The 72 different proposed explanations for déjà vu are examined. Broadly 50 were hypothesized before 1979 and another 22 were brought forward thereafter. These show the many explanations for the concept, but they do not illustrate the scientific mechanisms with which to approach déjà vu. These explanations may ultimately express themselves phenomenologically in a limited number of ways and these explanations may commonly overlap.

Keywords:Associative Déjà Vu; Chronic Déjà Vu; Confabulation; Continuous Déjà Vu; Definition; Déjà; Déjà classification; Déjà experiences; Déjà subtypes; Déjà terminology; Déjà vu; déjà vu books; History; Memory; Modern era; Multidimensional scaling; Neppe; Phenomenology; psi; Psychodynamic; Psychotic Déjà Vu; Redintegration; Restricted paramnesia; Schizophrenic Déjà Vu; SPE Déjà Vu; Subjective psi experience Déjà Vu; Temporal Lobe epileptic Déjà Vu; TLE Déjà Vu

 To understand the variability of the explanations, we should remember that until 1979, a major research and classification problem was the inconsistency in eliciting déjà vu: Consequently, data interpretation became difficult. At that time, there were only the 11 kinds of déjà experiences described earlier in this series, such as, déjà fait-already done, déjà pensé-already thought and déjà raconté-already told [1].

Paradoxes abounded at that point: Déjà vu occurred at least once in the lifetimes of two-thirds of ostensibly "normal" individuals [2,3]; yet in medical schools, it was taught routinely that déjà vu was a symptom in temporal lobe epilepsy (TLE) [4]. It was also reported in ‘subjective psi experients’ who often would supply intense descriptions [5]. Additionally, Neppe raised the question: was there a special kind of déjà vu in psychotics? [2] The time was ripe to examine whether déjà vu was a single phenomenon or phenomenologically distinct in these populations, and, if so, in what way.

Despite the overlap of déjà experiences in different ‘nosological’ (read as synonymous with ‘classification’) subtypes, Neppe made the comment that some of the déjà experiences are particularly common in certain of these nosological subtypes.

Let’s try to correlate how the most commonly located déjà subtypes correlate with the subtypes of déjà experience. This is based phenomenologically on the Neppe research and also clinically on real life experience [3,6].

In all, no fewer than 72 such ideas can be extracted from the literature on déjà vu [7,8]. Because so many (and often related) explanations appear, we shall merely survey the most popular or important. These explanations are just interpretations and it’s interesting to see how and when the concepts developed.

In Tables 4A, 4B, 4C, 4D and 4E, I separate into easy steps the different explanations prior to 1979. These explanations are listed in the Neppe books Déjà Vu Revisited [9] and The Psychology of Déjà Vu [3]. In Table 4F, 4G, 4H, 4I and 4J, the 22 explanations since 1979 are discussed, with 21 derived from Déjà Vu A Second Look [6].

Later Subjective Psi Mechanisms [6]^b

We should not neglect the early contributions. Many of them focus on what we now call associative déjà vu and range from psychoanalytic explanations, to explanations of compensating for anxiety, to memory distortions, to depersonalization, to minimal delays in transmission of information, to the part reinstating the whole (redintegration). Some specifically spoke about the paranormal, though this was comparatively rare.

In my 1981 PhD thesis [2], in my 1983 book The Psychology of Déjà Vu, [3] and then in the reformulation of that 1983 book, a companion volume for this book entitled Déjà Vu Revisited, [3] I pointed out the 50 different explanations or phenomenological mechanisms for déjà vu that prevailed at the time and have listed them above. Subsequently, several more related theories have been developed. Whether to accord these the status of full theories depends on the slant.

I cannot sufficiently overemphasize the fallacy of the conclusion that, because there may now be at least 72 different explanations for déjà vu and one of them is right, then the other 71 of them must be wrong. It is almost like saying ‘I am only allowed to have one mechanism for thought, not 72 different mechanisms for thought.’ Indeed, the great majority of these mechanisms are possibly correct, but incompletely so, having elements of truth:

They may ultimately express themselves phenomenologically in a limited number of ways-for example, associative, subjective paranormal, temporal lobe, psychotic and/or other organic including a chronic persistent or continuous variation. The mechanisms therefore have been arbitrarily classified under different headings. However, it is possible; for example, that some mechanisms classified pathologically-for example, frontotemporal limbic disconnectedness-may have relevance in the ordinary ostensibly normal individual’s déjà vu.

