A number of experts at the conference speculated as to why the young brain seems to be particularly susceptible to SIS. Dr. Hovda pointed out that the human brain does not reach maturity until well after 20 years of age. The young brain has a higher concentration of water, he explained, which makes it more difficult to compress when catastrophic brain swelling occurs in SIS. The continual expansion of the brain within the small confines of the skull results in the death of brain tissue.
Dr. Hergenroeder noted that a child’s brain may also be more susceptible to SIS because it fits more tightly inside the skull than an adult’s brain. The tighter fit of a child’s brain means there is less reserve to accommodate the increased volume when an injury causes the brain to swell.
There are also findings to suggest that the brain of youngsters may be more susceptible to long-lasting brain damage following just one concussion. This damage might hamper their ability to learn.
Dr. Hovda found that when he raised rat pups in a stimulating environment, the portion of their brains responsible for higher thinking functions expanded. These rats become smarter, as seen by the smaller amount of time they need to complete a maze, compared to those raised in a relatively boring environment, Dr. Hovda said. But if these young rats experience a mild concussion, they lose the ability to learn from an enriched environment and to become smarter. Their brains resemble those of otherwise similar mice raised in the normal banal environment, and they take as long as them to complete a maze. “The take-home message from this study is that, at least in animals, traumatic head injury early in life does not create a lot of deficits if it is done by a very mild injury,” said Hovda. “But it does seem to come with a cost—a developmental reduction in [the brain’s ability to] take in information from the outside world.”
Dr. Echemendia found that recently concussed adolescent athletes also tended to do poorly on tests that measured their ability to learn new information.
Akin to what Dr. Hovda found in his rats, Dr. Echemendia found that recently concussed adolescent athletes also tended to do poorly on tests that measured their ability to learn new information. These deficits disappeared over a short period of time. Jon Almquist, one of the participants at the conference, pointed out that concussed youngsters sometimes have difficulty learning during the ten days or so that it takes them to recover from their concussions, so even short-term deficits may affect school performance.
Dr. Brooks added that it was important to keep in mind that any brain impairment stemming from concussions or heading in children or adolescents will affect their academic performance as well as their athletic performance. “We are not dealing necessarily with professional athletes, where this is their livelihood,” she said. “The majority of high school and collegiate athletes will not go on to play at an elite level, and they are students as well as athletes.”
Intriguing animal research findings presented at the conference by neuropharmacologist Dr. Robin Roof might explain why SIS appears to mainly afflict males. She found that the hormones, estrogen and progesterone, seem to protect rodents from brain damage after they experienced head injury. These hormones are present in higher amounts in adolescent girls and women compared to adolescent boys and men. If they play the same protective role in humans as they do in rodents, Dr. Hergenroeder noted, that could explain why teenage girls and women do not appear as susceptible to SIS.
Dr. Roof noted, however, that there have been conflicting findings as to whether girls and women suffer less brain damage following a blow to the head than their male counterparts. Studies suggest women have a lower threshold for reporting injury and symptoms, and for experiencing certain symptoms such as headache, Dr. Brooks reported. These factors may mask the hormonal effects on brain injury in people to some degree.
“I think what we can say is that these hormones definitely have some sort of neuro-protective effect,” said Dr. Roof. “Whether they play the same role in humans and animals hasn’t been shown scientifically, but I think that they do.”
These findings do not suggest that “our girls are protected enough to not worry about head injury because of these mechanisms,” cautioned Dr. Roof. But she added that estrogen and progesterone or information on how they protect against brain damage might lead to effective treatments for head injury.