March 20, 2006 -- -- James McGaugh is one of the world's leading experts on how the human memory system works. But these days, he admits he's stumped.

McGaugh's journey through an intellectual purgatory began six years ago when a woman now known only as AJ wrote him a letter detailing her astonishing ability to remember with remarkable clarity even trivial events that happened decades ago.

Give her any date, she said, and she could recall the day of the week, usually what the weather was like on that day, personal details of her life at that time, and major news events that occurred on that date.

Like any good scientist, McGaugh was initially skeptical. But not anymore.

"This is real," he says.

Soon after AJ took over his life, McGaugh teamed with two fellow researchers at the University of California at Irvine. Elizabeth Parker, a clinical professor of psychiatry and neurology (and lead author of a report on the research in the current issue of the journal Neurocase), and Larry Cahill, an associate professor of neurobiology and behavior, have joined McGaugh in putting AJ through an exhaustive series of interviews and psychological tests. But they aren't a lot closer today to understanding her amazing ability than they were when they started.

"We are trying to find out, but we haven't hit 'bingo' yet," says McGaugh.

His initial hypothesis, like several others, has turned out to be wrong -- or at least incomplete.

McGaugh has spent decades studying how such things as stress hormones and emotions affect memory, and at first he thought AJ's memories were of such emotional power that she couldn't forget them.

But that hypothesis fell short of the mark when it became obvious that "the woman who can't forget" remembers trivial details as clearly as major events. Asked what happened on Aug 16, 1977, she knew that Elvis Presley had died, but she also knew that a California tax initiative passed on June 6 of the following year, and a plane crashed in Chicago on May 25 of the next year, and so forth. Some may have had a personal meaning for her, but some did not.

"Here's a woman who has very strong memories, but she has very strong memories of things for which I have no memory at all," McGaugh says.

That became particularly clear one day when he asked her out of the blue if she knew who Bing Crosby was.

"I wasn't sure she would know, because she's 40 and wasn't of the Bing Crosby era," he says.

But she did.

"Do you know where he died?" McGaugh asked.

"Oh yes, he died on a golf course in Spain," she answered, and provided the day of the week and the date when the crooner died.

When the researchers asked her to list the dates when they had interviewed her, she "just reeled them off, bang, bang, bang."

She also told McGaugh that on the day after a particular interview, which took place several years ago, he flew to Germany.

"I said what? I went to Germany? I couldn't even remember what year I had gone to Germany," he says.

That level of recall suggests another hypothesis. Some people are able to recall past events by categorizing them. Certain events, or facts, are associated with others, and filed away together so that they may be easier to access. That's a trick that is often used by entertainers who use feats of memory to wow their audience.

AJ does have "some sort of compulsive tendencies. She wants order in her life," McGaugh says. "As a child, she would get upset if her mother changed anything in her room because she had a place for everything and wanted everything in its place.

"So she does categorize events by the date, but that doesn't explain why she remembers it."

Also, her degree of recall is so much greater than any other person's in the scientific literature that it seems unlikely to be the complete answer, McGaugh adds.

She is also quite different from savants who have surfaced from time to time with extraordinary abilities in music, art or memory.

"Some of them can remember every single detail about the particular hobby that they have, such as baseball or calendars or art, but they are very narrow," he says. McGaugh described one person who could memorize a piece of music instantly, and not forget it, but who "couldn't make change or couldn't take a bus because he didn't know where he was."

By contrast, AJ is a " fully functioning person," McGaugh says.

The researchers are preparing to take their work in a new direction in hopes of understanding what is going on here. It's possible AJ's brain is wired differently, and that may show up through magnetic resonance imaging. Testing is expected to begin within six months.

"We will be looking at her brain, using brain scanning techniques, to see if there's anything that is dramatically different that we can point to," McGaugh says.

Those of us with normal, very fallible memories function somewhat like a computer in that different areas of our brains are interconnected and thus better-suited for general memories. We know where we live and how to get to work, but we may not know what the weather was like on this date four years ago.

It's possible that AJ's brain has some "disconnections" that help her recall past events from her memory bank without interference from the parts of her brain that act as general processors. But the problem is that even if they find some interesting wiring through brain scans, the researchers will be limited in their conclusions by the fact that AJ seems to be unique.

So unique, in fact, that the Irvine team has given her condition a new name. They call it hyperthymestic syndrome, based on the Greek word thymesis for "remembering" and hyper, meaning "more than normal."

Some day, the researchers say, they hope to know what's different about AJ's brain, but they are still a ways off.

"In order to explain a phenomenon you have to first understand the phenomenon," McGaugh says. "We're at the beginning."