Conversely, mechanisms that appear relevant for the general population and predominantly reflect associative déjà vu may overlap over all categories of déjà vu. There is no reason why the temporal lobe epileptic or the organically impaired patient or the well-controlled psychotic patient should not have their déjà vu correlated with the associative mechanisms hypothesized below. Similarly, there is no reason why such associative déjà vu may not have complex etiologies with psychodynamic precipitants of underlying memory distortions triggered by differently functioning frontotemporal connections. On the other hand, of course, some of these mechanisms are unproven and may turn out to be incorrect. Nevertheless, given that they appear in the published literature, I have attempted to make this as complete a listing as possible.

^bWhereas Neppe uses the phrase ‘subjective psi’ to emphasize the neutral, non-prejudicial connotation, the term ‘paranormal’ is far more frequently used and this term has been maintained for other authors in their desciptions of déjà vu.

After careful consideration, I believe the following 21 should be added to the original 50 mechanisms:

Effectively, this makes for 72 major theories explaining déjà vu.
As pointed out earlier, each proposed mechanism does not imply that all are correct, nor that any one necessarily excludes any other. For example, a predisposing factor of redintegration (the part-reinstating-whole mechanism) combined with restricted paramnesia (only part-recognitions of past memories producing déjà vu distortions) may exist and this may produce déjà vu only under specific circumstances associated with a need for anxiety relief.

These mechanisms may, at times, set the framework particularly for associative déjà vu given the correct precipitators. However, this may even require a precipitating trigger for the déjà vu experience, such as that mild acute anxiety being relieved by the déjà vu, or alternatively fatigue that precipitated the poor memories, or simply exposure to a new situation which may be unexpected. Any combination of these may be relevant features for associative déjà vu experiences [3]. Clearly, other subtypes may also apply. Abnormal firing in the brain may trigger déjà vu, but that particular stereotypical path of firing in the brain may require an environmental trigger. Subjective psi experiences may be triggered by long-forgotten memories of a specific place and this may be interpreted as “psychic” and may have many elements that are subjectively pertinent given the previous experiential milieu of the subject. A psychotic patient may have limited reality contacts and may misinterpret their realities, sometimes quite idiosyncratically, but there may still be that anxiety or redintegrative mechanism that may begin the process. And someone with a dementing condition may persistently experience the present with an undefined past and confabulate that past. The difficulty may be whether the memory distortions are of such a kind that they can be interpreted as déjà vu in the first place!

Déjà vu must be regarded as symptomatic of many causes, each different. The early history of mechanistic expression of déjà vu involved Zangwill and Chari. Neppe discusses the eight modern mechanisms for déjà vu allowing analysis of the 72 explanations plus leading to the development of the four subtypes that incorporate these mechanisms.
 The 36 different déjà experiences are linked with the four features of the four different déjà vu subtypes. Examples of the qualitative differences are provided.

Classification of Déjà Vu

As shown in the previous section, most authors on déjà vu have tried to derive or explain the déjà vu phenomenon from a single pathology or etiology. They then have proposed explanations; though the majority of the 72 do not have a solid basis and yet many have regarded déjà vu as due to one particular cause.

This is clearly untenable. Déjà vu must be regarded as symptomatic of many causes, each different. As such, a system of classification of déjà vu becomes obligatory, which will involve an attempt to differentiate the déjà vu experience within this classificatory system [1].

Apparently, the only two real early attempts to classify déjà vu experience in the published literature are those of Zangwill [76] and Chari [50,51]. Zangwill discussed two subdivisions namely, endogenous and reactive Déjà Vu [76]. Endogenous means internal, reactive refers to responses to the environment.

Endogenous paramnesia

‘Endogenous paramnesia’ was a paramnesic experience associated with a memory disorder of mental synthesis. Zangwill’s endogenous experience was approximately synonymous with organic neuropathological causes of déjà vu [76]. Zangwill cautioned that a psychogenic explanation for endogenous déjà vu was incorrect and should not be attempted. His organic bias was strengthened by Penfield’s 1958 experimental induction of dreamy state seizures by electrical stimulation of the temporal lobe [23]. This conclusively illustrated the occurrence of endogenous déjà vu.

Reactive déjà vu

Reactive déjà vu was precipitated by some ‘specific peculiarity of the setting or environment’. Reactive déjà vu included theories which postulated a psychological linkage of the present with the past. It did not, therefore, presuppose any ‘true impairment of mental syntheses. The bulk of modern day hypotheses on the origin of reactive déjà vu derive from the psychoanalytic theories of déjà vu.

