Written by Deanna Tartaglia, this article was selected as a winner of our 2023 High School Science Communication Challenge. Tartaglia is a student at Newton North High School in Newton, MA. 

What is that sensation?

Our brains are extraordinary machines capable of storing and recalling countless memories. Yet, our brains aren’t infallible: they forget — and sometimes they remember things wrong. While it can be annoying to forget a friend’s birthday or a doctor’s appointment, it is much more disconcerting to remember something that never happened. Although this sensation may sound foreign, you have probably experienced it as déjà vu.

Above: Artist Pia Männikkö’s interpretation of the sensation of déjà vu. Courtesy of Pia Männikkö.

False Memories

Akira Robert O’Connor is a cognitive scientist at the University of St. Andrews whose

research suggests that the sensation of déjà vu is akin to your brain fixing a mistake. This theory is known as false memory: your brain is programmed to recognize familiar stimuli, but, in some cases, it can be falsely activated so that the feeling of recognition sets in with no actual memory to back it up. Your brain realizes that there is no memory matching the recognition, producing the strange feeling of déjà vu.

Despite its unsettling feeling, the fact that your brain can do this is a great sign. Patients with dementia are not as lucky: their brains trigger the recognition but are not able to correct it. This can lead to troubling behaviors like refusing to complete important tasks because they feel they have already done them. To test whether this corresponded to déjà vu, researchers studied the regions of the brain responsible for memory in people with dementia and without. They then compared these findings to the subjects' respective responses to false memory. The effects of neurological differences on the patients' experience with déjà vu helped researchers form a connection between memory and this phenomenon.

Not all scientists agree with O’Connor’s false memory theory. A new study using Magnetic Resonance Imagining (commonly known as MRI) to analyze participants’ brain activity suggests that indicated the hippocampus of our brains, an area responsible for memory, is not triggered during the sensation of déjà vu as proposed by O’Connor’s research. So, what else could be causing it?

‍Maybe It Really is Familiar

An alternative theory is that déjà vu is not a result of random activation of the recognition centers in our brains and is instead onset by familiarity. Studies conducted by Leeds Memory Group tested this theory by placing patients under hypnosis. The test subjects would form memories and then forget them under the influence of a hypnotist. When these stimuli were exposed after the hypnosis was broken, the same sensation as déjà vu was triggered. This study suggests that déjà vu occurs when we encounter something similar to a familiar situation and our brain notices the connection.

These contrasting theories of false memory or familiarity were brought together by neurologist Jean Khoury at the Cleveland Clinic Department. He proposed that the sensation was a miscommunication between the regions in the brain that control both memory and familiarity.

Whether you agree with the false memory or familiarity theory — or a combination thereof — this field of neurological research shows promising results in working to find the scientific basis for déjà vu. However, there is not yet a definitive answer as to why we feel this funny sensation. Perhaps someday soon these scientists will publish a breakthrough — we just hope it won’t feel like anything we’ve read before.