What is déjà vu?
First defined in 1983, déjà vu (DV) is an exceedingly common mental state that is transitory in nature. Described as a ‘subjectively inappropriate impression of familiarity of a present experience with an undefined past’, it translates from French as literally as ‘already seen’. Colloquially, it is often used to describe familiar events or experiences, while in medical terminology it refers to the disconcerting perception that a novel experience is familiar.
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Clinically, DV is sometimes understood as a manifestation of a mental or neurological disorder, most commonly temporal lobe epilepsy (TLE) or schizophrenia. Epilepsy is a neurological disorder, caused by abnormal electrical activity within the brain and characterized by loss of consciousness and seizure. TLE is the commonest form of epilepsy, accounting for approximately 60% of all people with the diagnosis. This sub-type affects the hippocampal region, the area of the brain responsible for the processing and storage of short- and long-term memories, and research has shown a strong association between DV and seizures in people with TLE. The relationship between the two was first described in 1888 as a ‘dreamy state’ often co-occurring with TLE. Subsequently, a large body of research has shown that many individuals with TLE experience DV as a manifestation of the accompanying seizures, often immediately prior to convulsion.
In schizophrenia, experiences of DV may be longer, more intense and accompanied by feelings of depersonalization. Also referred to as derealization, it is a state of detachment whereby thoughts seem unreal and individuals feel as though they are external observers of themselves. However, when the prevalence of DV is compared between individuals with and without schizophrenia, the frequency of DV is higher in the neurotypical individuals. People with schizophrenia, however, experience DV as more distressing and disturbing, and are more likely to experience them when under physical or mental duress. A follow-up study by the same authors explored why schizophrenic people may experience DV less frequently and found an association between DV and negative symptoms of schizophrenia, and DV and antipsychotic medication.
Individuals with schizophrenia who exhibit more negative symptoms such as poverty of speech, reduced motivation and social drive have fewer DVs than those with fewer negative symptoms and healthy controls. It may be concluded that the brain dysfunction underpinning negative symptoms likely interferes with DV experiences. Conversely, the frequency of DV experiences is increased in the sub-sample of schizophrenic patients who are on higher doses of antipsychotic medication. Arguably, this may account for previous false associations between schizophrenia and DV. Furthermore, there is no obvious relationship between DV and positive symptoms of schizophrenia such as delusions and hallucinations, suggesting that DV experiences are not related to the mechanisms involved in these symptoms. Taking the results of these studies together, DV is thought to exist as a nonpathological phenomenon.
Nonpathological Theories of DV
Given that DV has a lifetime prevalence of 60-80% in nonclinical samples, it is clearly not always pathological. On the contrary, careful distinction between colloquial and ‘true’ experiences of DV in clinical contexts can separate a typical experience from a neurological or psychiatric condition. Warren-Gash and Zemen (2003) proposed a useful clinical assessment framework for distinguishing between pathological and non-pathological DV. These experiences should be assessed with respect to both frequency and type. Frequent colloquial DV and isolated and transient DV are considered normal. For experiences of ‘true’ DV to be indicative of pathology, they must be accompanied by other symptoms such as hallucinations, seizures, depression, anxiety or dissociation. Several theories pertaining to DV experiences in non-clinical samples have been suggested.
Such explanations assume that DV occurs when an individual has previously experienced a highly similar situation, memories of which have been processed and stored unconsciously rather than consciously. DV experiences are triggered when an element of the novel situation activates the unconscious memory, for example when a single element of an event is known, but the context novel. In these situations, the brain generalizes this familiarity, evoking the DV experience.
Neural Transmission Speed
This hypothesis is based on the speed with which information travels through the brain and describes the potential for processing errors in two pathways. In single pathway process errors, there is a delay in the transmission of a single piece of information to the brain, and a false sense of familiarity is triggered when the transmission is eventually delivered. In dual pathway errors, one pathway is delayed while the other functions normally. In this process, the DV experience is generated when focus between the two pathways changes rapidly.
This theory suggests that DV experiences are elicited when attention is divided between simultaneous perceptions within a single event. Whilst the brain is subliminally processing the environment, one singular observation is momentarily distracting and takes our full attention away from the environment. When it returns, the sensation of vague familiarity that is observed in DV is generated (Brown, 2004).
A definitive account for the phenomenon of DV remains elusive. Although not a core feature of mental illness, it can arise as part of a wider pattern of disturbance in some disorders. However, among healthy populations, explanations of DV mostly point to a temporary error in cognitive processing.
- Adachi T, Adachi N, Takekawa Y, Akanuma N, Ito M, Matsubara R, Ikeda H, Kimura M, Arai H. Déjà vu experiences in patients with schizophrenia. Compr Psychiatry. 2006 Sep-Oct;47(5):389-93. Epub 2006 Apr 19. https://www.ncbi.nlm.nih.gov/pubmed/16905402
- Adachi N1 Adachi T, Akanuma N, Matsubara R, Ito M, Takekawa Y, Ikeda H, Arai H. Déjà vu experiences in schizophrenia: relations with psychopathology and antipsychotic medication. Compr Psychiatry. 2007 Nov-Dec;48(6):592-6. Epub 2007 Aug 20. https://www.ncbi.nlm.nih.gov/pubmed/17954146
- Brown AS. The déjà vu illusion. 2004. https://doi.org/10.1111/j.0963-7214.2004.00320.x
- Illman NA, Butler CR, Souchay C, Moulin CJA. Déjà experiences in temporal lobe epilepsy. Epilepsy Research and Treatment. Volume 2012, Article ID 539567
- Neppe VM: The psychology of déjà vu: have i been here before?: 1-277 & I-XLV. Johannesburg, Witwatersrand University Press, 1983.
- O’Connor AR, Moulin CJA. Déjà vu experiences in healthy subjects are unrelated to laboratory tests of recollection and familiarity for word stimuli. Front. Psychol., 27 November 2013.
- Warren-Gash C, Zemen A. Déjà vu. Pract Neurol., first published 1 April 2003.