Zangwill’s dichotomy of endogenous and reactive déjà vu certainly differentiated two major areas [76]. It had, however, limited application for a clinico-pathological classification, because etiology, symptomatology, diagnosis and prognosis were not unified. Also, his dichotomy may well have been too simplistic. For example, ‘déjà vu with subjective psi experiences’ was ignored, as was any further sub classification of organic experiences.

Chari’s Classification

Professor C. T. K. Chari’s classification of déjà vu [50,51,77] was certainly broader than Zangwill’s [76]. He distinguished three kinds of déjà vu experience, the first two of which are difficult to accept in the form presented.  

Pathological and abnormal cases

Chari felt that déjà vu manifested pathologically in a wide variety of psychopathological diagnoses. He cited the alcoholic psychoses, migraine, schizophrenia and paranoia, epilepsy, general paresis of the insane-a late stage of syphilis and neurosis. His justification for the choice of these diagnostic groups was that déjà vu had been reported in these conditions. He considered the essential feature of the déjà vu experience in these abnormal cases to be impaired awareness of one’s memory of surroundings (persons and objects). [50,51] Chari, however, did not adequately defend this obscure opinion [3,20].

Normal déjà vu

Chari gave the example of MacCurdy’s ‘perplexity psychoses’ [10]. He felt that déjà vu was initiated by certain environmental elements of the past resembling the present and could sometimes be activated by fatigue or decreased attention. Thus, he indirectly equated ‘normal déjà vu’ with the ‘restricted paramnesia’.

Precognitive déjà vu / telepathic déjà vu

1. come in successive waves;
2. reach great intensity at times, increasing to a climax;
3. involve an illusion of reliving a total situation;
4. evoke a ‘turmoil of memories’ and a marked affective response congruous with this, which lasts a few minutes (not a mild perplexity as in the normal group);
5. Have precognitive components.

Credit should be given to Chari for his pioneering attempts at suggesting qualitative parameters for this particular kind of déjà vu experience [50,51]. He extracted his data from case reports of alleged precognition and claimed reincarnation [50,51]. We have established that there are 36 different déjà experiences. However, these do not have diagnostic relevance, though some may fit more within certain subtypes.

Several relevant questions arise: Are there different déjà subtypes or just one way to adequately explain all déjà experiences? [78,79] For example, is déjà vu a subjective psi experience (SPE)? And can we apply the methodology used for analyzing déjà experience to the discipline of ‘Consciousness Studies’? [79].

This introduces a second axis: The nosological subtypes of déjà vu. This means that the causes, origin and population distribution may be distinct and usually separate, although technically one individual could have more than one kind of déjà vu. We examine the four major ones later, with a questionable fifth diagnostic category.

First based on the literature, there are eight categories of mechanism of déjà vu:

Everybody from parapsychologists to psychoanalysts has suggested mechanisms for this common sensation but different researchers tend to place it within varying conceptual models. In this respect, déjà vu experiences can be interpreted in the fabric of eight different mechanisms as in Table 5A.

Within these eight mechanisms, we could analyze 72 current different explanations for déjà vu. There is overlap. But some of these are purely theoretical; others may occur but are unlikely or inappropriate. Almost all of these causes can broadly be characterized within the “psychological” (including psychodynamic, memory and psychotic), ‘cerebral’ (paroxysmal, focal or hemispheric), or ‘paranormal’ (including reincarnation, precognition and distortions of time) groups [78,79]. Because so many (and often related) explanations appear, we shall merely survey the most popular or important. It will soon become clear that no single hypothesis can explain the wide range of déjà vu occurrences. Déjà vu is simply not a single, unitary phenomenon.

I briefly list below and apply data from multiple publications [3,6,77,20,80-87]. In essence, déjà vu cannot be understood unless we first place the experience within the appropriate explanatory category. Is it a psychological, neurological or parapsychological experience?

First we examine the 8 major hypothesized mechanisms in Table 5A

What is the difference between describing explanations and mechanisms? The 72 explanations are attempts to explain how déjà vu occurs. Many of these are linked up with the eight major subdivisions that Neppe suggests are possible ways in which déjà vu occurs [3,6,20]. These mechanisms in turn are hypothetical constructs that fit the four major nosological subdivisions. In one of these four, Associative déjà vu particularly, there are several ways in which déjà vu may occur (#1-5 in Table 5A above). Currently, we think that the cause in these instances may be multifactorial involving several different mechanisms. None of these mechanisms are exclusive to subgroups and, for example, disorders of memory, may explain the confabulatory elements attributed to the so-called and controversial Alzheimer, chronic subtype; and psychotic misinterpretations may explain a continuous déjà vu.

