During the NHL playoffs this year, a player named Niklas Kronwall plastered a player named Martin Havlat, as seen in this video:

In the process it is likely that Havlat got a concussion, either from the hit itself, or the fall, or both. Havlat was unconscious on the ice for about a minute.

So what is happening during a concussion? In essence, a concussion (aka a traumatic brain injury) is a brain injury where the axons connecting neurons of the brain together are torn. In a mild concussion, a relatively small number of axons are damaged. In more severe concussions, a large number are damaged. This video shows very nicely how the damage happens:

Medical Animation: TBI – Traumatic Brain Injury

Obviously if you rip out some of the wiring of the brain, there are going to be changes. A concussion affects things like memory, mood and even personality. In severe cases, a person with a TBI loses important functionality – for example the ability to walk, talk or read.

This video talks about the long-term effects of a traumatic brain injury. Sometimes it takes years for healing to occur:

In sports, there is now a lot of evidence to suggest that a person who has a concussion on top of a concussion is going to have a lot of problems. Therefore, when Havlat was back on the ice just two days later, it raised some eyebrows:

Havlat’s early return ‘shocking’: concussion specialist

See also this video on high school football head injuries:

See also: Is there a link between concussions and dementia?