The People Who Can Perfectly Remember Every Single Day of Their Lives

We all have moments when our memory fails us. It gets to Monday morning and we can't tell a coworker where we were Friday night, or we're at a pub trivia night and for whatever reason we struggle pathetically to remember the name of the lead singer from the Cure. However, for better or for worse, remembering stuff isn't a problem for those with highly superior autobiographical memory (HSAM).

HSAM—or hyperthymesia, as it's also known—is characterized by the ability to remember almost every day of your life after the age of ten or 11 years old, down to the most minute detail. When given any past date, people with HSAM can usually recall things like what color dress they were wearing, or even what the weather was like. It's unknown whether people are born with HSAM or develop the ability in their early years. So far, 61 people in the world have been identified as having HSAM, including 56 in America and five in the UK.

I asked Joey DeGrandis, a 30-year-old New Yorker with HSAM, to recall what he did on July 9, 1995. He answered down the phone without hesitation: "July 9, 1995—it was a Sunday—I was in Chicago with my family for vacation and I believe we went to Shedd Aquarium that day. Another random memory: I remember watching I Love Lucy a few days later at my friend James's house on Tuesday, July 11; it was an episode where Lucy and Ethel were crying at the end… but it was 'funny' crying."

The date I gave Joey is my birthday, and I can barely remember what I did last year for it, so how on earth did Joey recall what he was apparently doing with such clarity?

Joey tells me that the way he retains and absorbs memory is very chronological: "The best way I can describe it is that I view my life like a movie. It's almost like when you go to a DVD and you're scrolling through the different chapter scenes. When I'm thinking about my life, I hone in on a time and access it like you would a chapter of a DVD."

James McGaugh, at the University of California, Irvine, was the first to discover this phenomenon in 2006, with a woman who identified herself as "AJ." McGaugh has now identified 56 people with HSAM out of hundreds tested. Aurora LePort, a doctoral candidate at UCI's Center for the Neurobiology of Learning and Memory, described the condition in a 2012 press release as "baffling." She wrote, "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."

It sounds like the kind of skill that could be a pretty handy tool in life, but people with HSAM aren't, for example, any better at exams; their ability lies in accessing a very specific type of memory relating to their life and experiences. There is still much to be discovered about why this is. In that 2012 release about HSAM, McGaugh said, "We're like Sherlock Holmeses here. We're searching for clues in a very new area of research."

Memory expert Professor Giuliana Mazzoni, from the UK's University of Hull, told me that hearing about HSAM was a "feast for the ears of a memory researcher." When she heard of the phenomenon being discovered in the US, she set out to try to find cases in the UK. Of the 200 people that got back to her, she is certain that five of these have HSAM.

Mazzoni uses a number of methods to check that her subjects aren't just making it up. One method is by asking them facts like, "What was shown on TV that day?" or "How was the weather?" People more interested in sports were able to remember games and teams and scores, people more tuned into TV were able to remember TV shows. She also uses a method called "test re-test," taking a sub-group of dates and asking for recall of these after two months, four months, and so on. This was then compared to the content of another sub-set of dates. Mazzoni was amazed by the accuracy of the results. "They could remember seemingly trivial things, and they could remember them reliably over time, which was amazing."

So was there anything really different about these people's brains, which could back up Mazzoni's observations? Astoundingly, no. Mazzoni found no real difference in the structure of the brain. The difference was found not in the structure but in the order of how the brain works, in the areas of the brain that kick in first, second, and so on.

Mazzoni's working hypothesis is that in these people, episodic memories—that is, contextual memories of autobiographical events—become, to a certain extent, facts. These people exploit their semantic skills, their ability to process ideas and concepts that are not drawn from personal experience, and as a result have an excellent episodic memory. "The date is associated with a number of events, which are linked very strongly and immediately retrieved in response to the date. They are retrieved as pre-packaged facts."

Mazzoni told me how having such an unusual memory could translate in social situations. "People with HSAM are to a certain extent used by others as repositories of memories." They suddenly become the textbook for everyone's past, typically being asked if they remember this or that day, what they did, and so on. Mazzoni acknowledged, "That can wear relationships out because you are put in a certain role. You are seen as a little different, and being seen as different, even if with a superior skill, is not necessarily that easy or that welcome."

When I spoke to Joey, he expressed a similar opinion: "Sometimes I try to gloss over it and just say, 'Oh, yeah, I just have a crazy good memory,' but it does often require that I go into it because nine times out of ten people are amazed. Then it's sort of just like a windfall from there: 'Do my birthday!' or 'What's this date?' It becomes like a little game. When it comes up in conversation it has a way of taking over the conversation." Sounds a bit like when you dye your hair, or break a leg, when you're forced to explain or retell your anecdote to every person you encounter: a useful conversation starter, but a repetitive one nonetheless.

When Joey took part in the study on HSAM at the University of California in 2014, he had the opportunity to meet others with HSAM, which he described as "refreshing."

"For one, we didn't have to explain every time we threw out a date," he said. "In normal conversation we usually get a double-take—'How did you know that?'—but with this, the conversation just flowed. We found that we had similarities in terms of our memories and the way that we process things. It was nice to bond in that way."

Many of the people Joey met with HSAM found it difficult to forget bad memories, particularly due to the strong emotional content they retrieved. "Whatever's important to me, whatever I do absorb, it really sticks. The good and the bad: If I'm remembering or recalling a memory, I'm almost reliving it emotionally as well. I'm back in that place in time. It's like time travel." In this way, Joey said that the emotions of his past could be quite overwhelming; they are not left in the past but sustain into the present. "It's bad for relationships because you can think of all the things that went wrong," he says. "It's self-analyzing in the worst way, it's almost like your mind is your own worst enemy."

I asked Mazzoni if she would like to have that sort of superior memory. She wasn't sure. "I have mixed feelings because I think, on one hand it could really enrich my life—remembering all the things that had happened to me would be wonderful. On the other hand, it might also become problematic—in the sense that with the good things you remember the bad things and bad experiences occur relatively often in life and so you might decide that you had more bad experiences than good and start having a negative attitude."

Despite the practical and more sentimental benefits of HSAM, it is undoubtedly a double-edged sword. I asked Joey whether he would want to remove the ability if he could. "Even though sometimes the bad memories may haunt me, I think that overall I'm happy to have the ability."

Follow Amber on Twitter.