Significant important differences exist in the expression of déjà vu in the different subject populations reflecting the four different nosological subtypes. This article gives some brief examples and explanations andalso illustrates the complexity of the descriptions and their analyses and the phenomenology of these experiences.
Neppe hypothesized and then, by applying multidimensional scaling in 22 dimensions, empirically demonstrated four phenomenologically distinct nosological subtypes representing four different, distinct populations motivating four, etiologically distinct kinds of déjà vu: subjective psi experience (SPE) déjà vu (in SPE experients), associative déjà vu (in ostensible “normals” [subjective psi non-experients] and also in non-epileptic temporal lobe dysfunction and non-temporal lobe epilepsy patients), psychotic déjà vu (in schizophrenics) and temporal lobe epileptic (TLE) déjà vu in TLE patients. The approach used serves as a model for phenomenologically relevant analyses in neuroscience, psychology, psychopathology and parapsychology. This allows standardized, relevant recordings. This also requires development of further appropriate questionnaires to ensure phenomenological homogeneity in further research and meta-analyses. Phenomenological detailing ensures a methodology of ensuring that data is recorded in as standardized and relevant a way possible.

As we’ve seen, Dr Vernon Neppe has delineated seventy-one logical scientific explanations for the mechanism of déjà vu. Most are simply incorrect as there is no basis for them. Sometimes the models overlap, as with the Brown [88] and Banister [89,90] work below. And to complicate more, as we’ve seen, the déjà vu phenomenon is possibly the most misused of all terms, because it’s a fashionable way to talk about information repeating itself [3,6,20]. At this point, there are nearly 2000 useful articles on déjà vu. Many are listed in Neppe’s ‘Déjà Vu Glossary and Library’ [83], but, of course, updated since then. This section briefly chooses some modern highlights in research in déjà vu. This gives a taste of key work but without overwhelming [91].

Applying Qualitative Phenomenological Research

The stimulus for the modern differentiation into demonstrable subtypes began in 1971. While a medical student in 1971, Vernon Neppe was intrigued by several contradictory paradoxes. He learned in his psychiatry course that déjà vu was symptomatic of temporal lobe epilepsy, yet his further research showed that 70% of the population had this experience [92]. He noted that something like déjà vu can be induced either by hypnosis or by electrical stimulation of the brain’s temporal lobe. Neppe wondered whether so-called “psychics” were having a different kind of experience.

Could it be that déjà vu is really not a single phenomenon but that several different types exist? Could the sensation originate in several differing ways? And could some déjà vu experiences be normal to us while others represent pathological processes at work?

It is remarkable how little research had been addressed to these issues by 1980. This paucity of data, nevertheless, helped guide Neppe’s own research as part of his doctoral work at the University of Witwatersrand in Johannesburg, South Africa [2]. Neppe began by studying the way different groups of people described déjà vu experiences.

This led Vernon Neppe (1979) [2,3] to analyze déjà vu in detail phenomenologically, so qualitative differences could be elicited in possible subtypes.  Neppe developed a Déjà Vu Questionnaire to adequately screen for the many instances of déjà experiences. He added names to nine (at that point unnamed) circumstances in which déjà vu could occur. Coincidentally, two of these déjà experiences were also independently being described by Art Funkhouser in Switzerland-déjà rêvé- already dreamt and déjà visité-already visited (a locality). Therefore, Neppe was able to study the 21 known kinds of déjà vu experiences in his phenomenological analyses [3,6,79]. He administered a screening and a detailed questionnaire, the latter to analyze phenomenological differences. This was combined with detailed interviews including specific examples.

Self-proclaimed psychics report frequent déjà vu experiences and their experiences did not seem to be pathological. This reflected those who reported subjective psi experiences based on specific, detailed criteria for subjective validity and specificity [3,79]. Neppe, therefore, collected several such cases. He compared two groups from the same membership organization.

First, there were ‘ostensibly normal people’ who claimed no psychic abilities so-called ‘Subjective Psi Non-Experients’. Their déjà vu reports were compared with a second distinct population of: ostensible normal’ but they reported many psychic experiences that they interpreted as such and therefore were called ‘Subjective Psi Experients’. Like all déjà vu reports, the descriptions in both instances were subjective, neither confirming nor denying the objective validity of their experiences. But the key question was did each have a distinct kind of déjà vu? [3,79].

