Deja Vu: What It Is, When It May Be Cause for Concern
Déjà vu is a brisk, stunning sensation of having already lived a totally identical situation in some undefined past. The feeling that you’ve done this exact same thing once before — been in this place, engaged in this conversation — overwhelms you.
At the same time, you’re clearly aware that this cannot be reality because you have never been in this place or met these people at any time in your past.
Sixty to 70 percent of healthy people experience this transitory mental state. A peculiar visual context most often triggers déjà vu, although spoken words alone sometimes create the illusion of familiarity.
Déjà vu occurs most often between 15 and 25 years of age and decreases progressively with age. People who have more education, who travel, who remember their dreams and who hold liberal beliefs are more susceptible to it. Among students, fatigue or stress may facilitate déjà vu. Déjà vu also occurs more frequently on evenings and weekends.
Insight into how déjà vu happens
Déjà vu can also be a neurological symptom. The same sensation, with exactly the same features, is often reported by patients with temporal lobe epilepsy.
Recordings of the brain prior to surgery for temporal epilepsy offer some insight into the mechanisms of déjà vu. In the brain, part of the temporal cortex lies just below the hippocampus. Seizure discharges from this temporal cortex simultaneously activate two circuits in the hippocampus.
One circuit monitors our ongoing experience of the outer world. The other retrieves past memories. The simultaneous activation compresses time between the two brain functions, causing us to “remember the present,” or experience déjà vu.
When déjà vu signals a problem
Déjà vu may suggest a neurological problem when it:
- Occurs frequently (a few times a month or more often versus a few times a year)
- Is accompanied by abnormal dream-like memories or visual scenes
- Is followed by loss of consciousness and/or symptoms such as unconscious chewing, fumbling, racing of the heart, or a feeling of fear
If there is any doubt about the cause of déjà vu, it is important to consult a neurologist.
Apart from epilepsy, déjà vu has been observed in vascular dementia and more rarely in other dementias. Patients with fronto-temporal dementia experience persistent déjà vu and fabricate stories about their current life to rationalize the illusion.