If you’ve ever struggled to remember the name of a movie you watched just two nights ago, it may astound you to know that almost no one forgets how to ride a bike. Despite a rather steep learning curve at the outset and with plenty of skinned knees, it just doesn’t happen. So, why can’t we remember details from two days ago, but we remember how to do something we learned how to do in childhood? It turns out we have two different kinds of long-term memory: declarative and procedural. Within declarative memory are two sub-types: episodic and semantic memory. Episodic memory is the recall of an event in your life — like going to a concert or falling into a ditch. Semantic memory is factual, like knowing that John F. Kennedy was assassinated in 1963. Acquiring a skill — like riding a bike — is part of procedural memory that’s stored in another part of the brain. It's theoretically possible to suffer a brain injury that could rob you of your memory of riding a bike, while preserving the part that knows how to ride a bike. Why is procedural memory so stubborn? The regions in the brain where movement patterns are formed experience less nerve cell turnover, helping to preserve recall of those actions. That’s why you can hop on a bike and ride, but not necessarily remember the name of that movie you saw a couple of days ago. Alternatively, maybe the movie just wasn’t that good.
