A Glitch in the Mental Matrix: Exploring the Illusion of Déjà Vu

Dominic Matos and Tamar Paserman

Illustrations by Ming Na

It’s Thursday night. You and your boyfriend are celebrating your one-year anniversary at a classy local Italian restaurant. “That’s Amore” by Dean Martin plays in the background, and a dim, amber light sets the tone. You both browse the wine selection, and end up settling on the rosé. At the same moment, a group of waiters erupt into “Happy Birthday” at a nearby table. Suddenly, a strange sensation comes over you. This night doesn’t seem new anymore. Startled by the tune of “Happy Birthday,” you’re strangely filled with an eerie sense of déjà vu. The lights, the  music, the smells… everything feels familiar. “Have we been to this restaurant before?” you ask your boyfriend. “No, it just opened,” he replies. But you swear you’ve seen this before! A moment later, the feeling disappears, just as abruptly as it came. What is going on?  

Déjà vu — or ‘already seen’ in French — refers to the feeling that the current moment has already happened before. It is a strange, nearly universal occurrence, and while centuries of study have yet to fully clarify the neurological underpinnings of déjà vu, it is known that déjà vu-like symptoms can occur in certain forms of epilepsy [1, 2]. This finding, which connects a known biological condition to the ambiguous déjà vu, can provide a glimpse into how the illusion really works. In evaluating déjà vu through the lenses of memory, cognition, and neuroanatomy, we can arrive at a better understanding of its complex nature.

A Walk Down Memory Lane

To understand déjà vu, we must first understand how our memories are processed and retrieved. Our long-term memory is divided into implicit and explicit memory. Implicit memory is information that does not require active recollection — it is information you just know, like riding a bike or how to navigate through your home. These kinds of memories are typically learned through repetition and are effortlessly recalled by your unconscious mind [3]. Explicit memory, on the other hand, refers to the conscious recollection of facts or events. A category of explicit memory is episodic memory, which consists of specific lived experiences, such as your tenth birthday party or where you left your keys. Though there are different categories of memory, all memory processing and recollection involves the encoding, storage, and retrieval of memories [4]. Encoding is the process of acquiring information and incorporating it into memory, storage is the retention of memories, and retrieval is the bringing-to-mind of a previously stored memory [4].

Actively retrieving previously encoded information from your memory storage and reliving the event in your head is known as recollection, and can be thought of as mental time travel. Recalled information includes details and fragments from events, like the color of your childhood bedroom [5]. Familiarity is the related, but distinct, process of recognizing certain stimuli through learned association, such as when you see someone you know and automatically smile. Familiarity is subconscious, felt on a spectrum, and is experienced more quickly than recollection, which is an all-or-nothing phenomenon [5]. Recollection and familiarity are crucial components of explicit memory, since déjà vu occurs when the brain confuses familiarity for recollection [5, 6, 7].  It is also possible for feelings of familiarity to occur without an identifiable source, both in real memories and in déjà vu. For example, when you see a person you know but cannot recall why or how you met them, this could just be ‘poor’ memory, or a case of déjà vu [5]. However, feelings of familiarity can be so strong that a person can believe they are recollecting memories of something they never experienced; this is the eerie feeling you get when déjà vu hits. 

Déjà vu may be triggered when an appropriate sense of familiarity about one specific element of a situation is misattributed and extended to the entire scene [8]. Say you’ve spent the weekend researching Van Gogh paintings. The next week you walk into a museum and one of his paintings that you saw online is hanging on the wall. You don’t even notice the painting consciously, but your subconscious is familiar with it. Your brain mistakes the familiarity you feel for the recollection of an actual memory, and causes a sudden sense of déjà vu. With sirens of familiarity going off in your brain, you now feel as though you’ve experienced this place before, when in reality, you’ve only experienced the painting. A critical part of a déjà vu experience is knowing that this feeling of familiarity is wrong; you have not experienced the event before, despite the sense of familiarity [9]. Another possible trigger of déjà vu is the configuration of a setting. For example, if your cousin’s living room is arranged very similarly to yours, it could more easily trigger déjà vu than other places. [6]. The more scenes one witnesses — via traveling, dreaming, and watching movies — the greater the likelihood of experiencing déjà vu [6]. 

