Why do we experience déjà vu, and what causes it?

We experience déjà vu when our brain thinks it’s seeing something new, but actually feels like it has seen it before, kind of like when you hear a song and think you’ve heard it somewhere, even though you haven’t.

Your brain has two parts that work together to help you understand what you see. One part is fast and tells you what you're seeing, and the other takes a little longer and checks if you've seen something like this before.

Sometimes, the faster part sends the message first, "Hey, I think I know what this is!", but then the slower part catches up later with, "Wait, I’ve seen this somewhere before!" That’s when déjà vu happens, it feels like you're remembering something that just happened, even though it's brand new.

Imagine you’re walking into a room and see your favorite toy. Your brain says, “Oh, that’s my toy!” But then a second later, you think, “Wait… I’ve seen this before! Did I come here already?” That’s déjà vu, it's like your brain is playing a little trick on you, just like when you try to remember something and your brain gives you a surprise.