Neppe also looked at the déjà vu reports of schizophrenics and epileptics [3,79]. This constituted a second comparative population, this time a neuropsychiatric population of temporal lobe epileptics, a subtype of all epileptics that he postulated would be specific: He also included other non-temporal lobe epileptics and then compared the temporal lobe epileptics with a schizophrenic population who did not exhibit overt psychosis but were sufficiently ill that they had been hospitalized. He included a further group of non-temporal lobe epileptics and those who were not epileptic but had temporal lobe dysfunction. He postulated they would have the same déjà vu experiences as the ‘Ostensibly normal Subjective Paranormal Non-Experients’. Theywould therefore appear rather like that ordinary, normal kind of déjà vu, as there would be no firing specifically in the area of the brain that would cause them to experience this déjà vu awareness that it had happened before. Importantly, in all these subjects, special carefully evaluated criteria were used in the whole available population at the pre-defined times, so that comparisons could be made.

Graph representing the differences between the 5 Groups based on the five-point qualitative parameters of déjà vu. (Distance between two column points approximates the Euclidean distance between the two columns as vectors in R22)

It was very important to differentiate this because otherwise one would ask: if a person has a seizure and they have a particular aura, but the aura is frontal lobe, for instance, could the person be experiencing the same aura and thinking that it is déjà vu? Would it be that this subgroup of epileptic would know it was not déjà vu because they would experience the appropriateness of the experience and perceive it as logically different?

The complexity of the phenomenon and the lack of consensus in the literature-as well as the relative dearth of scientific study of déjà vu-led Neppe in 1981 to develop a questionnaire-the Neppe Déjà Vu Questionnaire. This had two major components: The Screening Questionnaire portion attempted to ensure that déjà vu experiences were being screened for in a broad enough fashion. Secondly, the Qualitative Questionnaire section that followed was designed to gather specific details about the subjects’ déjà vu experiences [3]. This 1981 questionnaire consisted of 86 items. Neppe asked each informant to detail his or her experience [2,3]. He explored the circumstances under which the episode was perceived, the perceptual quality of the déjà vu, changes in thinking that accompanied it, intensity, clarity, emotional level and any associated and possibly paranormal factors and so on.

Neppe hypothesized that there would be four phenomenologically distinct nosological subtypes in his four comparative subpopulations. This hypothesis was, indeed, demonstrated by applying multidimensional scaling in 22 dimensions using median column geometry, to the data. Effectively, the statistician, Dr Dan Bradu, used a cutting edge technique to analyze mathematically 22 dimensions and produce a geometric visual of the result. (Figure 6a represents this and Figure 6b and 6c shows visually the graphic differences between the different groups. Specifically and remarkably, but also fortunately because it eliminated debate, the four different nosological déjà vu subtypes were represented in the defined populations in four different quadrants [3,38,79]. With all four quadrants represented, we were able to demonstrate that there was an existence of the four nosological subtypes [3]. This was predictable across diagnostic categories and we could classify these different symptom categories as qualitatively different amongst the four. Neppe called the four distinct and hypothesized categories: Subjective paranormal (SPE) déjà vu, Temporal lobe epileptic (TLE) déjà vu, Schizophrenic (later called, Psychotic) déjà vu and Associative déjà vu [3].

These subtypes strongly motivated for four, etiologically distinct kinds of déjà vu subtypes occurring in these four different populations (subjective psi experience (SPE) déjà vu (in SPE experients), associative déjà vu (in ostensible “normal’s” [subjective paranormal non-experients] and also in non-epileptic temporal lobe dysfunction and non-temporal lobe epilepsy patients), psychotic déjà vu (in schizophrenics) and temporal lobe epileptic (TLE) déjà vu in TLE patients.) [3,38,79].

Figure 6A shows multidimensional scaling and the graph showing median column geometry representing the differences between the four different quadrants. This has five groups because the non-temporal lobe epileptics and the non-epileptic temporal lobe dysfunctions (OE-TLD) were studied as a separate group, and, as hypothesized, this population fitted into the subjective paranormal non-experience group. Their results were very close and this itself was very useful because it shows the linkup of the neuropsychiatric with the so-called “normal” sub-population in this regard implying a certain unified population. SPE = Subjective paranormal experients; TLE = temporal lobe epileptics.

The graph represents differences between the five groups based on the five-point qualitative parameters of déjà vu. The distance between two column points approximates the Euclidean distance between the two columns in R [22] vectors. Experts looking at this graph could argue that Psychotic Déjà Vu (SCH) is not too different distance-wise in R [22] from the subjective paranormal non-experience Déjà Vu (SPNE) (= Associative Déjà Vu) but we have to examine not only the major distance between the two, but the qualitative differences (Figure 6B). However, this graph is a 2 dimensional representation of 22 distinct dimensions and their location in all four quadrants applying ordinal medians is truly remarkable. Realistically, there were only a few phenomenological components that were different. In other words, Psychotics were having Associative déjà vu and exhibited no startling profound features other than their key distinct feature and problem adding to this, namely consistent misinterpretation of reality, referential phenomena and delusional and hallucinatory thinking [2,6]. This is well reflected in the analysis of Figure 6C showing the specific dimensional features in the 5 subpopulations.

