Brain Injuries Found to Differ in Sexes

As if it weren't already hard enough to understand the opposite sex, scientists have discovered another way that men and women are different–the way that their brains respond to injury.

Scientists from Lawrence Berkeley National Laboratory and UC San Diego found that women fifty years old and younger were more likely to experience brain swelling than men of the same age group.

After the age of fifty, however, women fared better than men, a shift that the researchers attributed to hormonal changes at menopause, the stage in a woman's life when monthly periods end.

Men do not experience an analogous hormonal change.

"The rate of decline of the male sex hormones is very individual and very slow," said Anat Biegon, a scientist at Berkeley Lab who was an author in the study.

Further investigations could lead to brain injury treatment programs that account for sex differences.

The new analysis confirmed a changing attitude in neuroscience.

"This was surprising because the dogma in the field is that women do better than men after brain injury," said Biegon. "The consensus was that women are much more likely to preserve language function after strokes and brain injuries than men."

Talking better does not necessarily mean swelling less, however.

While language capacity is more localized in one hemisphere of a man's brain, "language is represented in women on both sides of the brain," Biegon said.

Anat Biegon

Therefore, a brain injury that disproportionately affected one side of the brain is more likely to render a male victim speechless.

However, a female victim of a comparably severe injury is more likely to experience a swollen brain.

Although a bigger brain may sound appealing when studying in the library the night before a midterm, it can be deadly when lying on a hospital bed.

"Brain swelling brings about hypertension (abnormally high blood pressure) because the brain is confined in a very rigid space (the skull) and cannot expand outwards, so pressure builds up inside the brain instead," Biegon said.

While a lump on the forehead can simply expand outwards, a swelling brain has nowhere safe to go.

"The only way 'out' is at the base of the skull, where the brain stem, which controls vital functions, herniates, causing death," Biegon said.

A hernia occurs when part of an organ or tissue–the brain stem in this case, protrudes out of the lining that normally contains it.

Trying to understand how to counteract this morbid process, the researchers are conducting a new human study in which they will monitor the levels of the hormones estrogen and progesterone in female patients, and the levels of testosterone in male patients.

Administering the female hormone progesterone has been shown to be beneficial in animal studies.

The data analyzed by the researchers was actually collected previously for a clinical trial of a prospective brain injury drug, tirilazad mesylate.

A previous sex-related analysis of the data had shown no differences between the brain swelling of male and female brain injury patients.

However, by breaking up the data by age, the Lawrence Berkeley and UC San Diego researchers were able to detect a sex difference, presumably related to hormones.

Nonetheless, Biegon was wary of hastily applying a hormone treatment to human subjects.

"Tirilazad mesylate was one of five drugs that worked in the animal models but failed miserably in people," Biegon said. "It is important to look at things within a human context."

Because "trying everything can make things worse," Biegon urged doctors to remember their creed: "Do no harm."

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