Concussions are a popular topic in the sports world these days. Especially hockey, of which I am a big fan. A player on my favorite team is currently not playing because of a concussion. Perhaps the number one star of the game, Sidney Crosby, is also suffering from a concussion. In fact, it seems as though every week, another player suffers a concussion. Apparently, about 300,000 concussions per year are due to sports or recreational activities. Except for common symptoms such as headache, dizziness, vomiting, nausea, loss of motor coordination, and cognitive deficits, we rarely if ever hear about what changes occur that are responsible for the symptoms. It seems as though little is known about the subsequent changes that occur in the brain that underlie the symptoms.
A research article was published last month that may give us a clue as to what damage may underlie the symptoms of traumatic brain injury that we call concussions. The brain is made up of billions of neurons, specialized cells that form a complex network that underlies the brains function. These neurons connect to each other via processes called axons. Often, these axons are covered by a myelin sheath, a fatty substance that is white in color. Areas that are predominantly made up of cell bodies are gray in color. Hence the terms white matter and gray matter when describing different parts of the cerebral cortex, the large outer shell of our brain. One theory, is that axonal injury underlies the long-term symptoms associated with concussions. Bazarian and his colleagues looked at nine high school athletes engaged in hockey or football and six who did not play contact sports. They used a technique called diffusion tensor imaging (DTI) to scan their brains during both pre-and postseason. DTI is a refinement of magnetic resonance imaging (MRI) that allows the doctor to measure the flow of water and track the pathways of white matter in the brain. Their hypothesis was that if an individual suffers axonal damage as a result of a concussion, then we should see changes in their white matter. They performed the DTI before the season started and after it ended.
They found that the one subject that suffered a concussion showed significant white matter changes, including in one pathway called the inferior longtitudinal fasciculus, which is involved in the semantics of language and verbal memory. The concussed subject’s performance on verbal memory tasks was relatively poor. They also found significant white matter changes among six atheletes with multiple subconcussive headblows (SHB). The proportion of white matter changes increased as a function of injury severity, from controls who suffered no head blows, to the athletes who suffered multiple SHBs, to the single concussed athelete. While this data is only correlational, that is it does not prove a causal relationship, it may be that the symptoms associated with concussions could be largely due to axonal injury — that is the disconnection between different brain areas.
Source: Bazarian, J. J., Zhu, T., Blyth, B., Borrino, A., & Zhong, J. (2012). Subject-specific changes in brain white matter on diffusion tensor imaging after sports-related concussion. Magnetic Resonance Imaging, 30(2), 171–180.
