Damage to the left half side of brain may make a right-handed person more susceptible to infection

A major immunological difference between the opposite halves of the human brain is now confirmed in a study published May 24, 2004 in the online edition of the Annals of Neurology. Researchers have found that damage or surgery to the left half of the brain may make a right-handed person more susceptible to being immunocompromised.

The results might help to explain intriguing earlier findings that suggested people who had strokes on the left side of their brains were more susceptible to infections.

"These findings raise the possibility that doctors need to be more aggressive in protecting patients from infection following strokes or surgery on the left side of the brain," said study director Kimford J. Meador, MD, of Georgetown University Hospital in Washington, D.C.

Are you a right-brain person—creative, emotional, big picture—or a left-brain person—logical, detail-oriented, practical?

The idea that the two halves of our brains are fundamentally different has settled comfortably in our imaginations, thanks equally to science fiction and self-help books. But beyond a predominant role in language for the left half, scientists have had a hard time pinning down what these differences mean for how our brain works.

Animal studies have shown distinct differences in how the two brain halves are linked to the immune system. Several years ago, Meador and his colleagues found preliminary evidence of similar differences in humans, which could be of great significance for medicine.

"The immune and nervous systems are interlinked, influencing each other in complex ways that we are just beginning to understand," said Meador.

In the present study, the researchers examined how the immune system responded to surgery on either side of the brain, following the progress of 22 epilepsy patients who had parts of their brain surgically removed in an attempt to control debilitating seizures.

Most patients who had surgery on the left side of their brains experienced significant decreases in immune function, with the immune system reducing the numbers of critical disease-fighting cells called lymphocytes and T-cells. By contrast, patients who had surgery on the right side of their brains saw the levels of their lymphocytes and T-cells significantly boosted.

It is important to note that this may be true only for right-handed patients, write the authors. Although they did not have enough left-handed and ambidextrous people in their study, the researchers note that non-right-handed people could have the opposite reaction. Or they might show equivalent immunologic responses to right and left brain injuries.

"Even with these results, we and others have examined only a small portion of possible immune responses in regards to left/right brain influences. Even more important, exactly how the brain alters immune response is unclear. Future studies will need to address these issues," said Meador.

Article: “Role of Cerebral Lateralization in Control of Immune Processes in Humans,” Kimford J. Meador, David W. Loring, Patty G. Gray, Sandra W. Helman, Blanca R. Vazquez, and Pierre J. Neveu; Annals of Neurology; Published Online: May 24, 2004 (DOI: 10.1002/ana.20105).

The Annals of Neurology, the preeminent neurological journal worldwide, is published by the American Neurological Association, the world's oldest and most prestigious neurological association. The 1,400 members of the ANA--selected from among the most respected academic neurologists and neuroscientists in North America and other countries--are devoted to furthering the understanding and treatment of nervous system disorders. For more information, visit http://www.aneuroa.org.