Amnesia. It's a pretty way to add some drama to a story. A bowling ball to the head and, suddenly, Fred Flintstone can't remember who he is. Another bonk, and everything goes back to normal. It makes for some pleasant cartoon hijinks, but in reality, concussion-induced amnesia is a real thing and is really serious.

So, how does it happen?

The most common causes of amnesia are strokes, brain surgery, and infection in your brain. But amnesia can be caused by a concussion -when a bump to your head or body rattles your brain around in your skull, damaging delicate tissue. Sometimes that damage just makes you sleepy and head-achy for a few days, but the effects can be more serious. 

Right after you take a hit, those sloshed-around neurons in your brain are really fragile, which could lead to post-traumatic amnesia. See, damage to some parts of the brain can sometimes cause problems in connected regions, which is called diaschisis. And diaschisis has been linked to an imbalance in brain chemistry -specifically, in the neurotransmitter acetylcholine, which helps regulate signaling in the brain, and plays an important role in attention and motivation. 

So it could be that damaged neurons can't talk to each other normally, which makes things hard on the memory system. But researchers aren't exactly sure how these biological problems can lead to amnesia. Especially because there are two kinds of amnesia: retrograde and anterograde. And, of course, just to make things more complicated both can be caused by concussions. 

Retrograde amnesia is where you forget things that happened in your past -like how Jason Bourne can't remember who he is or where he came from in the Bourne Identity movies. It's pretty common for a concussion patient to forget what happened before the injury, including what caused it. In really severe cases, patients can forget days, week, or even years. As some of the brain tissue heals, some of those moments can start to come back. But they might never remember the moments just before their injury.

Anterograde amnesia, on the other hand, is where you can't make new memories -like how Dory forgets things in Finding Nemo. Some patients can even have trouble paying attention after a concussion, which might have tot do with that acetylcholine imbalance. 

Doctors can use all of these symptoms to help determine the severity of a head injury, and track a patients recovery. So more research on how concussion affects our brains will hopefully lead to better treatments. That way, patients can get back on their feet, and back to their memories, a little more quickly. 

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