Origins of déja vu
Current neurobiological knowledge indicates that déja vu is a form of temporal lobe epilepsy, and it has also been associated with psychiatric disorders.
Déja vu has been suggested to possibly arise from a loss of synchronisation in between each cerebral hemisphere (half) of the brain: Each hemisphere contains a ‘self’, and one can view a scene from both selves simultaneously - thus fomenting déja vu. Admittedly, however, this explanation is rather abstract despite being rooted in neuropsychology.
Other psychiatrists suggest that essentially, déja vu is not necessarily a phenomenon in itself but a perceived phenomenon - i.e, people tend to believe they have seen the scene before but have really not. This can occur by extrapolating a small sight to an entire scene, or by associating an immediate event with something deep in the past. Such warped associations have consistently suggested a relation with psychiatric disorders.
Another explanation (the ‘tape recorder’ hypothesis by De Nayer) is that sights are somehow both perceived (seen) and recorded (transcribed into memory) at the same time, which is why one appears to recall an event immediately after seeing it. Again, however, the above explanations are largely theories, and their explanations are rather cognitive than neurobiological in themselves.
Overall, there have been around 50 postulations for déja vu. Their general ideas are summarized in this screenshot taken from Neppe’s paper (2010):
Anatomically, déja vu-like experiences have been associated with temporal lobedisorders. Moreover, electrical stimulation of deceased hippocampus(involved in memory) and amygdala (emotion) regions elicited a similar state.As such, the limbic system has shown to play a crucial role in inducing experiential phenomena such as déja vu.
Below is an image of the limbic system:
This idea of the hippocampus, amygdala and temporal lobe being activated are theorized to support the tape recorder hypothesis. It is suggested that the temporal lobe perceives and encodes information, storing it in the hippocampus. This information then gains meaning or emotion via the amygdala, which contributes to the familiarity of an event seen. Thus, the activation of memory and sensory structures simultaneously are proposed to create déja vu. This model has been supported by other researchers
However, this does not mean that all of déja vu boils down to three structures: these are merely the primary regions involved. It is proposed that entire ‘parallel’ neural networks are involved in encoding a specific experience.
Linked is a paper that neatly summarizes all prior and newer theories regarding déja vu - both psychological and anatomically. I would highly recommend to read it if interested: Understanding Déjà vu: Explanations, Mechanisms and the ‘normal’ kind of déjà vu