Nightmares Come to Life

Déjà vu is a complicated phenomenon to study, and while it is hard to pinpoint which parts of the brain are involved, the temporal lobe seems to be the best place to start. The temporal lobe, located in the brain behind our ears, is central to many cognitive functions and, most pertinently, regulates and controls memory storage [10]. Examining individuals with typical versus atypical temporal lobes may elucidate what happens in the brain when we experience déjà vu. For most people —and as in the Van Gogh example — déjà vu simply refers to an unexplained feeling of ‘I have already seen this before,’ which is known as non-pathological déjà vu. For others, however, déjà vu can occur as a symptom of an underlying disease or neurological abnormality [8]. This kind of déjà vu is defined as pathological [8].

The most common type of pathological déjà vu occurs in those with temporal lobe epilepsy (TLE), which is usually caused by damage to the temporal lobe [1]. TLE is the most common form of epilepsy, a neurological condition characterized by recurring, unprovoked episodes called seizures — sudden, uncontrollable surges of excessive electrical activity in the brain [2]. TLE is typically characterized by impaired long- and short-term memory as well as compromised executive function [2]. When you think of a seizure, you might picture a person experiencing sudden bursts of movement. In reality, this type of seizure is much less common than a typical seizure, which can look more like a person zoning out for a moment [11]. 

Since individuals with TLE can experience both pathological and nonpathological déjà vu, the neurological bases of déjà vu are commonly investigated through these populations [8]. TLE symptoms manifest in a variety of forms, but the more experiential or hallucinatory symptoms — such as sudden disorientation or intense, spontaneous disconnects from reality  — can be referred to as the ‘dreamy state.’ [12, 13] The ‘dreamy state’ is usually accompanied by feelings of déjà vu and strong negative emotions such as anxiety, fear, or general strangeness; one report from a person with TLE describes a vision of a “bald man dressed in black, coming towards her from behind, associated with a feeling of imminent death.” This hallucinatory state encompasses a clustering of various symptoms that may distort one’s consciousness [9]. The experience is associated with temporal lobe seizures and can be elicited by electrical stimulation of sections of the temporal lobe, like the amygdala and hippocampus — brain regions involved in memory processing [14]. 

People with TLE are more likely to report their déjà vu experiences, which can be intense, visceral, and out of the ordinary, with a wide range of possible presentations spanning from a simple sense of familiarity to an immersive state full of overwhelming emotions [15, 16]. During ‘dreamy states’ simulated via electrical stimulation, people with TLE have recounted experiences like reliving the past while still being conscious and able to “see [the present] clearly … as if what is happening now has already happened … like an old memory that I am in the middle of living out” [17]. Reliving a memory while also being conscious of the present is a central and curious aspect of the dreamy state [15]. People also often describe the dreamy state as being similar to dreaming even though they are awake and alert. Some memories experienced during the dreamy state are perceived in the third person as a spectator: one patient describes seeing themself “playing the drums, with people from [their] family listening” [15] when in this state. Individuals also often report experiencing déjà vécu in the dreamy state, an experience similar to déjà vu but can last much longer [17]. Déjà vécu can be described as a feeling that one has already lived through entire sequences of events, though these sequences do not start and stop as abruptly as déjà vu. When we experience déjà vu, typically our brain quickly dismisses the feeling as an error, but in cases of déjà vécu, the feeling persists, and the line between illusion and reality starts to blur [17]. For example, an individual with déjà vécu and seizures in the temporal lobe was convinced that TV shows and even live broadcasts of football matches were replays [17]. 

Mapping the Mental Matrix

Despite similarities in déjà vu experiences between individuals with and without epilepsy, there are structural differences in the brains of the two populations [9,18,19]. People with TLE who experience pathological déjà vu demonstrate contrasting temporal lobe structures to those without TLE who experience déjà vu [9, 18, 19]. Structural differences in brain tissues are specifically observed in grey matter, the tissue that contains the cell bodies of neurons. Grey matter is crucial for memory processing and the retrieval of episodic memories [18, 20]. Memory processing can be impaired when less grey matter is found in the limbic system, which is a series of interconnected brain regions in the temporal lobe that are involved in the regulation of emotional responses [21, 22, 23]. Emotion plays a large role in the recollection of memories, and since many episodic memories have an emotional aspect to them, the limbic system is strongly associated with the recall of memory and experience of the dreamy state during déjà vu [24, 23]. The structural differences in the brains of TLE patients reveal that TLE-induced déjà vu is fundamentally different from the déjà vu most people experience [21, 22, 23]. 

