Why do we sometimes mix details from different events together in memory?

Have you ever wondered why it can be so easy to get different events confused in memory? Maybe you go the movie with your friend Sarah and go to dinner with your friend Robert. Later, you think you saw the movie with Robert and had dinner with Sarah.

But why does this happen?

Just like a computer can have glitches, our memory systems sometimes make mistakes, too. These memory errors tell us a lot about how the brain works.

The type of memory error just described is a type of “associative memory error.” You know you did something with Sarah and Robert, but you get confused about which activity you did with each of them.

Associative memory relies heavily on the hippocampus, that seahorse-shaped region of the brain that we’ve talked a lot about before. It’s a hard type of memory task for the hippocampus, because it has to connect (associate) things together in a certain way (Robert with dinner, and Sarah with movie). It sometimes gets the connection wrong, because the brain doesn’t permanently store these connections. We have to rebuild them when we recall the memories! That’s hard work, and sometimes the brain doesn’t do it quite right.