The headaches returned during that break, but they were less frequent and easier to tolerate. The forgetfulness was still alarming, but she knew she had access to help. The calm of her new life, with entire days spent in her dimly lit, quiet apartment, had smoothed out her symptoms. But she also knew they could flare up under stress and overstimulation. On one of these occasions, last June, her baby had a bad fever, and Becky rushed her to the emergency room. There were forms and questions and grating beeps blaring from the monitors while the baby wailed on the bed. The lights above were a brash fluorescent, the worst kind for a person with a brain injury. In the emergency room, Becky felt pressure mustering behind her temples and forgot some simple words. “I need to know my … ” she trailed off for several seconds. “Choices.”

Almost everything we know about concussions and neurodegenerative disease comes from studying male brains. But some of the research we do have, mostly on athletes’ brains, suggests that women may be more vulnerable to concussions than men. Concussions jostle the brain’s gelatinous mass of neurons, disrupting circuitry that affects mood, function, thinking and more. Men tend to have more muscular necks that better cushion acceleration of the head. There are anatomical differences between male and female axons, too. Women’s axons — nerve fibers that unfurl between neurons to form communication networks — have a generally leaner architecture that could shear more easily during trauma. Successive concussions may tear them, releasing tangles of tau protein into the brain. But the differences are more than mechanical.

When Ramesh Raghupathi, a professor of neurobiology and anatomy at Drexel University College of Medicine, began studying concussions in female rats, he immediately noticed differences from those of males. The cellular changes looked similar, but functionally, the rats experienced different outcomes: The females experienced more intense anxiety and depression. “It had to do more with the circuitry and neurochemistry of the female brain compared to the male brain,” he says. “You cannot discount the role of sex hormones.”

In a 2014 study, researchers found that women of childbearing age experienced worse post-concussive symptoms than postmenopausal women or women taking hormonal birth control, especially when the concussion occurred during the luteal phase of the menstrual cycle (after ovulation, before the period begins). Progesterone levels are high during this time, and one theory is that progesterone disruption, perhaps caused by harm to the pituitary gland, could have an especially harsh impact on neurons. In other words, where a victim is in her menstrual cycle at the time of impact could have a significant effect on the outcome of her traumatic brain injury.

A study published last year analyzed female athletes during the immediate aftermath of concussions. Researchers measured levels of progesterone and noted menstrual phases at the time of injury. Their results were consistent with the association of progesterone disruption and poorer outcomes, though more data is needed to understand why. (An estimated 31 to 50 percent of transgender people experience intimate-partner violence, with higher numbers for transgender women, but no studies have analyzed the impact of brain injuries in this group.)

“So much money goes into investigating concussions in sports that those protocols and papers go on to shape the way concussions in general are thought about,” says Stephen Casper, a historian of neurology at Clarkson University. “There’s no money to be made from studying intimate-partner abuse.” When it comes to chronic neurodegenerative diseases like C.T.E., even less is known about what women may face after decades of abuse. Slight acceleration or shaking of the brain that doesn’t register as a concussion may, if repeated frequently enough, trigger a cascading, dementia-like disease process that continues years after the trauma stops and is discovered only through postmortem examination.

At the VA-BU-CLF Brain Bank in Boston, the world’s first C.T.E.-focused brain repository, Ann McKee, the director, has collected around 1,250 specimens. Her findings have helped change the way football is played and has helped move hundreds of millions of dollars toward victim compensation, pushing the neurological hazards of contact sports squarely into public consciousness. But 14 years after the bank’s founding, nearly all of its specimens are still male. Female brains, McKee says, are hard to find, especially from women like Becky. “When you’ve got an interpersonal-violence situation, you have to get permission from the next of kin to get a brain donation,” she says. Domestic violence carries a shame that can be hard for families to confront, and if the next of kin is the abuser, there’s virtually no chance.