Unveiling the Mystery of Deja Vu

(study summary)

Study shows differences in gray matter between brains of people experiencing deja vu and control subjects. These are most prominent in hippocampi and surrounding areas, which have been linked to deja vu before. Due to structural similarities between "healthy" deja vu subjects and mesial temporal lobe epilepsy patients, authors of the study suggest deja vu experiences in healthy patients might be caused by "small seizures". 

The "error in the Matrix" hypothesis has a serious rival 

Deja vu is an eerie experience during which you get the impression a situation is familiar even though you know the feeling of familiarity is inappropriate. It occurs both in healthy subjects and as a manifestation of brain disease, particularly temporal lobe epilepsy. Various theories of how deja vu originates have been suggested, for example “the theory that a disruption of attention or perception leads to anomalous ‘dual’ processing of sensory information” - which would cause information to be processed both as a percept and as a memory.

This study shows how brains of people with frequent deja vu experiences differ from brains of non-deja vu controls in the amount of gray matter in certain parts of the brain. Deja vu subjects had significantly less gray matter in areas like insular cortices, superior temporal sulci, basal ganglia and thalami, the most striking differences occuring in hippocampi and hippocampal gyri. This pattern resembles brains of patients suffering from mesial temporal lobe epilepsy. 

Parahippocampal region has been associated with “feeling of familiarity” in healthy subjects and previous research has shown that stimulation of this area in epilepsy patients mostly leads to deja vu. However, deja vu has also been evoked by deep-brain stimulation, which suggests subcortical structures play an important role too. 

 Hippocampus is an exceptionally fragile structure prone to damage from inflammation, sleep deprivation and psychological stress, esp. during early development. A widespread alteration of neural networks appears to be present in both pathological and non-pathological deja vu subjects. This could mean deja vu experiences in both healthy subjects and mesial temporal lobe epilepsy patients share common origin and deja vu experiences in "healthy" subjects might be actually caused by “small seizures”.

Brázdil M, et al., Unveiling the mystery of deja vu: The structural anatomy of de ja vu, Cortex (2012), doi:10.1016/j.cortex.2012.03.004