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."