Science + Technology

UCLA Study Reports Gender Differences in Brain's Response to Pain

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A new UCLA study shows that different parts of the brain arestimulated in reaction to pain depending on gender. The research, whichrepresents the largest gender-comparison study of its kind, focused on peoplewith irritable bowel syndrome (IBS), one of the nation's most common chronicmedical conditions. The findings may help develop and target better treatmentsfor IBS and other illnesses.

"We are finding more scientific differences between men andwomen as we improve research methods and broaden study populations," said studyco-author Dr. Emeran Mayer, UCLA professor of bio-behavioral sciences, andmedicine, physiology and psychiatry. "This growing base of research will helpus develop more effective treatments based on a new criteria: gender."

Dr. Mayer is the director of the new Center forNeurovisceral Sciences & Women's Health (CNS) at UCLA, which conducted thestudy.

Published in the June 2003 issue of the journalGastroenterology, the study examined 26 women and 24 men with IBS. UCLAresearchers took positron emission tomography (PET) brain scans of patientsduring mild pain stimuli.

Although researchers found some overlapping areas of brainactivation in men and women, several areas of male and female brains reacteddifferently when given the same pain stimulus. The female brain showed greateractivity in limbic regions, which are emotion-based centers. In men, thecognitive regions, or analytical centers, showed greater activity.

"The reason for the two different brain responses may dateback to primitive days, when the roles of men and women were more distinct,"said study co-author Dr. Bruce Naliboff, UCLA clinical professor of psychiatryand biobehavioral sciences, and co-director of CNS.

According to Naliboff, these gender differences in brainresponses to pain may have evolved as part of a more general difference instress responses between men and women.Men's cognitive areas may be more highly triggered because of the earlymale role in defending the homestead, where in response to stress and pain, thebrain launched a calculated fight-or-flight reaction. The female limbic regionsmay be more responsive under threat because of their importance in triggering anurturing and protecting response for the young, leading to a more emotion-basedresponse in facing pain and stress.

Naliboff noted that both responses have advantages andneither is better. In fact, under conditions of external threat, the differentresponses may lead to complementary behaviors between men and women.

In addition, researchers found that the anticipation of paingenerated the same brain responses from study volunteers as the actual painstimulus. "The brain is a powerful force in dictating how the body responds topain and stress," said study co-author Dr. Lin Chang, UCLA associate professorof medicine and co-director of CNS.

The next step, according to Mayer, is to look at how theresults of the study may impact treatment for IBS and other disorders. Mayeradds that one current drug for IBS, Lotronex, affects the limbic system and hasworked more successfully in women than men.

UCLA's Center for Neurovisceral Sciences and Women's Healthstudies how the brain, stress and emotions impact the development of disordersthat affect mainly women.

Irritable bowel syndrome affects 15 to 20 percent ofAmericans and causes discomfort in the abdomen, along with diarrhea and/orconstipation.

The National Institute of Diabetes and Digestive and KidneyDiseases and the National Institute of Nursing Research, both part of theNational Institutes of Health, funded the study.

-UCLA-

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