There was one more coincidence that the young man wasn’t aware of Kohn happened to be something of an authority on the phenomenon of the “already seen”–better known as deja vu. Intrigued by the mystery, he had begun compiling literary references to the subject when he was in high school, wrote his senior thesis on it in medical school and then became a dermatologist–leaving the solution to others.
But Kohn can take heart. While descriptions of the deja vu experience go back at least as far as Saint Augustine, nobody yet has come up with a definitive theory of what causes it. Explanations to date have included everything from reincarnation, a notion favored by 19th-century Romantic poets, to the modern biological view that it is a disturbance of the temporal lobe of the brain. South African neuropsychiatrist Vernon Neppe, author of a book on the subject, put the number of existing theories at 44, and has since added one or two more. Now a couple of Dutch psychiatrists at the Academic Medical Center in Amsterdam have pitched in yet another, derived from one of the newer-fangled notions about memory itself.
Writing in the December American Journal of Psychiatry, Drs. Herman Sno and Don Linszen contend that deja vu is really a false memory, triggered by a current experience that has some features in common with an earlier one. That idea has been around for a while, but Sno and Linszen base their new wrinkle on the theory, put forth in recent years, that memories are stored in the brain in the form of holograms. The holography principle, used in three-dimensional photography, is that any part of a photographic plate has enough information stored in it to reproduce the whole picture. As a model for brain function, it helps explain how memories can be revived by stimulating a section of the brain and, at the same time, why the memory remains even after that section is surgically removed. The implication is that, just as in a hologram, there is enough information tucked into any one cluster of brain cells to evoke an entire memory.
However, say the two psychiatrists, what happens in deja vu is that while clusters of holographic data may comprise totally different memories, portions of them may be identical, momentarily fooling us into thinking we are re-experiencing something. Sno says he found a way to illustrate that hypothesis when he saw a picture of Abraham Lincoln in a Dutch newspaper that reminded him of a photo of Sigmund Freud. By putting the two side by side, first in a scrambled form, then gradually bringing them into sharper focus that reveals them to be two different people, Sno was able to provide an arresting photographic analogy of deja vu.
The theory will have to be proved by more than analogy, of course. Meanwhile, Sno is planning a study using firsthand accounts of deja vu experiences. “Everyone tends to associate this with the question of has there been a previous life,” he says. “For me it’s mystical, and seems an intriguing starting point to study the process of memory storage.”
For decades, researchers have believed that deja vu is usually a false memory–a kind of sleight of hand of the brain by which a few familiar features trick us into thinking we are reliving a past experience. Freud characteristically expressed the phenomenon in terms of conscious and unconscious. A repressed memory, he said, can prompt a feeling of deja vu when something in a conscious experience merely touches on it. More recently, psychoanalysts have pondered why the feeling occurs at a given moment. The going theory is that it comes mostly at moments of anxiety, for example, in an unfamiliar social situation, where it serves to reassure: “I’ve been through this before and I got through it all right; I can handle it.”
Kohn, now on the faculty of the Yale University medical school, recalls–really recalls, that is–having precisely that feeling during his last deja vu episode. It came a few weeks ago, as he contemplated a sea of mostly unfamiliar faces at an American Academy of Dermatology reception in Atlanta. Suddenly, he says, he felt as if he had been through it before, and that helped him relax and enjoy the occasion. The experience, his first deja vu in eight months, didn’t give him quite the frisson he used to get when he was younger and more susceptible to the seemingly otherworldly. “But if anyone was watching me closely,” he says, “they might have detected a slight smile on my face.”
