What causes déjà vu and why does our brain experience it?

You get déjà vu when your brain thinks it’s seen something before, even though it really isn’t, like when you walk into a room and suddenly feel like you’ve been there a million times.

Your brain has two main parts that work together to help you understand what's going on around you. One part is fast, like a detective who runs in and catches the culprit right away, this is your short-term memory. The other part is slower, like a detective who takes notes and checks everything carefully, this is your long-term memory.

Sometimes, when something happens quickly, the fast detective gets confused and thinks it's seen that thing before, even though the slow detective hasn’t had time to check yet. That’s why you feel like you’ve been somewhere or done something before, even if you haven’t!

Imagine you're eating your favorite sandwich, say, a peanut butter and jelly one. You bite into it, and suddenly you think you've eaten this exact same sandwich before. It's not magic, your brain just got mixed up for a moment!