Volume 8 (will be Vol 7 on site)


Déjà Vu: What Happens in the Brain
Ananya Sampathkumar 

 Abstract
Déjà vu is a common phenomenon that most healthy people experience. Despite its commonness, it is difficult to stimulate in a
lab situation, making information on this experience scarce. In order to combat this, researchers have come up with multiple
theories on where déjà vu takes place, what occurs, and why it actually happens. Researchers have also begun to study
mental disorders that involve déjà vu in order to possibly learn more about the elusive experience. Understanding déjà vu is
crucial to gaining a fuller understanding of memory, and how the brain reacts when memories are altered or off kilter; as further
technology is developed, scientists will be able to test out all theories surrounding déjà vu and narrow down the true cause.

Introduction
Despite the common manifestation of déjà vu in mental
illness, 97% of healthy individuals experience it (Khomutov et
al., 2023). Déjà vu is the French word for “seen before” and
refers to when an individual feels they are feeling an
experience identical to that they have lived before (Texas
A&M, 2016). 

Oftentimes, this feeling can be described as unnerving,
leading some researchers to incorporate déjà vu with what is
known as the “dreamy state.” The dreamy state is a term that
refers to the many symptoms (which can often be difficult to
distinguish between) that lead to the conscious being
distorted (Gillinder et al., 2022). Despite the commonality of
these emotions, there is very little known about déjà vu and
the other processes in the “dreamy state.” The main reason
for this is simple: these internal processes are very difficult to
study. According to Dr. Michelle Hook of Texas A&M, there is
“no clear, identifiable stimulus that elicits a déjà vu
experience (it is a retrospective report from an individual);
moreover, it is very difficult to study déjà vu in a laboratory”
(Texas A&M, 2016). As a result, there is very little that we
know about déjà vu as a phenomenon; however, there are
many different theories being explored surrounding the
feeling.

Where Déjà Vu Takes Place
When it comes to discussions of where déjà vu takes place, a
common theory is the optical system. For many, déjà vu is
triggered by seeing a specific object, place, person in their
visual system. From there, it is thought that these signals
were compared to current memories, thus causing déjà vu.
However, researchers have found proof of otherwise. In their
2006 study, Researchers Akira O'Connor and Chris Moulin at
University of Leeds studied a blind participant who claimed to
experience déjà vu. Being blind, the participant’s déjà vu was
caused by familiar sounds and smells that brought up
memories and part experiences such as a particular piece of
music playing as he unzipped a jacket (University of Leeds,
2006). This was the first time this particular situation was
reported, opening much discussion on the possible location
of déjà vu in the brain.

While the hypothalamus was not thought to directly play a
role in déjà vu, research has found that a stimulated
hypothalamus can also lead to the feeling of déjà vu. Andres
Lozano, Professor of Neurosurgery and Canada Research
Chair in Neuroscience, led the effort to experimentally treat a
man with morbid obesity through a DBS surgery. DBS stands
for deep brain stimulation, and this surgery often is used on
patients with movement disorders such as Parkinson’s
disease. Lozano and his team were attempting to identify
possible appetite suppressants in the patient’s hypothalamus,
and found that activating the electrodes caused the patient to
experience déjà vu. The patient reported a memory of being
with his friends in a park when he was 20, and as the
strength of the stimulation was increased, the description of
the memory got more detailed. This experiment was repeated
again in a double-blind situation, and the results also stated
that the participants experienced déjà vu. Researchers said
that the feeling of déjà vu increased as the part of the
hypothalamus closest to the fornix was stimulated. The fornix
is a group of fibers that carry signals within the limbic system
that is located close to the hypothalamus in the brain. Despite
this seeming to point to the fornix and hypothalamus’s
participation in the process of déjà vu, there is little research
surrounding their involvement in the processes behind other
“dreamy state” emotions (Wiley-Blackwell, 2008).

Additionally, there are several theories surrounding which
parts of the brain react to déjà vu stimuli. The main theory is
that it takes place in the corticolimbic network. The
corticolimbic network’s main functions are motor
programming and control, decision making, mnemonic
function and emotional regulation. The main parts of the brain
assumed to participate in the emotion of déjà vu are
hippocampus, rhinal cortices, parahippocampal gyri, and the
amygdala. The hippocampus is a part of the limbic system
that deals with episodic memory and spatial reasoning and
the rhinal cortices also generally work with memory and
object recognition. Specifically with déjà vu, the feeling that
you have experienced something before, the hippocampus
and rhinal cortices seem to be crucial. Furthermore, the
amygdala works with emotions and aggression and the
parahippocampal gyri works with memory retrieval and
encoding (Gillinder et al., 2022).