These Findings Might Pioneer a New Way of Thinking: As Neppe Points Out

The approach used serves as a model for phenomenologically relevant analyses in neuroscience, psychology, psychopathology and parapsychology. This allows standardized, relevant recordings. This also requires development of further appropriate questionnaires to ensure phenomenological homogeneity in further research and meta-analyses [79].

The differentiation of a precognitive SPE and SPE déjà vu is phenomenologically relevant:The SPE déjà vu event is by definition not definitively precognized before the experience. This allows, at times, a distinct differentiation from actualized precognition, though this may be particularly difficult in déjà rêvé when dream residues exist. Experients sometimes perceive their déjà vécu as due to reincarnation, but this may be one of several possible unlikely explanations. Note that the four distinct nosological subtypes may theoretically manifest in all thirty different déjà experiences.

Further research has led to the New Neppe Déjà Vu Questionnaire (NNDVQ-2006). The possibility of using questionnaires such as these over the Internet becomes a cogent one as provisionally done by Funkhouser at http://funkhouser. dreamunit. net/déjà vu/.

Neppe examines the qualitative features resulting from these questionnaires in some detail elsewhere in his books [38,73,93] as well as comment on comparative incidence [94-96]. The updated modified version of the original questionnaires are modified in the final two chapters of the A Second Look book, Questioning the Déjà Vu Questionnaires [47] and The New Neppe Déjà Vu Questionnaire—2006 (NNDVQ) [29]. An application of this phenomenological research is that the methodology to differentiate subtypes of déjà vu (≥4) can be used to continue such analyses, for example, possibly correlating SPE déjà vu occurring in the distinct population of Subjective Paranormal Experients with other kinds of SPE. Such analyses can only be arrived at using detailed phenomenological analyses, though key features can now be differentiated. We know, for example, that other subtypes of déjà vu (TLE, psychotic, associative) are apparently not SPEs.

However, the broader lesson of the Neppe déjà vu phenomenological research is to motivate the importance of the development of the phenomenological school of Consciousness Studies and also of analyzing neurophysiology and neuropathology in the context of symptoms. Effectively, all possible paranormal experiences, whether subjective or objectified in an empirically based research environment, should be analyzed phenomenologically. This application of the temporal lobe and features linked with it, is far broader in neuroscience than just studying déjà vu: In the context of subjective psi experiences, Neppe in 1977 [97] and Palmer and Neppe in 2003 [98,99] applied such work to temporal lobe symptomatology. Neppe also studied SPEs and olfactory hallucinations [100,101]. Applications of this approach using phenomenological analyses in other areas of subjective experience are highly relevant and can even include subjective experiences such as psychiatric symptoms like hallucinations and delusions.

This kind of analysis can be applied not only to spontaneous SPE case analyses, both prospective and retrospective, but it can also be used in Objective psi Experience [OPE], for example, in the experimental research paradigm, when prospective paradigms allow for a more detailed data set.

Phenomenological detailing ensures a methodology of ensuring that data is recorded in as standardized and relevant a way possible. Neppe has suggested an A to Z Axis Classification of such experiences (applying the mnemonic ‘SEATTLE’). He has specifically empirically demonstrated how subtypes of these 26 Axes can be directed to precognizing events, particularly using sub-classifications (‘TICKLES’ and ‘FOLDINGS’) of two specific axes [102].

Déjà vu occurs in about 2/3 of the population. This is predominantly the common kind, namely Associative Déjà Vu in which 23 déjà experiences predominantly occur. These are relatively rare during one’s lifetime, invoke some perplexity but seldom a marked impression and are often rationalized, It differs from the other subtypes described, as such experiences are generally of short duration, relatively unimpressive because they’re not usually intense, nor do they include a precognitive impression, or specific symptom sequences, or aspects of thought disorder.

By far the most pertinent and common type of déjà vu is ‘Associative déjà vu’.

Déjà experiences hypothetically manifest frequently in the normal population: Based on several studies world-wide, across “normal” populations and those with psychiatric or brain illnesses, using several broad screening questions, possibly two-thirds or even 70% of individuals have had at least one déjà vu experience in their lifetime [81], usually ‘Associative déjà vu’. But this associative déjà vu is not specific to the general population and can occur in conjunction with or instead of other kinds of déjà vu experiences in any subtype.