The differences between pathological and non-pathological déjà vu are also evident in case studies of individuals who experience both déjà vu forms. In one case of an individual with TLE, déjà vu was experienced both during a seizure and in the absence of a seizure [13]. The person felt a difference between the two kinds of déjà vu; when experienced in tandem with a seizure, it was associated with fear, dysphoria, and worry, whereas non-pathological déjà vu elicited more neutral feelings. In another study, a man with TLE tried to minimize his sense of déjà vu by diverting attention away from his déjà vu trigger, but the feeling of familiarity persisted regardless [25]. TLE déjà vu may be caused by more than just a person’s environment and familiarity; however, additional research is necessary [25]. These case studies utilizing self-report measures provide a lens into an individual’s experience, but they may not be generalizable to the broader population. 

Conclusion

Déjà vu inexplicably breaks the rules of our cognitive worlds. It bends what is ‘allowed’ in our memory and what is not. We feel familiarity from a situation we’ve never experienced, and we see the past in the present. Based on the current state of research, the temporal lobe, déjà vu, and dreamy state are interrelated. From errors in memory to differences in temporal lobe structures, there are many different explanations for the universally perplexing cognitive illusion of déjà vu. While the ‘dreamy state’ is specific to TLE, its similarities to déjà vu are strong enough to provide insight into the broader phenomenon. Since the neurological mechanisms of déjà vu have revealed its connection to TLE, we have begun to untangle the complexities and bridges between memory, cognition, consciousness involved in déjà vu. While déjà vu is a fleeting experience and you may not even remember the last time you had it, the sensation is all-consuming in the moment. At its core, déjà vu perfectly symbolizes the brilliant mystery that is the human mind. It’s a real-life glitch in your matrix. 

References

1. Engel, J. (2001). Mesial temporal lobe epilepsy: what have we learned? Neuroscientist, 7(4), 340-352. doi:10.1177/107385840100700410.

2. Stafstrom, C. E., & Carmant, L. (2015). Seizures and epilepsy: an overview for neuroscientists. Cold Spring Harbor Perspectives in Medicine, 5(6). doi:10.1101/cshperspect.a022426.

3. Hine, K., & Tsushima, Y. (2018). Not explicit but implicit memory is influenced by individual perception style. PLoS One, 13(1), doi:10.1371/journal.pone.0191654.

4. Brown, S., & Craik, F. (2000). Encoding and Retrieval of Information. In Craik, F. The Oxford Handbook of Memory, pp. 93-107. Oxford University Press. 

5. Yonelinas, A. P. (2002). The nature of recollection and familiarity: a review of 30 years of research. Journal of Memory and Language, 46(3), 441-517. doi:10.1006/jmla.2002.2864.

6. Cleary, A. M. (2008). Recognition, memory, familiarity, and déjà vù experiences. Current Directions in Psychological Science, 17(5), 353-357. doi:10.1111/j.1467-8721.2008.00605.x.

7. Squire, L. R., Wixted, J. T., & Clark, R. E. (2007). Recognition memory and the medial temporal lobe: a new perspective. Nature reviews. Neuroscience, 8(11), 872–883. doi:10.1038/nrn2154.

8. Wild, E. (2005). déjà vù in neurology. Journal of Neurology, 252, 1–7. doi:10.1007/s00415-005-0677-3.

9. Illman, N. A., Butler, C. R., Souchay, C., & Moulin, C. J. (2012). déjà experiences in temporal lobe epilepsy. Epilepsy research and treatment, 2012, 539567. doi:10.1155/2012/539567.

10. Patel, A., Biso, G. M. N. R., & Fowler, J. B. (2022). Neuroanatomy, Temporal Lobe. In StatPearls. StatPearls Publishing. PMID:30137797.

