Bernick does believe that there's now enough evidence to suggest real differences between the ways men and women respond to head injuries.

"Women may be more likely to suffer concussion. Their symptoms may linger longer," he says. "The question is: Is that because women are just more likely to report injuries, or is there a biological higher vulnerability."

Researchers have suggested some reasons women might be more vulnerable. They tend to have weaker neck muscles. So a head impact might shake the brain more violently. And hormonal differences might affect the brain's response to an impact or injury.