Even though it is difficult to place the exact places déjà vu
takes place in the brain, these parts of the brain are
associated with the “dreamy state” and déjà vu as a result. 

Possible Reasons for Déjà Vu
When it comes to déjà vu, scientists have a multitude of
theories as to why déjà vu occurs in the brain. One of these
theories is the electrical malfunction theory. This theory
proposes that déjà vu is a result of mismatched synaptic
transmissions. Seizures are often caused by many abnormal
electrical signals that interrupt the regular transmission of
typical electrical signals. However, any differences in
connections between nerve cells can cause a seizure in the
brain (John Hopkins, 2019). Patients with epileptic seizures
have said that they often experience déjà vu before a seizure;
seizures are often caused by dysfunctional neuron activity in
the brain. As a result, scientists theorize that déjà vu could be
caused by lesser malfunctions in neuronal activity (Texas
A&M, 2016). 

A second theory surrounding the occurrence of déjà vu is the
neural pathway mismatch. Brains are equipped to process a
certain amount of sensory information, but there is a lot of
information in the world. Due to sensory information being
classified as short term memory, scientists believe that long
term memory is engaged instead, causing the brain to pull
information from past memories and experiences (Texas
A&M, 2016). In the visual cortex, several pieces of
information travel through the neuronal pathways, with all of
them reaching the destination at the same time. Due to the
visual cortex processing the current information while the
sensory cortex processes past information, there is a
“mismatch” in the information between the two cortices,
causing the brain to believe that this situation is familiar
despite it being new.

The third theory is called the “glitch” theory. Scientists believe
that déjà vu could be caused by the neurons in the brain
mistakenly recognizing a stimulus and firing. This causes the
brain to confuse the past and present, and for the body to feel
déjà vu. This “glitch” is often compared to a hypnagogic jerk
(Texas A&M, 2016). Hypnagogic jerks happen when
someone is sleeping and their body involuntary jerks. These
two processes are similar in the way that the body is
experiencing one thing and the neurons fire for something
else (either a different experience or for wakefulness.)
 
The fourth theory is known as the split perception theory. The
idea is that the person perceives the same stimulus twice, but
in different states of true perception. The first stimulus is
perceived when distracted, quickly or in a period of delusion
of some sort, and as a result, the input is weaker than most
regular stimuli. This stimulus is then perceived again; this
time, the stimulus is grasped fully. This second viewing of the
stimulus causes our minds to believe that this stimulus is
strangely familiar in some way, but not being able to place
why as a result of the unregistered original stimulus. This
theory helps to explain why our brains would be unable to
place why we feel this moment has occurred before (Brown &
Marsh, 2010). 

However, when it comes to theories of déjà vu, it is incredibly
difficult to study and prove any of these methods with our
current technology due to the inability to replicate such
emotions in a clinical setting. As a result, scientists have
turned to other methods in order to gather information on the
elusive experience. 

Mental Disorders Related to Déjà Vu
Since déjà vu is challenging to replicate, scientists have
turned to other subjects to learn more about the phenomena
such as mental disorders. One mental disorder that has been
linked to déjà vu is anxiety. In a case study from 2014, a man
diagnosed with anxiety and depersonalization who
experiences extreme déjà vu was compared. In comparison
to other patients who experience déjà vu such as dementia
patients, this man was completely aware of his déjà vu
happening.

Figure 1. Brain visualization of several different systems in the
brain. Dorsal stream connects the parietal areas with

parahippocampal cortex. The rhinal cortices attaches to anterior
hippocampus, and the parahippocampal cortex attaches to posterior

hippocampus. Coloured dots represent neuronal activity areas in
the occipital and parieto-occipital cortex (Gillinder et al., 2022).

Figure 2. The neuron sets off an electrical impulse in order to
communicate with one another. Seizures are caused by abnormal

electrical activity (John Hopkins, 2019).

