Australasian Science: Australia's authority on science since 1938

All of This Has Happened Before

By Tim Hannan

A new case report shows that déjà vu can be persistent, debilitating and psychogenic.

While for the majority of us, the occasional impression that a novel scene or event is nevertheless somehow familiar is an odd, transient sensation, for rare individuals the déjà vu experience is both persistent and debilitating.

A recent paper in the Journal of Medical Case Reports has described a case of a 23-year-old university student who reported the impression that everything he experienced had occurred previously. This feeling was so intense that it caused him to stop watching television, reading newspapers and listening to the radio because he felt that he had seen or heard it all before. He described himself as terrified at being trapped in a time loop where he was reliving the past over and over again.

The French expression for “already seen” was first used in the late 1800s, but it was not until the mid-20th century that it became the common term. Conventionally defined as a transient mental state in which a person finds a novel experience to be somehow familiar, the systematic study of déjà vu presents significant challenges to researchers.

As a subjectively reported phenomena with no objectively verifiable behavioural response, investigation is largely reliant on retrospective surveys of participants’ experiences. However, these studies have provided inconsistent findings due to the inherent unreliability of asking people to estimate the frequency of an uncommon experience over an extended period.

Another method has been to study individuals with temporal lobe epilepsy or schizophrenia, who commonly report a higher incidence of déjà vu.

In temporal lobe epilepsy, déjà vu is described by some to be present during the aura preceding a seizure. Patients undergoing investigations of lesion location while conscious have also reported déjà vu during cortical stimulation. The experience appears to be particularly vivid for those with this form of epilepsy, and may be sustained for longer durations.

In the case of schizophrenia, while the sensation of unexpected familiarity of stimuli is sometimes reported, it is difficult to determine whether this experience is similar to déjà vu as experienced by others, or a symptom of a broader sense of depersonalisation.

Acknowledging these methodological limitations, it is nevertheless estimated that about 60% of the population describe experiencing déjà vu at least once in their lives, with around one-third of these reporting it to occur about once per month. No gender differences have been documented. The frequency is reported to decrease with age, but this may be because older adults are less inclined to admit to the experience: the lifetime incidence reported by older adults is notably lower than that of younger adults.

The dominant theory of déjà vu is that it reflects an error in the workings of the human memory systems. It is assumed that the normal retrieval of memories is facilitated by both perceptual cues and cognitive associations. When we perceive a stimulus (such as a scene, person or object), the brain automatically assesses its familiarity, and this enables the rapid retrieval of previously acquired, relevant information. If the stimulus is judged to be unfamiliar, this prompts increased and focused attention in order to gather and store potentially useful new information.

It is hypothesised that in déjà vu the assessment of familiarity is decoupled from the actual experience, so that the stimulus triggers a sense of familiarity without the retrieval of relevant information. The stimulus is felt to have been previously experienced, but simultaneously known to be unfamiliar. Support for this notion of a separation between the two processes is found in the experience of jamais vu, in which a person perceives a stimulus to be unfamiliar despite knowing that it has been previously encountered.

The increased frequency of déjà vu in temporal lobe epilepsy and some other neurological conditions has supported the hypothesis that it results from dysfunction in the neural systems that mediate memory, with the parahippocampal regions of the temporal lobe thought to be implicated.

However, a striking feature of the recent case is that, unlike others with persisting déjà vu, neurological investigations revealed no apparent organic pathology. Noting the student’s history of marked anxiety, the authors speculated that he may be the first reported case of a person experiencing persistent déjà vu from a psychogenic cause rather than organic pathology.

A/Prof Tim Hannan is Head of the School of Psychology at Charles Sturt University, and the Past President of the Australian Psychological Society.