What happens in brain during deja vu? Experts decode memory glitch

Experts explain how deja vu arises from brief memory glitches in the brain, why it is usually harmless, and when frequent episodes could signal something serious

  It often arrives without warning. You walk into a room, hear a sentence, or experience a moment that feels eerily familiar, even though you know it cannot be. This strange sensation where you feel like you have experienced a particular moment before, known as deja vu, can be both fascinating and unsettling. While many brush it off as a harmless quirk of the mind, neurologists say it offers a rare glimpse into how the brain processes memory, and how it occasionally gets it wrong.

 

What causes deja vu in the brain?

 

“A deja vu, French for ‘already seen’, is a striking cognitive phenomenon where a novel experience feels uncannily familiar,” explains Dr Furqan Khan, consultant neurologist at Saifee Hospital. He adds that while it is common and usually harmless, it reveals how memory systems can briefly malfunction.

 

 

At the centre of this experience is the brain’s medial temporal lobe, which plays a key role in memory. Within this network, different regions perform distinct functions but work closely together.

 

• The hippocampus helps encode and retrieve memories
• The parahippocampal cortex detects familiarity
• The temporal neocortex processes sensory input
• The prefrontal cortex checks whether a memory is real or misplaced

 

Deja vu occurs when these systems fall out of sync. As Dr Khan puts it, “The brain says ‘this is familiar’ before it can verify why.” This momentary disconnect means the feeling of familiarity appears without an actual memory to support it.

 

Why does the brain signal false familiarity?

 

Experts do not point to a single cause of déjà vu. Instead, they suggest that several well-researched theories may explain why the brain suddenly signals familiarity without a clear reason.

 

1. Memory mismatch theory

This suggests that the brain’s familiarity system is triggered, but it cannot retrieve a specific memory to match it. As a result, you feel like you have experienced the moment before, even though you have not. Studies using brain imaging, along with research on epilepsy, strongly support this idea.

"Deja vu is not a failure of memory itself, but rather a mistake in how memory is processed," Dr Khan explains, "It is a metacognitive error where the brain briefly mislabels the present as the past."

 

2. Dual-processing delay theory

In this case, there is a slight lag in how the brain processes incoming information. One pathway registers the experience first, and when the second catches up moments later, the brain mistakenly interprets it as a repeated event.

 

3. Pattern recognition

Sometimes, a current situation may resemble fragments of past experiences, such as a similar layout, smell, or conversation. Even if you cannot consciously recall the original memory, your brain detects the similarity and creates a sense of familiarity.

 

4. Temporary neural misfiring

This may happen when there is a brief surge or misfiring of electrical activity in memory-related brain circuits, creating a false signal of familiarity. Dr Sushma Sharma, programme clinical director – Neurology at Marengo Asia Hospitals Faridabad, notes, “A temporary glitch in these neural networks triggers this false familiarity feeling.” She explains that misfiring electrical activity in the temporal lobe plays a crucial role.

 

Similarly, Dr Jaya Sukul, clinical psychologist and founder of Headspace Healing, Noida, highlights the role of brain chemistry. “High levels of dopamine, which is associated with feelings of familiarity, can cause neurons to misfire and create this feeling,” she says.

 

Another related phenomenon, which highlights how fragile this system can be, is jamais vu. Jamais vu, meaning “never seen”, is the opposite of deja vu and occurs when something familiar suddenly feels strange or unrecognisable, often due to a temporary disruption in how the brain retrieves stored memories.

 

When is deja vu harmless and when should you worry?

 

For most people, deja vu is occasional and short-lived. It tends to occur during periods of fatigue, stress, or excitement. Importantly, individuals remain aware that the sensation is unusual and not real. Experts describe this as normal, and it does not require medical attention.

 

However, not all experiences are harmless. When deja vu becomes frequent or intense, it may signal an underlying neurological issue.

 

Doctors point to several warning signs:

 

• Episodes occurring multiple times a week
• Prolonged sensations lasting more than a minute
• Repetitive, identical experiences
• Olfactory hallucinations (burning smell)
• Associated symptoms such as confusion, loss of awareness, or unusual body movements
• Rising epigastric sensation - sudden, unusual feeling in the stomach that seems to move upwards
• Involuntary, repetitive actions such as lip smacking, chewing, or hand movements
• Feeling disoriented or unable to recall what just happened after the episode

 

Dr Sukul adds that warning signs can also include “intense fear or dread, strong unconscious repeated behaviour like lip smacking, and a rising feeling in the stomach.”

 

What conditions are linked to frequent deja vu?

 

While most deja vu episodes are harmless, experts note that frequent or intense experiences may sometimes be linked to underlying conditions, particularly when they follow a pattern or occur with other symptoms.

 

1. Temporal lobe epilepsy

Dr Sharma explains that recurrent episodes accompanied by confusion or loss of awareness could indicate temporal lobe epilepsy. In such cases, deja vu may actually be a type of seizure aura, sometimes followed by more severe symptoms such as convulsions.

Treatment typically includes anti-seizure medications such as levetiracetam or lamotrigine, and in some cases, surgery.

 

2. Anxiety and stress-related disorders

These can trigger deja vu through attentional fragmentation and memory mismatch, especially during periods of fatigue or emotional strain. Management may involve cognitive behavioural therapy (CBT), medication like SSRIs, and stress management techniques.

 

3. Dementia-related conditions (rare)

More commonly linked to deja vecu, where individuals feel they are reliving past events. This is associated with impaired reality monitoring and difficulty distinguishing present experiences from memories.

 

Understanding these distinctions is important, as it helps separate benign, occasional déjà vu from patterns that may require further medical attention. Doctors may recommend the following for further diagnosis:

 

• EEG (electroencephalogram) to assess electrical brain activity
• MRI scans to identify structural abnormalities
• Additional psychological or metabolic assessments if needed

 

“The treatment for each condition varies, so consulting a neurologist is essential to identify the cause of deja vu and decide the appropriate course of treatment,” adds Dr Sukul.

 

Is déjà vu usually harmless or a warning signal?

 

Experts share that 70-90 per cent of people experience deja vu at least once in their lifetime. In most cases, it is simply a fleeting glitch in an otherwise healthy brain.

 

Yet, when it occurs repeatedly or alongside other symptoms, it can serve as an early warning signal. Understanding the difference is key, because while déjà vu is often harmless, the brain may sometimes be signalling something more serious.     

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This report is for informational purposes only and is not a substitute for professional medical advice.