11. Kodankandath, T. V., Theodore, D., & Samanta, D. (2022). Generalized tonic-clonic seizure. In StatPearls. StatPearls Publishing. PMID:32119383.

12. Petitmengin P., Baulac, M., & Navarro, V. (2006). Seizure anticipation: are neurophenomenological approaches able to detect preictal symptoms?. Epilepsy & Behavior, 9(2), 298-306. doi:10.1016/j.yebeh.2006.05.013.

13. Cleary, A. M., Neisser, J., McMahan, T., Parsons, T. D., Alwaki, A., Okada, N., Vosoughi, A., Kheder, A., Drane, D. L., & Pedersen, N. P. (2021). Subjective distinguishability of seizure and non-seizure déjà vu: a case report, brief literature review, and research prospects. Epilepsy & behavior: E&B, 125, 108373. doi:10.1016/j.yebeh.2021.108373.

14. Bancaud, J., Brunet-Bourgin, F., Chauvel, P., & Halgren, E. (1994). Anatomical origin of déjà vù and vivid “memories” in human temporal lobe epilepsy. Brain, 117(1), 71–90. doi:10.1093/brain/117.1.71. 

15. Vignal, J., Maillard, L., McGonigal, A., & Chauvel, P. (2007). The dreamy state: hallucinations of autobiographic memory evoked by temporal lobe stimulations and seizures. Brain, 130(1), 88–99. doi:10.1093/brain/awl329.

16. Gillinder, L., Liegeois-Chauvel, C., & Chauvel P. (2022). What déjà vù and the “dreamy state” tell us about episodic memory networks. Clinical Neurophysiology, 136, 173-181. doi:10.1016/j.clinph.2022.01.126.

17. ​​Ter Meulen, B., Van der Meer, M., Hemmes, R. & Blom, J. D. (2021). déjà Vécu: When Groundhog Day Gets Real. Archives of Clinical and Medical Case Reports, 5. doi: 10.26502/acmcr.96550335.

18.  Labate, A., Cerasa, A., Mumoli, L., Ferlazzo, E., Aguglia, U., Quattrone, A., & Gambardella, A. (2015). Neuro-anatomical differences among epileptic and non-epileptic déjà-vu. Cortex, 64, 1-7. doi:10.1016/j.cortex.2014.09.020.

19. Brázdil, M., Mareček, R., Urbánek, T., Kašpárek, T., Mikl, M., Rektor, I., & Zeman, A. (2021). Unveiling the mystery of déjà vù: the structural anatomy of déjà vù. Cortex, 48(9), 1240-1243, doi:10.1016/j.cortex.2012.03.004. 

20. Irish, M., Hornberger, M., El Wahsh, S., Lam, B. Y., Lah, S., Miller, L., Hsieh, S., Hodges, J. R., & Piguet, O. (2014). Grey and white matter correlates of recent and remote autobiographical memory retrieval - insights from the dementias. PLoS One, 9(11). doi:10.1371/journal.pone.0113081.

21. Li, X., Wang, H., Tian, Y., Zhou, S., Li, X., Wang, K., & Yu, Y. (2016). Impaired white matter connections of the limbic system networks associated with impaired emotional memory in Alzheimer's disease. Frontiers in Aging Neuroscience, 8, 250. doi:10.3389/fnagi.2016.00250.

22. Maguire, E. A., Woollett, K., & Spiers, H. J. (2006). London taxi drivers and bus drivers: a structural MRI and neuropsychological analysis. Hippocampus, 16(12), 1091–1101. doi:10.1002/hipo.20233.

23. Rolls E. T. (2019). The cingulate cortex and limbic systems for emotion, action, and memory. Brain Structure & Function, 224(9), 3001–3018. doi:10.1007/s00429-019-01945-2.

24. Zarrindast, M. R., & Khakpai, F. (2020). State-dependent memory and its modulation by different brain areas and neurotransmitters. EXCLI Journal, 19, 1081–1099. doi:10.17179/excli2020-2612.

25. O’Connor, A. R., & Moulin, C. J. A. (2008). The persistence of erroneous familiarity in an epileptic male: challenging perceptual theories of déjà vù activation. Brain and Cognition, 68(2), 144-147, doi:10.1016/j.bandc.2008.03.007.