CONCUSSION IS A BRAIN INJURY

The spectrum of concussion signs and symptoms and their seriousness can best be understood by exploring what exactly causes them. When the brain is violently moved, as it is in a concussion, it is often twisted which can damage both the brain cells and blood vessels that feed them, explained Dr. Kelly. Neurobiologist Dr. David Hovda added that the mechanical injury further disrupts the chemicals responsible for brain functions which in turn can produce an altered state of consciousness and can explain many of the symptoms associated with what athletes sometimes report as a “ding.”

The initial insult to the brain unleashes a biochemical cascade of effects that may not surface for days to weeks following a concussion and makes the brain particularly vulnerable to additional injury, animal and human studies reveal, said Drs. Kelly and Hovda.

Dr. Hovda’s studies on rodents revealed that a concussion causes their brains to be flooded with an excess of potassium and calcium ions, potent chemicals that can cause severe damage to cells when they appear in excess. The brain needs large amounts of the sugar, glucose, which is its primary energy source, to activate cellular pumps to counter this flooding of ions, Dr. Hovda said. Normally blood flow to the brain would supply it with this needed sugar, but the flood of calcium ions in the brain restricts blood flow by constricting blood vessels and also hampers the breakdown of glucose, a necessary step for the brain to convert glucose to useable energy. In addition, the blood vessels are constricted by mechanical pressure as the brain swells. Dr. Hovda described the end result as an energy crisis in the brain that can last for weeks following a concussion.

If another concussion occurs before the brain recovers from its first concussion, these energy starved brain cells are then more susceptible to dying. Hovda noted that this biochemically induced vulnerability of the brain is seen following both mild and severe brain injuries in people and is correlated with hampered brain functioning. “I don’t know what is so mild about mild traumatic brain injury,” he mused, referring to the more formal term for a concussion.

If another concussion occurs before the brain recovers from its first concussion, these energy starved brain cells are then more susceptible to dying.

If people are unfortunate enough to experience a second concussion before they have fully recovered from their first, they can experience a life-threatening swelling of the brain, no matter how minor the first or second bang to the head appeared to be, according to Dr. Kelly. This “second impact syndrome” (SIS) can cause major long-lasting brain damage and disability or even death. Avoiding this syndrome should be paramount in deciding when an athlete can safely play sports again, noted Dr. Kelly. (See Return to Play After a Concussion section below.)

Death ensues in half of all people with SIS, pointed out pediatrician and sports medicine expert Dr. Hergenroeder, and those that survive the condition are often left with significant brain damage, including impaired hearing or vision, extreme emotionality, and inability to concentrate or pay attention, which leads to poor school performance. SIS is rare, and reports in the literature suggest that it seems to mainly afflict male adolescents and young adults, noted Drs. Kelly and Hergenroeder.



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 7
Is Soccer Bad For Children's Heads?: Summary of the IOM Workshop on Neuropsychological Consequences of Head Impact in Youth Soccer CONCUSSION IS A BRAIN INJURY The spectrum of concussion signs and symptoms and their seriousness can best be understood by exploring what exactly causes them. When the brain is violently moved, as it is in a concussion, it is often twisted which can damage both the brain cells and blood vessels that feed them, explained Dr. Kelly. Neurobiologist Dr. David Hovda added that the mechanical injury further disrupts the chemicals responsible for brain functions which in turn can produce an altered state of consciousness and can explain many of the symptoms associated with what athletes sometimes report as a “ding.” The initial insult to the brain unleashes a biochemical cascade of effects that may not surface for days to weeks following a concussion and makes the brain particularly vulnerable to additional injury, animal and human studies reveal, said Drs. Kelly and Hovda. Dr. Hovda’s studies on rodents revealed that a concussion causes their brains to be flooded with an excess of potassium and calcium ions, potent chemicals that can cause severe damage to cells when they appear in excess. The brain needs large amounts of the sugar, glucose, which is its primary energy source, to activate cellular pumps to counter this flooding of ions, Dr. Hovda said. Normally blood flow to the brain would supply it with this needed sugar, but the flood of calcium ions in the brain restricts blood flow by constricting blood vessels and also hampers the breakdown of glucose, a necessary step for the brain to convert glucose to useable energy. In addition, the blood vessels are constricted by mechanical pressure as the brain swells. Dr. Hovda described the end result as an energy crisis in the brain that can last for weeks following a concussion. If another concussion occurs before the brain recovers from its first concussion, these energy starved brain cells are then more susceptible to dying. Hovda noted that this biochemically induced vulnerability of the brain is seen following both mild and severe brain injuries in people and is correlated with hampered brain functioning. “I don’t know what is so mild about mild traumatic brain injury,” he mused, referring to the more formal term for a concussion. If another concussion occurs before the brain recovers from its first concussion, these energy starved brain cells are then more susceptible to dying. If people are unfortunate enough to experience a second concussion before they have fully recovered from their first, they can experience a life-threatening swelling of the brain, no matter how minor the first or second bang to the head appeared to be, according to Dr. Kelly. This “second impact syndrome” (SIS) can cause major long-lasting brain damage and disability or even death. Avoiding this syndrome should be paramount in deciding when an athlete can safely play sports again, noted Dr. Kelly. (See Return to Play After a Concussion section below.) Death ensues in half of all people with SIS, pointed out pediatrician and sports medicine expert Dr. Hergenroeder, and those that survive the condition are often left with significant brain damage, including impaired hearing or vision, extreme emotionality, and inability to concentrate or pay attention, which leads to poor school performance. SIS is rare, and reports in the literature suggest that it seems to mainly afflict male adolescents and young adults, noted Drs. Kelly and Hergenroeder.

OCR for page 7
Is Soccer Bad For Children's Heads?: Summary of the IOM Workshop on Neuropsychological Consequences of Head Impact in Youth Soccer 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.