How many times has it happened to you that you are talking to someone and suddenly experience an overwhelming feeling of familiarity, as if this exact conversation already happened. Except, it hasn’t. This phenomenon is referred to as ‘déjà vu’. It is a fairly common feeling that most of us experienced at least once in their life. But why and how does it occur? Let’s find out!

This article will cover:

·       What is déjà vu?

·       Why does it occur?

What is déjà vu?

Déjà vu is a French term meaning ‘already seen’ [5] and it refers to a feeling of having experienced a situation before, despite knowing that you have not [1]. This phenomenon is quite common. Researchers estimate that between 60 to 80 per cent of the general population experiences it at least once in their life [6]. Experiences of déjà vu tend to peak in young adulthood and gradually decrease with age [5]. The reason why young people tend to experience it more often is related to periods of stress and exhaustion which are more prevalent in this population. These factors can in turn affect memory processes which are according to some scholars responsible for déjà vu [5]. Déjà vu has also been linked to feelings of premonition, meaning that during déjà vu, the person believes that they are able to predict what is going to happen next [2].

Link to temporal lobe and temporal lobe epilepsy

Déjà vu is regularly experienced by healthy people and is not usually a cause for concern [5].  However, déjà vu has been linked to temporal lobe epilepsy, a disruption in nerve cell activity which causes seizures [7]. People suffering from epilepsy report experiencing déjà vu right before a seizure, as a sort of ‘warning sign’ [3].

This suggests that déjà vu might be linked to memory, though a clear connection has not been fully established. For example, it appears to be linked to the hippocampus which is primarily responsible for memory storage and is located in the temporal lobe (lower lateral part) of the brain [7]. Other areas of the temporal lobe are also responsible for detection of familiarity and recognition of events or objects.

Why does it occur?

Despite the fact that déjà vu is so common, there is still a lack of understanding of its underlying reasons. What makes déjà vu difficult to study is the fact that it is a feeling not a physical phenomenon, meaning that it has no physical manifestation that could be observed [6]. Researchers must therefore rely on retrospective subjective accounts of people who experience it. Another issue is that it always happens without a warning and lasts only for a brief moment [6] and there is no identifiable external or internal stimulus that triggers it making it difficult to study in the laboratory [7]. Researchers propose several theories that might explain why déjà vu occurs, however no clear consensus has been reached yet.

One of the proposed explanations is the split (divided) perception theory [1, 6]. This theory proposes that perceptual experience is split into two parts, one that you are not aware of and one that you are aware of. This means that initially, you only process the event peripherally without dedicating attention to it due to being distracted by something else. However, this processing is immediately followed by a more complex processing once you fully attend to the stimulus. We might experience the first incomplete processing as a separate event resulting in déjà vu.

A somewhat related theory proposes that there might be a disruption in our neural pathways [1]. When we process an event, our brain receives many sensory inputs that are processed via multiple pathways. Thus, if there is a delay in processing via one of the pathways relative to the other, this can be interpreted as two separate events leading to the impression that the sensation that is happening now already happened in the past.

Another proposed explanation is the dual processing theory [4]. There are two different memory processes, recollection and recognition. Recollection is responsible for unambiguous recall of specific events while recognition is less specific and only elicits a feeling of familiarity. So, déjà vu might occur when there is a disagreement between these two processes. Recognition process produces an inaccurate sense of familiarity while the recollection process makes us accurately realise that the event did not actually occur.

Furthermore, researcher Cleary [2] proposed the similarity theory. According to her, déjà vu happens when the person is in a setting that resembles a previous experience which they cannot remember. Encountering a familiar object within that setting might trigger a feeling of familiarity which incorrectly generalises to the whole situation [1, 3, 6].

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To conclude,

Even though déjà vu is a common phenomenon, there is still a lack of understanding about its underlying mechanisms. Maybe we experience it because we truly encountered a similar situation before; maybe it is a result of dual processing or split attention; maybe a disruption in neural pathways is responsible. Whatever the cause is, it seems that it really is more than just a glitch in the matrix.

Extra resources:

1. Article: https://www.sciencefocus.com/the-human-body/my-deja-vu-is-so-extreme-i-cant-tell-whats-real-any-more/

2. Ted Talk by Dr. Anne Cleary: https://www.youtube.com/watch?v=nFAvUkjba-Q

References

1.     Brown, A. S. (2004). The déjà vu illusion. Current Directions in Psychological Science, 13(6), 256-259. https://doi.org/10.1111%2Fj.0963-7214.2004.00320.x

2.     Cleary, A. M., & Claxton, A. B. (2018). Déjà vu: An illusion of prediction. Psychological Science, 29(4), 635-644. https://doi.org/10.1177%2F0956797617743018

3.     Illman, N. A., Butler, C. R., Souchay, C., & Moulin, C. J. (2012). Déjà experiences in temporal lobe epilepsy. Epilepsy Research and Treatment, 2012. doi: 10.1155/2012/539567

4.     O'Connor, A. R., & Moulin, C. J. (2013). Déjà vu experiences in healthy subjects are unrelated to laboratory tests of recollection and familiarity for word stimuli. Frontiers in Psychology, 4, 881. https://doi.org/10.3389/fpsyg.2013.00881

5.     Penn Medicine. (July 2020). Feel like you’ve been here before? It might be déjà vu. Retrieved on June 11, 2021 from https://www.pennmedicine.org/updates/blogs/health-and-wellness/2019/july/deja-vu

6.     Raypole, C. (March 2020). What causes déjà vu? Retrieved on June 11, 2021 from https://www.healthline.com/health/mental-health/what-causes-deja-vu

7.   Thompson, L. (April 2016). You asked: What causes déjà vu? Retrieved on June 11, 2021 from https://vitalrecord.tamhsc.edu/you-asked-deja-vu-causes/?_ga=2.166562749.226426772.1579653874-1488221140.1579653874