Brain Matters・Volume VII      6



He claims he was constantly living in a loop due to his
extreme déjà vu, and lived in constant anxiety. While this
case study does draw a possible link between déjà vu and
anxiety, the only evidence scientists currently have is
regarding the location of the neural signals. Both anxiety and
déjà vu take place in the hippocampal formation, which could
show a possible connection via location of signals (Wells et
al., 2014). However, there has not been enough research for
this possible connection to be confirmed. 

On the other hand, scientists have conducted a test on
patients with temporal lobe epilepsy and déjà vu. Scientists
tested 16 patients with temporal lobe epilepsy and tried to
evoke the “dreamy state” by stimulating the hippocampus and
amygdala. They did this in different ways: six patients had a
collective nine dreamy states as a result of seizures, 14
patients had a collective 43 dreamy states due to electrical
stimulation, and three patients had a collective five dreamy
states as a result of chemical stimulation. Furthermore, the
study shows that the amygdala was involved in 73% of
stimulation cases, the anterior hippocampus in 83% and the
temporal neocortex in 88% (Bancaud, Brunet-Bourgin,
Chauvel & Halgreen, 1994). Mental disorders that involve
déjà vu as a symptom are incredibly helpful in the study of
déjà vu due to the difficulty of stimulating déjà vu, and will
continue to aid in the research on déjà vu. 

Summary
While déjà vu is generally just described as a feeling of
having experienced something before, it is far more than an
emotion. Déjà vu is a complicated process that scientists do
not fully understand the purpose and reason for. Along with
déjà vu, there are several other similar emotions that are
often associated with déjà vu known as the “dreamy state.”
While we do not know much about the location of déjà vu,
scientists believe that this process takes place in the
hippocampus, rhinal cortices, parahippocampal gyri, and the
amygdala. There are four major theories as to how déjà vu
occurs in the brain: the electrical malfunction theory, the
neural pathway mismatch theory, and the “glitch” theory.
Despite all these theories, it is incredibly difficult to study déjà
vu due to the difficulty of stimulating the experience in a lab
situation. As science improves, we will get closer and closer
to understanding the mechanisms and purpose of déjà vu.

References
1. A&M, T. (2016, April 13). What causes Déjà Vu?.
ScienceDaily.
https://www.sciencedaily.com/releases/2016/04/1604131135
30.htm 
2. Bancaud, J., Halgren, E., Chauvel, P., & Brunet-Bourgin,
F. (1994). Anatomical origin of Déjà Vu and vivid “memories”
in Human Temporal Lobe Epilepsy. National Center for
Biotechnology Information.
https://pubmed.ncbi.nlm.nih.gov/8149215/

3. Gillinder, L., Chauvel, P., & Liegeois-Chauvel, C. (2022,
January 29). What Déjà Vu and the “Dreamy State” Tell Us
About Episodic Memory Networks. ScienceDirect. 
https://www.sciencedirect.com/science/article/abs/pii/S13882
45722001444
4. John Hopkins. (2019, November 19). 
Evaluation of a first-time seizure. Johns Hopkins Medicine.
https://www.hopkinsmedicine.org/health/conditions-and-
diseases/epilepsy/evaluation-of-a-firsttime-seizure
5. Khomutov, Kolesnikova, Mingazova, & Bespyatykh.
(2023). [personalized approach in the diagnostics and
treatment of symptomatic epilepsy with déjà vu seizures].
Stork. https://www.storkapp.me/pubpaper/37742269 
6. Marsh, E. J., & Brown, A. S. (2010, May 19). Digging into
déjà vu: Recent research on possible mechanisms.
Psychology of Learning and Motivation.
https://www.sciencedirect.com/science/article/abs/pii/S00797
42110530020
7. University of Leeds. (2006, November 29). 
A stunning new look at Déjà Vu. ScienceDaily.  
https://www.sciencedaily.com/releases/2006/11/0611281405
52.htm
8. Wells, C. E., Moulin, C. J., Ethridge, P., Illman, N. A.,
Davies, E., & Zeman, A. (2014, December 8). Persistent
psychogenic déjà vu: A case report - journal of medical case
reports. BioMed Central. 
https://jmedicalcasereports.biomedcentral.com/articles/10.11
86/1752-1947-8-414
9. Wiley-Blackwell. (2008, January 30). Deep brain
stimulation in hypothalamus triggers “Déjà Vu” memory recall
in patient. ScienceDaily. 
https://www.sciencedaily.com/releases/2008/01/0801300921
02.htm