The devastating and life-altering medical consequences of getting knocked out cold are far from what the movies have made them out to be. Dr. Marian Berryhill of the University of Nevada, Reno Department of Psychology explains the effects of repeated blows to the head as they are observed in professional athletes:

“The brain basically crashes into the skull,” says Dr. Berryhill, “And then it bounces back and crashes against the other side of the skull — then you get abrasions and bruising on the brain. Now [sometimes] there’s a twisting — when there’s torsional movement — [and this is often the case] with hockey players. You have the cortex that’s kind of loosey-goosey, and the brain stem which is a little denser — and they can twist against each other.” This type of injury is often fatal.

“And if you’re repeatedly crashing the front of your head into things,” Dr. Berryhill continues, “You’re pretty much guaranteed to damage your frontal lobe. I don’t want to overstate the situation, but athletes who have experienced tremendous numbers of concussions — there is tremendous evidence that they’re not doing very well.

Higher rates of dementia, chronic anger, depression, sleep disturbances, assaults and arrests are all traits associated with Chronic Traumatic Encephalopathy (CTE). This condition is caused by concussions and repeated blows to the head. Researchers discovered CTE damage in post-mortem studies of the brains of former athletes and murderers, Chris Benoit and Aaron Hernandez.

“You’re not messing around with, y’know, your pinky toe,” says Dr. Berryhill. “We’re talking about the core of who you are. And the consequences can be grave.”