A small group of people who can remember what happened to them on just about any day during their lifetimes have fundamentally different brains, UC Irvine researchers have found.

Using brain MRIs, and various behavioral and memory tests, researchers examined 11 people with what is known as highly superior autobiographical memory, or HSAM.

Those 11 were confirmed among a pool of 115 who claimed to have HSAM, according to the study published in last month's journal Neurobiology of Learning and Memory.

Those with HSAM are able to recall immense amounts of information, including dates and experiences from throughout their lifetimes.

This is an exceedingly rare trait, according to the study's lead author, Aurora LePort.

Among those with the superior memory is actress Marilu Henner, who starred in the 1970s TV series "Taxi."

In their testing, UCI researchers found that those with HSAM have far more white matter connecting gray matter, which creates better communication within a region of the brain, LePort said.

Gray matter is akin to the buildings in a city, while white matter is similar to the roads between each building, she said.

Tests showed an increase in white matter in five of nine regions of the brain, the study reported. It also found that six regions of those with HSAM differ in size and shape.

While those with HSAM can remember a personal event, they are not more capable at memorizing a grocery list, remembering which key goes to which door or recalling a long string of numbers, like people who memorize pi.

Unlike some autistic savants who can think of a date and day of the week dating back centuries, those with HSAM are limited to remembering events within their lifetime. The also do no exhibit some of the side effects of autism, which can include difficulty making eye contact, according to the study.

Memories of dates and experiences typically aren't intrusive or disruptive in the day-to-day lives of most of those with HSAM, the study found.

Those with HSAM have a higher tendency toward obsessive behavior and recurrent thoughts, the study found.

Nine of the 11 HSAM people reported that they hoarded, and some obsessively avoided germs.

In a 2010 "60 Minutes" segment on superior memory, Henner took the show's host, Lesley Stahl, to her closet, where she recalled when and where she first wore every pair of shoes that were neatly lined on the shelves.

Researchers next hope to examine whether the trait is genetic, how memories are encoded and examine whether those with HSAM take in information differently than those without it, LePort said.

"I think it has a lot of implications for understanding memory," LePort said. "Usually you study memory from a deficit [perspective] … This gives us a way to study memory when it's working at a high level."

lauren.williams@latimes.com

Twitter: @lawilliams30