Descriptions of ‘Associative déjà vu’ are most often vague, associated with perplexity (“Now why did this happen? And why now? I can’t really explain it,”). And, then may come the rationalization phase, where indeed, the experient (the person experiencing it) may ‘associate’ their experience with something: The experient might try to explain their déjà vu possibly with one or more of those 72 explanations. Associative déjà vu experiences are generally short-lived (seconds) and do not impact greatly and they may be associated with a mild psychological experience like relief of anxiety.

This most common type of déjà vu experienced by normal, healthy people is what Neppe originally [2] and still does call Associative Déjà Vu because it is ‘associative’ in nature: You see or hear or talk or visit or experience any of the twenty or more déjà experiences that allow associations-linkages-with something. Such happenings become a complex psychodynamic issue, often with anxiety relief and some association that looks like part of a previous occurrence, or reflects an incompletely forgotten memory.

‘Associative déjà vu’ experiences occur possibly only a few times in a person’s lifetime and usually begins when some aspects of a place or situation suddenly feel familiar [2,6]. Sometimes mild stress or anxiety will prompt it. An unusual action or sight may also trigger a vague, unclear impression of déjà vu. The experience usually lasts but seconds and is unassociated with any substantial change in the person’s thinking or emotions-other than that he or she is bewildered by its occurrence.

The trigger in the following case [3] may be an unconscious conflict the informant had with cigarettes and smoking:
“The one I’m describing happened a year ago. I went into a little corner cafeteria to buy cigarettes. I had never been to that particular shop before nor had I ever seen the shopkeeper before. As I was buying it, I felt the shopkeeper and the whole situation were familiar and I had gone through this experience before. This often happens when I buy cigarettes and has occurred in several small cafeterias. ”

A debatable kind of déjà vu experience is induced or mimicked by so-called ‘restricted paramnesias’-this is the process of partial forgetting where vague yet genuine memories are manifesting in the present in a form reminiscent of déjà vu.

Now is this déjà vu? Yes, it is but one of those situations where one has to invoke the definition: Neppe still regards such partial forgetting as déjà vu insofar as the ‘past is undefined’ initially, even if later it becomes defined-“I know why: It reminded me of my visit to the dentist—I couldn’t explain it but now it’s clearer”. And sometimes, if one has a more direct memory, it would not be déjà vu because it is based on direct memories. That may be one reason why some individuals don’t seem to have déjà vu: They remember too well!

A colleague reported the following experience: [3]

“A patient came to see me. I was meeting him for the first time. The immediate impact was that I had met him before. He looked familiar. I even asked him where we had met, but he denied ever meeting me. Then I thought, ‘Possibly not. ’ At that point I remembered a patient whom I had treated 12 years ago. I realized that I must have mistaken one for the other. ”

In this respect, this experience can be classified as anyone or any combination of the following: a distortion of memory, ego-state defense or error in recognition. In this example, the feeling of familiarity would not be true déjà vu if the subject while having the déjà vu experience were able to recall the actual patient from twelve years before. This would be so as the subject would really be experiencing something from his defined past. However, this is not the case here. Initially, he has the perplexity of “where does he come from? Why is he familiar?” Then comes the rational thinking: “I mistook him for a specific person twelve years ago.” We could consider this experience a form of “restricted paramnesia” in that a process of forgetting has occurred and vague yet genuine memories are manifesting in a form reminiscent of déjà vu [103].

What does this all mean? Simply that no single explanation for déjà vu can cover its entire range of effects.
Many déjà experiences are commonly described in ‘Associative Déjà Vu’. In Neppe’s experience over the past three plus decades, the following are the most common:

déjà lu                                      already read
déjà parlé                                already spoken (act of speech)
déjà visité                                already visited [a locality]
déjà rencontré                        already met; specifically relates to interpersonal situation
déjà raconté                           already recounted [already told]
déjà arrivé                               already happened
and of course déjà vu itself as the generic “already seen”.

In Neppe’s experience, the following are less common in “Associative déjà vu”:

déjà entendu                           already heard
déjà éprouvé                           already experienced [already felt]
déjà fait                                   already done
déjà pensé                               already thought
déjà senti                                 already felt, smelled
déjà connu                              already known (personal knowing)
déjà dit                                    already said/spoken (content of speech)
déjà goûté                               already tasted
déjà trouvé                              already found (met)
déjà articulé                           (already articulated) (old unused)
déjà percu                              (already perceived)
déjà passé                               (already passed) (old unused) uncertain where to classify.

