You are sitting in a new restaurant when all of a sudden you get the impression you have been there before and you know what is going to happen in the next few seconds… This strange feeling is what we commonly call “déjà vu”.
You are sitting in a new restaurant when all of a sudden you get the impression you have been there before and you know what is going to happen in the next few seconds… This strange feeling is what we commonly call “déjà vu”. However, a group of researchers from the Massachusetts Institute of Technology (MIT) in the United States think they have debunked the whole phenomenon, and can explain how it actually happens.
We know that when the brain is faced with a new situation, it files away details such as smells, sounds, colours, emotions, etc., creating a sort of mental “map” to be used in the future. When a new experience happens and the brain detects a detail that is strongly linked to a previous experience, it will associate the sensations from the first experience with the one currently happening. This gives us the impression that we are living through it a second time. Scientists say it is nothing more than a malfunction in our brain’s ability to sort through the new information, and is what they call an “episodic memory”.
The MIT researchers devised an experiment in which mice were put in a cage and then moved to a second cage that was identical to the first cage. The mice were then brought back to the first cage. In one of the cages, the mice received a mild electrical shock to the foot.
Two groups of mice were used in this study: mutant mice and healthy mice. The mice from the first group were genetically altered, lacking a specific gene crucial in sorting through similar experiences. This sorting process happens in a specific part of the hippocampus called the dentate gyrus. Therefore, because of the missing gene, the mutant mice were unable to make the difference between similar experiences. The second group was composed of healthy mice.
The researchers noticed that the mutant mice could not differentiate between the two cages. In fact, they were unable to discern in which cage they had received the electrical shock. To avoid being jolted again, they simply stopped moving the moment they were placed in either cage. However, the healthy mice were quickly able to tell the difference between the two cages, and only froze in the “dangerous” cage.
Brain activity from both groups of mice was measured. Researchers noted that the mutant mice had identical brain activity in both cages, while the healthy mice reacted differently in each cage.
According to the researchers, the behaviour of these mice confirms the role of this specific region of the brain (dentate gyrus) in the management of similar experiences. In addition, the analysis of brain activity allowed the scientists to establish the cellular and molecular pathways at work in this particular process.
Studies such as this one serve to help researchers increase their understanding and knowledge of brain function. Greater understanding could one day lead to better treatments and even curing certain neurodegenerative diseases like Alzheimer’s disease.