“Déjà vu”, “Dreams”; What’s the neurophysiologic basis?

The term ‘déjà vu’ is used in a common parlance

Dr.Vivek Nalgirkar

7/26/2021 0 min read

“Déjà vu”, “Dreams”; What’s the neurophysiologic basis?

Dr. Vivek Nalgirkar


The term ‘déjà vu’ is used in a common parlance. If we believe that a particular event has occurred exactly in a similar fashion in the past, we call it a sense of déjà vu. The term is often used metaphorically, if an event, by sheer happenstance or coincidence, repeats itself. Although this use of the term is a conscious expression to symbolize the repetitive events, in medical jargon its use is an expression of a subconscious mind. All of us get the feeling once in while, that a certain event has occurred in the past. We are talking to someone at a particular place, we get a subconscious feeling that the same talk has occurred in the same place with the same person in the past. So what’s the physiologic basis for this? The answer lies in the synaptic connections of our central nervous system. Short-term memory is based on the ‘post tetanic potentiation’ of some CNS (cortical) synapses. Then, the ‘working memory’ is formed in the cortex. This memory is then converted into long term memory in the (CA1 region of) hippocampus. Finally, the hippocampal projection to neocortex ‘consolidates’ the long term memory. In my opinion, some short-circuiting of this process may be responsible for the feeling of déjà vu. In the midst of an ongoing event, this process of memory formation/consolidation gets short-circuited, and the same event, even as it is occurring (for the first time) is bounced back from the cortex-hippocampus to make us believe or ‘feel’ that the exact same thing has occurred earlier. This short-circuiting is short-lived, though. The nascent synaptic connections either do not get consolidated or get erased or deleted. How else can one explain that our déjà vu events generally are never repeated for the second time?! I mean, we get this feeling only once for a particular event. If the event has really occurred in the past, and has got ‘consolidated’ in the memory, the feeling should have occurred repeatedly, at least every time that we are in the similar situation. 

The nascent synaptic connections are also responsible for our dreams. (I mean, the real sleep dreams; I am not talking of the ‘day dreams’ here.) Most of our dreams are meaningless, or so we believe. Yes, the entire dream may be meaningless, but if you rewind your dream carefully, you will note one thing. Although the entire sequence of events had no meaning or relevance, we can break it into parts and sub-parts. And, those subdivisions are meaningful; they are real. For instance, in a dream, you will see someone from your long gone distant past. And, in that dream, you might be talking something which has a relevance in your recent life. Now, seen in isolation, both the things (the person and the talk) are for real or meaningful. However, when combined together, it becomes meaningless. Try analyzing your dream next time and you will realize this. The parts of the dream are for real, but the dream on the whole is vague and unexplainable. 

This again can be explained on the basis of the ‘short-circuiting’ of some nascent synaptic connections. It is well known that the memory consolidation occurs during REM sleep. We have memories of events/persons/places stored in our synapses, in a patchy manner, in different regions of the cortex. When these neurons temporarily meet to form new synapses, these will be ‘nascent’ connections. The dendritic geometry is changing during this time. So, these patchy memories get lined up or circuited temporarily, to give you a sequence of events which has no real meaning, no real sense. These nascent dendro-dendritic connections are lost subsequently. How else can one explain that sometimes we are a part of a particular dream throughout the night, yet we can’t recall it in the morning? How else can one explain that we generally do not ‘remember’ or recall a dream the next or next-to-next day?


Dr. Vivek Nalgirkar