Multiple Personality Disorder, or MPD, is an extraordinary syndrome in which two or more integrated alter selves co-exist simultaneously in a single body. It appears to have roots in severe child abuse, and is puzzling and painful both for the persons who suffer from it - who are called multiples - and for the therapists who treat it. Yet researchers and expert observers of the field now say that multiple personality may be the basis for a new understanding of the nature of the mind and its elusive relation to body and brain function.

In a multiple, different personalities who sometimes have no awareness of one another alternately control the physical body. The process by which control of the body passes from one personality to another is called switching, and when a multiple's personalities switch so do a variety of other features.

Alter personalities may differ in terms of voice, posture, physiognomy, handedness and - if preliminary research studies are correct - numerous physiological features such as brainwave patterns, immune status, and skin electrical responses. Behavior patterns, reported life history and (subjectively perceived) sex and age also tend to vary. Different personalities have often mastered different physical abilities, interpersonal skills, and intellectual subject areas. Some may even command entirely different languages!

The average number of alter personalities in a multiple is 8 - 13, although super - multiples may have more than 100 alternates.

By studying such changes and the mechanisms responsible for them scientifically, researchers hope to illuminate a host of key topics in psychology, psychiatry, and related fields such as psychosomatic medicine and brain research. Studies of multiple personality are expected to shed new light on such questions as:

• What are the mechanisms of conscious awareness, and how can multiple streams of conscious activity occur in the mind at the same time?
• How do processes occurring outside of phenomenal awareness influence experience or behavior?
• How do mental and emotional factors influence pain perception, immune function, and other psychosomatic processes?
• What are the mechanisms of volition or "executive control" in human consciousness? What are the mechanisms of "downward causation" in patterns of brain activity?
• To what extent are personality traits or abilities such as intelligence, sensitivity or creativity determined by genetic and environmental influences, and to what extent are they consciously or unconsciously "chosen"?

Cases of multiple personality have always fascinated lay audiences, from fictional accounts such as The Strange Case of Dr. Jekyll and Mr. Hyde to contemporary true stories such as Sybil or The Minds of Billy Milligan. They have also intrigues professional observers from the 17th century to the present. Until recently, however, psychiatrists considered MPD to be extremely rare, and understood little of its scope or dynamics. Now, known cases and new knowledge about MPD are growing at a rapid rate.

Based on clinical research encompassing hundreds of multiples, as well as on preliminary findings from controlled research, a broad picture of multiplicity is beginning to emerge.

Presence of Alter Personalities

When a multiple switches it is typically rapid, usually occurring in 1-2 seconds although in some cases slightly more time is required. Switching may be a voluntary or involuntary event, initiated either through conscious willing, in response to an unconscious emotion or a situation which triggers "automatic" switching, or as a result of biochemical changes in the body.

Drs. Corbett Thigpen and Hervey Cleckley reported one of the first contemporary cases of multiple personality in 1954, in The Three Faces of Eve. They described their initial meeting with one of Eve's alters in a way that conveyed the eerie, trance-like quality that switching sometimes has:

The brooding look in her eyes became almost a stare. Eve seemed momentarily dazed. Suddenly her posture began to change. Her body slowly stiffened until she sat rigidly erect. An alien, inexplicable expression came over her face. This was suddenly erased into utter blankness. The lines of her countenance seemed to shift in a barely visible, slow rippling transformation. For a moment there was the impression of something arcane. Closing her eyes, she winced as she put her hands to her temples, pressed hard, and twisted them as if to combat sudden pain. A slight shudder passed over her entire body.

Then the hands lightly dropped. She relaxed easily into an attitude of comfort the physician had never seen before in this patient... In a bright unfamiliar voice that sparkled, the woman said, "Hi, there, Doc!"