Blow your mind � but keep to the right

Left brain damage hurts the immune system
but a blow to the right brain boosts it

By Henry Peters

Just when you think that you're finally getting the hang of this medicine thing, along comes a completely baffling finding that should restore your faith in our fundamental ignorance of what the human body is really up to. People who suffer damage to the left side of their brains are susceptible to a dangerous collapse in immune response � if they are right-handed. As if that weren't weird enough, right-handed people who suffer damage to the right side of their brain may well enjoy a significant boost to their immune system.

The findings, reported May 24 in the online edition of the Annals of Neurology, don't come as a total surprise. After all, patients who suffer a left-sided stroke are sometimes more susceptible to later infection.

The authors of the current research have been investigating the differential relationships of the two brain hemispheres to the immune system for several years, since animal studies first showed that the two sides weren't hooked up in the same way.

Cerebral resection, as a treatment of last resort for refractory epilepsy, provided the perfect opportunity to check the hypothesis of hemispherical immune differences. This study tested 22 patients who underwent cerebral resections limited to one hemisphere.

They found that most patients who underwent left-sided surgery showed a significant decline in lymphocytes, total T cells, and helper T cells. Those who underwent right-side surgery mostly exhibited significantly greater numbers of these immune cells in the aftermath.

These changes translated into real differences in immune performance. Patients who endured left hemisphere surgery showed altered histamine skin response ratios and reduced flare skin responses. Conversely, patients who had undergone right hemisphere resection had stronger flare skin responses.

There is one important caveat to the results. With only 22 patients in the trial, and nearly all of those right-handed, the authors were unable to make any guesses at all as to whether left-handed patients would show the same response, no response, or a mirror-image response.

What does it all mean? Essentially, nobody has the foggiest idea. "The immune and nervous systems are interlinked, influencing each other in complex ways that we are just beginning to understand," said study director Dr Kimford Meador, of Georgetown University Hospital in Washington. "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."

One important conclusion may be drawn, however. "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 Dr Meador.