"Deja vu" is the result of the interaction between perceptual system and memory system in human brain. To understand why there is a sense of "deja vu," scientists have to start with a classification of perception and memory. The process of classification is not only a basic feature of perception, but also a basic feature of memory. Perception includes face perception, object perception, position perception and so on. Take these three categories as an example. Because of their different objects, when we get to a place, the orientation and spatial relationship, the surrounding objects and people may appear at the same time. However, our perception of them is completed by three different empty energy circuits in the brain, namely, the circuit of position perception, the circuit of object perception and the circuit of face perception. Like perception, memory has many types.
The memory of knowledge and feeling is called semantic memory: the memory of plot, experience and events, that is, episodic memory, which is unconscious memory. Each kind of memory can be divided into many subclasses. Because perception and memory are classified, many features of some scenes we have experienced are stored in different memory systems, and we can't realize that when we come to a new scene, some parts of the scene may stimulate our memory, mobilize different memory systems and match with them. Once a certain feature in the scene matches the past experience, it will produce the feeling of "deja vu". Everyone has a life experience, because there are so many things to accumulate. It's very normal to have the subjective experience of "deja vu" occasionally. The initial understanding of the subjective experience of "deja vu" can be traced back to epilepsy in medicine. Half a century ago, normal people also had this subjective experience. With the accumulation of brain science knowledge, it gradually reached today's level of understanding.
It often happens when the mood is unstable
It's not easy to realize 'deja vu'. "Deja vu" is easy to occur in the emotional instability and the experience of the scene. Although all people will have the subjective experience of "deja vu", it does not mean that the frequency of "deja vu" in all people is the same. Generally speaking, things closely related to emotions are easier to remember than those closely related to emotions. Therefore, if you are in a state of emotional instability, then the probability of "deja vu" is to blame. During puberty, people's mood and memory will be in a very unstable state during menopause. At this time, it's more likely than some to have a 'deja vu' situation. "Deja vu" mainly occurs in the experience of the scene. It is because every perception appears in a specific scene. This kind of scene is often a big background, without special attention, it will run to the brain to form unconscious memory. This kind of unconscious memory sometimes pops up in a specific scene and mixes with perception. In the case of 'deja vu', most of them are unconscious memories. From childhood, all the experiences, whether they want to remember or not, have traces of these memories in their minds, and they pop up in some very special circumstances. When it comes to consciousness, it creates a sense of "deja vu.".