At the most fundamental level, experiential symptoms are illusions or hallucinations that result in erroneous interpretations of the present experience. Frequent types of experiential symptoms include sensations of déjà-vu or jamais-vu, episodes of disorienting hyperfamiliarity, and a variety of out-of-body experiences termed “autoscopy.” If epileptic in origin, experiential symptoms occur almost exclusively in temporal lobe epilepsy.
Experiential phenomena can occur in healthy individuals, in the context of psychiatric disease, or during the aura phase of migraine headache and have been associated with mass lesions or inflammatory conditions of the temporal lobe.
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• Experiential symptoms are illusions or hallucinations that result in erroneous interpretations of the present experience.
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• Frequent types of experiential symptoms include déjà-vu, jamais-vu, hyperfamiliarity, and out-of-body experiences termed “autoscopy.”
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• Seizures with experiential symptoms are most frequently symptoms of focal epilepsy arising from the temporal lobe, most likely the mesial structures.
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• Similar phenomena can occur in patients with no neurologic disease, in the context of psychiatric disease, or during the aura phase of migraine headache and have been associated with mass lesions or inflammatory conditions of the temporal lobe.
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• Déjà-vu and jamais-vu may also occur in healthy people.
Historical note and terminology
Hughlings Jackson compiled the first study of experiential seizures in 1891 and called them “dreamy states” (27). He described patients with epileptic convulsions who experienced episodes of “dreams mixing up with present thoughts.” In the 1950s and 1960s, Wilder Penfield, working at the Montreal Neurological Institute, described patients who experienced vivid memories during electrical stimulation of the lateral temporal lobe (41). Penfield called them “experiential phenomena” because they had a “compelling immediacy similar to or sometimes more vivid than the patient’s recall of his or her own past experiences.” In the 1990s, Jean Bancaud studied experiential symptoms induced by seizures using intracranial electrocorticography and found that experiential phenomena occurred during ictal activation of the mesial temporal structures (04). In 2007, Jean-Pierre Vignal confirmed their findings likewise using intracranial EEG. In 2010, the ILAE Commission on Classification and Terminology classified experiential symptoms as “focal seizures involving subjective sensory or psychic phenomena only” (08). The 2017 operational classification of seizure types by the ILAE replaced the term “psychic” with “cognitive” (22; 21). A cognitive seizure also includes positive cognitive phenomena such as déjà vu, jamais vu, illusions, or hallucinations (22). This new classification also introduced the term awareness, which is defined as knowledge and understanding that something is happening or exists. If awareness is impaired for any portion of the seizure, then the seizure is classified as a focal seizure with impaired awareness (22; 21). A focal aware seizure replaces the previously termed simple partial seizure and a focal impaired awareness seizure replaces the term complex partial seizure (22; 38). Therefore, according to this new operational classification, experiential seizures are defined as focal aware cognitive seizures (22; 21).
Symptoms experienced during epileptic seizure are closely related to the region of the brain where the seizure originated. For example, if a seizure arises from the primary auditory cortex of the temporal lobe, the patient commonly perceives elementary sounds. In this instance, the patient experiences an alteration in a single sensory modality, ie, hearing. If a seizure arises from regions involved in integration of sensation, emotion, and memory, the patient may experience a much more complex alteration of their mental state. For instance, seizures that originate from the temporal lobe may cause the patient to feel a false sense of familiarity and generate the illusion that the patient is reliving a past event. Such complex disruptions in conscious experience have gone by many names, including experiential symptoms, psychical auras, and dreamy states. Symptoms designated as experiential include vivid memories, episodes of hyperfamiliarity or unfamiliarity, states of depersonalization, out-of-body experiences, feeling that someone is nearby, and multiple types of emotions such as fear, pleasure, and sadness (Williams et al 1956; Daly et al 1958; Strauss et al 1959; Weil et al 1959; 19).
Seizures with experiential symptoms have common features. Firstly, at the most basic level, all experiential symptoms are illusions or hallucinations that result in erroneous interpretations of the present experience. The stream of consciousness is mislabeled and contaminated by remote memories and false emotions. Secondly, experiential symptoms result from faulty association between perception, memory, and effect (25). For example, a patient may report feeling good because the room feels familiar, like something from their past. Thirdly, the experiential seizures commonly produce a disruption in multiple sensory modalities. For instance, a patient reports seeing and hearing falsely familiar experiences. Lastly, seizures with experiential symptoms usually do not produce loss of awareness or inability of interaction. They produce an alteration in the content, but not in the level of conscious experience.