donderdag 3 maart 2016

The danger of concussions

It is becoming increasingly clear that concussions have long term effects - and not only for boxers. The Economist (Bang to rights: Science is taking big steps toward understanding the impact of concussion) gives an overview. In recent years the underlying biology has started to become apparent. Mostly, this relates to the release of certain chemicals when axons, the filamentous connections between nerve cells, are damaged. Concussion is different from blunt-force trauma, such as that which results from getting hit on the head by a rapidly delivered cricket ball. Then, the injury is caused by directly transmitted shock from the impact. Concussion, by contrast, is caused by the internal movement and distortion of the brain as it bounces around inside the cranium after an impact. This bouncing, research has shown, stretches and deforms bundles of axons that connect different regions of the brain. The deformation shears some axons directly, releasing their protein contents, including tau, which with time can form abnormal tangles similar to those found in Alzheimer’s disease. It also causes abnormal inflows of sodium and calcium ions in unsevered but damaged axons. These, in turn, trigger a process which releases protein-breaking enzymes that destroy the axon, further disrupting the brain’s internal communications. Concussive injury also damages the blood-brain barrier. This is a system of tightly joined cells surrounding the capillaries that service the brain. Its purpose is to control what enters and leaves the central nervous system. One consequence of damaging it is to release into general circulation a brain protein called S100B. The body mounts an immune response against this protein, and the antibodies it generates can find their way back into the brain and harm healthy brain cells. Researchers propose that repeated damage could set the stage for a continuous autoimmune-type attack on the brain. But the long term effects are still unclear. There are efforts to develop a blood test with which you could measure the seriousness of a concussion - by measuring one of chemicals involved. Finally the harm caused by concussions with children is discussed: Yet it has been clear since a study published in 2012 by Andrew Mayer at the University of New Mexico in Albuquerque that subtle brain changes in children who have sustained a concussion persist for months after the injury, even when there are no longer any obvious symptoms. Work published last December by Charles Hillman of the University of Illinois found that children who had sustained a single sports-related concussion still had impaired brain function two years later. Ten-year-olds with a history of concussion performed worse on tests of working memory, attention and impulse control than did uninjured confrères. Among the children with a history of concussion, those who were injured earlier in life had larger deficits. This study was small (it involved 15 injured participants) but if subsequent research confirms it, that will be great cause for concern.

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