, however, it helps discriminate between melody, pitch, and sound intensity, he explained.

Gazzaniga wrote an editorial about the study, which appears in the current issue of the journal Science.

To conduct their study, lead author Ralf A. W. Galuske and his colleagues at the Max Planck Institute for Brain Research in Frankfurt examined the brains of six men and one woman, ranging in age from 34 to 82, who had died 18 to 24 hours before.

From each brain they took tissue samples from a region known as Brodmann's area 22 from both the right and left sides of the brain. Then they injected each sample with a special dye that revealed the interconnections among the neurons in those areas.

The neuron clusters comprising each area were similar in size, Galuske and co-workers found. What varied were the distances between the clusters: on the left, they were about 20 percent farther apart, with more fiber connections among the cells and a more complex cellular architecture.

"These interconnections suggest an underlying difference as to why that part of the brain is active in processing language," Gazzaniga told United Press International. "This is a quantum jump forward-it's really going to push research along fast."

"This study clearly demonstrates that an area associated with speech processing differs from the same area on the other side of the brain," added Jeffrey Hutsler, assistant professor of psychology at the University of Michigan, Ann Arbor.

Hutsler called the study "heroic" because the investigators had to allow four to six months for the dye to stain the brain specimens completely, with no guarantee of obtaining significant results.

In children who have had their left hemispheres removed because of injuries or to treat diseases such as epilepsy, "the right hemisphere steps up to the bat" to compensate for language ability, Hutsler explained. However, these patients have lingering deficits in their ability to understand complex sentences.

"From a clinical standpoint, this study shows that there may be some critical organizational areas that help people achieve complete functionality, which might have implications for people who have lost some of these language areas." One question that remains is, "how much of language ability is built in, and how much is the result of interaction with the environment?"

Various scanning techniques have already shown that when appreciating speech, for example, nerve cells in the left brain fire harder, said pharmacologist Desmond Smith of the University of California, Los Angeles, School of Medicine.

"But these imaging techniques don't show what is happening at the level of the nerve cell," he said. "This paper provides a very careful microscopic evaluation of the same part of the brain in the right and left hemispheres."

Studying differences in gene expression throughout the brain will add to the light shed on the microscopic differences in anatomy associated with various functions and could eventually help doctors understand what goes wrong in certain diseases, Gazzaniga said.

He explained: "If we begin to learn the normal wiring patterns of the human brain and combine that with gene expression, then you can start tackling diseases and ask what's wrong with these brains."

(Reported by Norra MacReady in Los Angeles.)
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