Some experts may find Mr. Oxnam's claims dubious, because psychiatrists are at odds about the condition's very existence. But in any case, "A Fractured Mind" traces a vivid narrative path into the recesses of one man's mind, where a whole world -- literally a castle with rooms, dungeons, walkways, ramparts and a library behind iron-locked doors -- had come into being. The book is written, like some novels, with different first-person narrators, a seeming contradiction for an autobiography. In the end, the search for the awful source of Mr. Oxnam's disturbance emerges almost as an adventure story akin to the archaeological quests of Indiana Jones.

"Archaeology is the right metaphor," Mr. Oxnam said during one of two interviews this week in his apartment on the Upper West Side of Manhattan, one in the company of Dr. Smith, the other with his wife, Veshakha Desai. "Because you're going back in reverse history."

Therapy ultimately uncovered 11 different personalities inhabiting the castle of Mr. Oxnam's psyche, including Baby, who revealed what seems to have been long and habitual abuse of Mr. Oxnam as a toddler. Each had a name and identifiable qualities, a community of the shy and the obstreperous, the diligent and the indulgent, the cruel and the kind, the athletic and the retiring, the erudite and the hopelessly uninformed.

"It can get really noisy in there, a din," Mr. Oxnam said, adding that a particular type of headache accompanies the inner clamor.

Now 62 and working as an independent consultant on China, Mr. Oxnam is a soft-spoken man, tall and bearded, a hearty physical specimen who still looks weary and a little haunted in the eyes. The noise inside is somewhat reduced these days. Therapy has, in the lexicon of psychiatry, merged many of his personalities -- three remain active -- and in conversation he includes them, speaking of "we" as often as "I." Writing the book, he said, was a group effort, with one of his personalities writing a chapter and the rest examining it.