Another four déjà vu subtypes can occur but are so rare that it is hard to describe their origins:

1. déjà touché—already touched. This is a physical sensation and completes all the déjà experiences of all physical senses.
2. déjà mangé —already eaten, chewed
3. déjà musique—already heard or played specific music or sung
4. déjà chanté —already sung

But the traditional global term
déjà vu - already seen, still is pertinent.

The common general, associative type of déjà vu occurring in ostensibly normal individuals is less easy to clearly define and describe. It differs from the other subtypes described, in that, on the one hand, such experiences are generally of short duration and while on the other hand, they can be remembered. Associative déjà vu rarely leaves a deep impression because they it is not as intense nor do they include a precognitive impression, or specific symptoms or aspects of thought disorder. In many instances, one might more accurately speak of instances of mistaken identity or experiences that can be traced—easily or with some effort—to a preceding event or impression [104,105].

An all too striking example of the associative déjà vu subtype was provided by Nathaniel Hawthorne, [106] the 19th century American author of The House of Seven Gables. In 1863, he published Our Old Home, a journal of his travels in England. In a chapter entitled ‘Near Oxford’, he related how he explored the ruins of an old castle at Stanton Harcourt. He was particularly struck by an amazing sense of familiarity he felt within the cavernous kitchen of the place. It was only later that he traced his feeling to a letter of Alexander Pope’s, written to the Duke of Buckingham where he described the kitchen of the place he was staying (without naming it) and Hawthorne had read this letter during his studies many years previously (the psychoanalytic aspects of Hawthorne’s experience were treated in a 1945 paper by Zangwill [76]). Halévy in 1907 [53] and Smith in 1913 [107] have reported similar experiences.

Further complications set in when we realize that the various diagnostic subcategories, the multiple explanations and even the déjà vu experiences themselves, aren’t necessarily mutually exclusive: they can overlap. For example, memory may be distorted due to anxiety, thereby causing the person to block the anxieties by making his memories appear to conform to something that never happened. If this sounds a bit complicated, maybe it can be clarified by looking at the many cases in Neppe’s collection: [2,3] Still some of these explanations are mutually exclusive [6].

Some authors such as Brown have focused on associative déjà vu without defining it as such, regarding it simply as déjà vu. This unfortunately over represents the entity. We must be careful not to allow for “like” phenomena to be over generalized and to be compared with other subcategories-“not like” [102].

Now why the term ‘associative’? Neppe called it this for two reasons

1. This (unlike the term ‘normal’) made it non-prejudicial and allowed for the possibility of the entity to occur with other subtypes. We have on many occasions found that patients with TLE still have associative déjà vu instead of or in addition to their TLE déjà vu. Moreover, as indicated, other non-temporal lobe epileptics and patients with non-epileptic temporal lobe dysfunction have been well demonstrated to have associative déjà vu. [2,3,92]
2. The term ‘associative’ implies some kind of association. Every hypothesized mechanism for this associative déjà vu ultimately has some mechanistic association. This may be psychological, psychoanalytic, psychiatric and cerebral or memory related. But each indicates a link with the individual’s interaction with his environment or his psyche or his brain. Moreover, recent work, including that of Brown, Ito, Kusumi [59], Sno and Wolfradt, has demonstrated a link of previous memories at times [58,108-113]. And in the past, the work of Heymans and Banister supported this [21,89,90,113-115]. Thus, there may even be more support for the term.

Why not replace it with ‘general déjà vu’? Firstly, because ‘associative’ has become the standard and so there needs to be cogent reason to replace it. Secondly, because it would imply just that-general-and this does not mean much when one is describing specific qualitative features.

Associative déjà vu still remains a justifiable subtype three plus decades after it was coined.

Several different explanations and mechanisms for Associative déjà vu are addressed. The contribution of Brown and Marsh in evoking déjà vu by distortions of memory or attention following on Banister’s early work on restricted paramnesias and of the theoretical model of redintegration is examined.

• The Brown and Marsh work evoking déjà vu by distortions of memory or attention with the ‘cell-phone theory’ and associated other contributions are put in perspective with the Banister and Zangwill work on restricted paramnesias and the earlier theoretical contribution of ‘redintegration’. However, the importance of the psychodynamics in inducing this ‘associative déjà vu’ is emphasized.
• Sno’s theoretical holographic model might be a promising one of the 72 possible ways to explain déjà vu.
• The infinitesimal lag ideas of Wigan, Heller and Efron imply a hemispheric role and data on brain stimulation of déjà vu remains difficult to interpret.
• The youngest age of children having déjà vu is documented at age 5 years. This is pertinent for developmental cognitive analyses.

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