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Déjà vu – Have We Been Here before?
Written by Kiran Nayager
Edited by Harry Yang
You speed-walk into the lecture theatre, slightly out of breath with your morning coffee in hand, trudging down the stairs as students whip their heads around to see if their late-coming friend has arrived. The lecturer conquers their battle with two-factor authentication and finally projects their presentation when you flip the thin seat down and hear your friend complaining about the day ahead. Your face is half buried in your bag, searching for your iPad, when you suddenly look up and feel like this has happened before. Not a situation like this, but a situation exactly like this.
Every detail is eerily the same – the powerpoint slides on cerebral blood supply, the words your friend is muttering, the breeze of the overhead air conditioner. But then, all the similarities disappear as you are grounded back in reality. You’ve never had a lecture on cerebral blood supply, the air conditioner barely works in the lecture theatre, come to think of it, this is the first lecture you’ve attended in months!
The feeling of déjà vu is a common experience, often fleeting, but uncanny nonetheless. The term is borrowed from French, meaning ‘already seen’, and is formally defined as the representation of:
“the clash between two simultaneous and opposing mental evaluations: an objective assessment of unfamiliarity juxtaposed with a subjective evaluation of familiarity.” (Brown 2004)
While some like to attribute the sensation as illuminations of their past life, neuropsychiatric studies suggest instead abnormal neural memory pathways.
For example, one popular theory is that déjà vu is an erroneous recognition, induced by a mismatch in recollection and familiarity processes. Recollection is distinguished from familiarity as a deliberate and conscious remembering of experiences, while the latter is a much faster, and ambiguous process, which underpins recognition. Thus, to understand why déjà vu occurs, we first must understand the neural pathways involved in recollection of events.
Recollection is associated with hippocampal and posterior parahippocampal neural activity, whereby the parahippocampal cortex is thought to enhance recollection by accessing contextual information. Comparatively, familiarity is associated with perirhinal cortex activity, which retrieves specific information about items. Recognition of an event or object is finally formed as a summation of these circuits, combined with cortico-hippocampal and prefrontal cortex inputs, which selects context-appropriate memory representations.
Hence, many hypotheses posit that déjà vu may involve inappropriate parahippocampal activity in the memory response, when coordinating and synthesising information regarding recollection, familiarity and recognition. Interestingly, increased frequency of déjà vu experiences are correlated with epileptic seizures, which has consequently grounded much of the natural research and experimentation.
Intracranial stimulation studies have found that there is no déjà vu centre, but it is rather caused by erroneous signals within the medial temporal network. Electrical stimulation to parts of the medial temporal lobe activates parahippocampal, hippocampal and entorhinal regions, which work together to produce déjà vu in patients. Furthermore, while déjà vu is associated with focal aware seizures specifically, déjà vu is not a sign of seizure. Excessive excitation within the medial temporal lobe, such as in seizures, is also associated with increased reminiscence, thus bringing into question the difference between déjà vu and reminiscence.
Neuropsychologists distinguish reminiscence as a retrieval of stored memory, without erroneous familiarity. Reminiscence also causes activation of the perirhinal cortex (rather than entorhinal), which integrates information alongside the hippocampus and broader memory networks. While the memories contributing to déjà vu are classed as episodic memories, centering around events, reminiscence is more strongly linked with semantic memories, which are associated with words.
Another psychological experience akin to déjà vu is the ‘tip of the tongue’ phenomenon – the slight embarrassment and pondering confusion as you pause mid-sentence, trying to search for a word, knowing it is there, but to no avail. Researchers attribute this phenomenon to activation of recognition pathways, but not the actual memory pathway to access the material.
Thus, while déjà vu, and even other similar processes, is a complex conflict between recognition, familiarity and recollection, its transience is what makes the experience so captivating. It rapidly suspends your multisensory perspective of the world for a fleeting moment, as you dissociate into the inner cortices of your brain, searching for the memory of what you’re currently experiencing. Your search ends, almost as abruptly as it began, and you return to the lecture theater. Your friend continues complaining, the lecturer starts reading the learning objectives and you open your iPad to the slides.
Still, as you continue to watch the lecture, half your attention is trying to figure out:
“Have we been here before?”
References
Aitken, C. B. A., Jentzsch, I., & O’Connor, A. R. (2023). Towards a conflict account of déjà vu: The role of memory errors and memory expectation conflict in the experience of déjà vu. Neuroscience & Biobehavioral Reviews, 155, 105467. https://doi.org/10.1016/j.neubiorev.2023.105467
Brown, A. S. (2004). The déjà vu experience. Psychology Press.
Hadzic, A., & Andersson, S. (2024). Non-ictal, interictal and ictal déjà vu: A systematic review and meta-analysis. Frontiers in Neurology, 15. https://doi.org/10.3389/fneur.2024.1406889
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