01 April 2000
DÉJÀ VU — A TOUCH OF TEMPORAL LOBE EPILEPSY?
There are certain run-of-the-mill experiences that give all of us a little taste of what it might be like to have a brain disorder. Dreams are one example. Another is what is called déjà vu (literally, "already seen") — a short-lived, overwhelming, but false sense of having already lived through the present moment, and of being able to predict what is about to happen next.
Some psychologists and neurologists have referred to the uncanny feeling that accompanies déjà vu as a doubling of consciousness: simultaneous sensations of familiarity and strangeness, a momentary conviction of having experienced something before coupled with a recognition of the impossibility of having done so. So déjà vu is the type of experience that makes us aware that even a "normal" brain less is seamlessly unified than we sometimes think.
Déjà vu is, in some ways, like a mild version of a disorder known as confabulation. Confabulators may quite honestly come up with outlandish responses to simple questions — for example, "I take orders from Joseph Stalin — you thought he was dead? — through this chip implanted in my left ear," in response to, "What do you do for a living?" Confabulation can result from frontal lobe injury or organic brain disease, such as Alzheimer's, or from a mental illness such as schizophrenia.
Déjà vu is essentially the opposite of something called jamais vu (literally "never seen") — a false sensation that a familiar situation or experience is strangely unfamiliar. Jamais vu can be associated with epilepsy or schizophrenia.
Two things about déjà vu that make it a "normal" experience rather than a disorder are its ubiquity — about 96% of all people have it — and the fact that it doesn't interfere with normal functioning. The important factor is that, unlike confabulation, a déjà vu "memory" is brief and isn't really confused with reality. On the other hand, there is something called a "major form" of déjà vu in which the eerie sensation of having already lived through a novel experience lasts longer, and may be permanently incorporated into a new, false version of reality. The major form of déjà vu can be a symptom of schizophrenia, a mood disorder such as bipolar disorder (manic depression), or an organic brain disorder such as temporal lobe epilepsy.
What's going on in the brain to cause déjà vu? One theory proposes an explanation in terms of a timing problem between the brain's left and right hemispheres. By this view, each hemisphere perceives events and records information independently of the other, but constant instantaneous communication between the brain's two sides gives us the illusion of unity. If, however, there is a brief delay in transmission from the "non-dominant" (usually right) to the "dominant" (usually left) hemisphere, the dominant side receives the same information twice, once directly and once after a brief delay from the opposite half of the brain.
Some psychologists have attributed déjà vu to a memory of a dream. Even though this theory is not taken very seriously by most brain scientists, there does appear to exist some intriguing evidence of a connection between dreams and déjà vu. In a study of 58 of his patients, one psychotherapist found that ten who claimed not to dream also claimed never to have had a déjà vu experience.
Research on the brain basis of temporal lobe epilepsy has yielded insight into a likely anatomical origin of at least some instances of déjà vu. Neuroscientists such as Wilder Penfield have known for decades that a "dreamy state" — vivid memory-like hallucinations and a déjà vu-like sense of having already lived through the present moment — can be evoked through electrical stimulation of an area of the temporal lobe in a fully conscious epileptic patient under local anesthesia.
Other more recent experiments using EEG recordings show that stimulating the temporal lobe, hippocampus, or amygdala can trigger a déjà vu experience involving all three regions. Imaging studies also show that this is the same network of brain areas involved in a temporal lobe epileptic seizure. The hippocampus and amygdala are brain structures crucially involved in memory and emotion. The involvement of the hippocampus and amygdala in déjà vu may explain the mélange of memory-like sensations and emotional components that déjà vu combines.
This evidence indicates that the déjà vu experience is, in a sense, like a small, brief epileptic attack that fails to spread to as many regions of the brain, and thus fails to trigger a full-blown epileptic seizure.
This puts almost all of us into the company of such notable temporal lobe epileptics as Dostoevsky, van Gogh, and Rasputin. According to some researchers, Joan of Arc (who, before being burned at the stake, claimed that God instructed her to save France from the English) and the Old Testament figure Abraham (who supposedly heard God tell him to kill his son Isaac) may also have suffered from auditory hallucinations resulting from temporal lobe epilepsy.
|
