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The Left Brain May be Your Infection Fighter

Research suggests the hemisphere influences the immune system

MONDAY, May 24, 2004 (HealthDayNews) -- Researchers have long known that different sides of the brain control language versus visual and spatial functions.

Now, it appears that different brain hemispheres have differing effects on the immune system. When right-handed people had a portion of the left side of the brain removed, they became more susceptible to infection, a new study says.

This finding dovetails with previous research that demonstrated that people who had strokes on the left side of the brain also tended to develop more infections.

"It means that there are probably differences in the ways different sides of the brain modulate the immune system," said Dr. Kimford Meador, lead author of the study appearing in the May 24 issue of the Annals of Neurology.

"It's similar to the different roles the two sides have in emotions," added Meador, chairman of neurology at Georgetown University Hospital in Washington, D.C.

And while this new study doesn't seem to have any immediate practical implications, it does open up a multitude of new avenues for research, Meador said. "Eventually there is a practical implication," he said. "Here it's primarily a research question about how the brain and the body interact."

Little is known about the asymmetries of the human brain. Animal studies, however, have shown a connection between different sides of the brain and immune responses.

Meador, in fact, had read a paper by a French researcher who found that putting lesions on one side of a rat's brain had a different effect on the immune system than putting lesions on the opposite side.

"I thought if rats do this, maybe humans do this," Meador recalled.

Such a theory posed some formidable methodological problems, however. "We don't just willy nilly put lesions in human brains," Meador said.

But if people were going to have surgery anyway, it might be possible to observe them before and after, he reasoned.

Meador and his colleagues examined the immune systems of 22 people with epilepsy before and after they underwent surgery to remove small pieces of their brain in an effort to control their seizures.

Patients who had surgery on the left side of their brains demonstrated a decrease in immune function, namely a reduction in the lymphocytes and T-cells that fight infection. Patients who had surgery on the right side of their brains had increased levels of lymphocytes and T cells. The changes were not related to alterations in mood, stress or cortisol hormone levels, the researchers said.

"T-cells and lymphocytes had this diametrically opposite effect," Meador said.

This finding may only be true for right-handed people, however, because the study did not include enough left-handed and ambidextrous people to assess the effect in them.

Histamine skin testing revealed similar asymmetries. People who had had surgery on the right side of their brain had a bigger allergic reaction on the left arm.

A few previous studies have suggested that people who have strokes on the left side of their brain have lower T-cell levels. The new finding suggests these patients may need to be watched more closely for signs of infection, Meador said.

The next step for researchers, Meador said, is to reproduce these results in a larger number of people and to look at different components of immune system functioning.

They also need to discover the mechanism behind these differences. "Understanding that might lead to new ways to approach treatments for different types of immune disorders," Meador said.

More information

For more on right and left brain activity, visit Indiana University or San Diego State University.

SOURCES: Kimford Meador, M.D., professor and chairman, neurology, Georgetown University Hospital, Washington, D.C.; May 24, 2004, Annals of Neurology
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