Washington: U.S scientists have discovered intriguing differences in the brains of an extraordinary group of people who can effortlessly recall every moment of their lives from 10 years onwards.

The phenomenon of highly superior 'autobiographical' memory has been profiled on CBS's "60 Minutes" and in hundreds of other media outlets. It was first documented in 2006 by University of California - Irvine (UCI) neurobiologist James McGaugh, who also co-authored the current study, and colleagues.

But a new study offers the first scientific findings in a group of people with this uncanny ability, the journal Neurobiology of Learning & Memory reports.

Surprisingly, the people with stellar autobiographical memory did not score higher on routine lab memory tests or when asked to use rote memory aids. Yet when it came to public or private events that occurred after age 10, "they were remarkably better at recalling the details of their lives," said McGaugh, senior study author, according to a California statement.

"These are not memory experts across the board. They're 180 degrees different from the usual memory champions who can memorise pi to a large degree or other long strings of numbers," said Aurora LePort, doctoral candidate at UCI Centre for the Neurobiology of Learning & Memory, who led the study.

"It makes the project that much more interesting; it really shows we are homing in on a specific form of memory."

LePort said interviewing the subjects was "baffling. You give them a date, and their response is immediate. The day of the week just comes out of their minds; they don't even think about it. They can do this for so many dates, and they're 99 percent accurate. It never gets old."

The study also found statistically significant evidence of obsessive-compulsive tendencies among the group, but the authors do not yet know if or how this aids recollection.

Many of the individuals have large, minutely catalogued collections of some sort, such as magazines, videos, shoes, stamps or postcards.

UCI researchers and staff have assessed more than 500 people who thought they might possess highly superior autobiographical memory and have confirmed 33 to date. Another 37 are strong candidates who will be further tested.

"The next step is that we want to understand the mechanisms behind the memory," LePort said. "Is it just the brain and the way its different structures are communicating? Maybe it's genetic; maybe it's molecular."

McGaugh added: "We're Sherlock Holmeses here. We're searching for clues in a very new area of research."