Why do humans experience deja vu, and what causes it?

Humans experience déjà vu when their brain thinks it’s seeing something new, but it actually feels familiar, like a memory from before.

Imagine you're playing with your favorite toy, and suddenly it looks just like the one you saw in a dream last night, even though you didn’t know that toy existed! Your brain is confused because it thinks it already knows this toy, but it's seeing it for the first time. That’s déjà vu.

Your brain has two parts working at once: one that takes in what you're seeing (like your eyes looking at a familiar street), and another that checks if it feels like a memory (like remembering walking on that same street before). Sometimes, the memory part gets ahead of the seeing part. It says, “I know this!” before the rest of the brain catches up, and that’s why you feel like you’ve been here before.

It's like when you hear a song you love, and it feels like you've heard it a million times, even though you're hearing it for the first time today. Your brain just got confused, but in a fun way!