It's that eerie feeling you get where you could swear you've lived that very moment before, but of course logic tells you that just couldn't be possible.
Déjà Vu is a common intuitive feeling that has happened to many of us -- around 60 to 70 percent in fact. The expression is derived from the French, meaning "already seen". When it occurs, it seems to spark our memory of a place, person or act we have already experienced before.
Some believe that the feeling occurs when things from past lives merge into the present, though of course that theory is impossible to prove. Others think it is linked to recalling our dreams.
"Déjà vu, from a psychological perspective, is thought to be a caused by a memory mismatch which causes us to feel that we have already experienced an event when we know that the event is completely novel," Dr Amy Reichelt, Senior Research Associate at the UNSW told The Huffington Post Australia.
To first understand how déjà vu might have something to do with our memory, we need to understand how our memory works.
"The brain is thought to have two memory systems -- short term memory, which has a limited capacity and processes incoming sensory information from the environment. Information in short term memory gets forgotten rapidly unless transferred to long term memory stores. Our new experiences are processed by short-term memory and transferred into long-term memory."
"Our long term memory has what could be an infinite capacity for information. The long-term memory stores knowledge of episodes that shape our lives and can be recalled in detail. The critical brain region that stores our memories is the hippocampus - damage to this area leads to amnesia as new memories can’t be stored," Reichelt said.
Though not fully proven, Reichelt reveals that it is thought that déjà vu is down to a communication issue between short term and long term memory, sort of like a circuit break.
"So far there is no simple explanation as to why déjà vu occurs. It is thought that déjà vu could be evoked by a mismatch between the sensory input and memory-recalling output. This theory indicates that the mismatch between knowing an event is new, but it feeling familiar, is because of sensory environmental information is going straight into long term memory."
"The familiarity we experience in a déjà vu event exposes that there are different memory systems located in the hippocampus. Instead of sensory environmental information passing from short-term stores into long term memory, in déjà vu, information bypasses short term memory and instead reaches long term memory stores directly. This explains why a new experience can feel familiar, but not as tangible as a fully recalled memory," Reichelt said.
Or, it could be a glitch in the Matrix, right Neo?