For most of us, our memories are filled with the minutiae of our personal lives. We tend to remember that relatively unimportant time we went to McDonald’s with our grandma for years, while information learned in high school about the U.S. Constitution slips away just months (if we’re being optimistic) after learning it. For people with highly superior autobiographical memory (HSAM), it’s even more dramatic.

People with hyperthymesia, as it’s often called, can remember almost every little thing that happened to them over the course of their lives. They can remember back to things that happened to them in the crib, and can often recall in great detail every single event they've experienced, no matter how minor, from the point when they were 10 or 11 years old. They can remember that the U.S. invaded Iraq on a Wednesday in March 2003. They can probably remember what they had for breakfast that day, too, and whether or not they felt tired. Here are nine things you might not know about the rare condition.

1. IT’S A POPULAR DOCUMENTARY SUBJECT.

Hyperthymesia has been the subject of a 60 Minutes special, a Channel 4 documentary in the UK, and countless newspaper and magazine reports (including our own). In 2010, Brad Williams (a one-time Jeopardy! contestant) became the star of his own documentary, Unforgettable, directed by his brother.

Superior memory is also a popular topic in fiction. The classic example of hyperthymesia in literature may be Jorge Luis Borges’ short story “Funes the Memorius,” in which the main character suffers a head injury that results in the ability to remember everything in exquisite detail. Hyperthymesia has also been featured in young adult books, been a plot point on House, and used to characters’ advantages on crime-solving TV shows like Unforgettable. And yet ...

2. SCIENTISTS HAVEN’T KNOWN ABOUT IT FOR LONG.

The first case was reported in the journal Neurocase in 2006. It described “AJ,” a woman who can recall events and dates from her life with incredible accuracy. Researchers from the University of California, Irvine spent five years interviewing her and testing her abilities before the paper went to press. The patient later revealed herself to be a woman named Jill Price. She published a memoir about her life with hyperthymesia in 2009.  

3. IT’S EXCEEDINGLY RARE.

At this time, there are only a handful of individuals in the world who have ever been diagnosed with hyperthymesia, and scientists still don’t know exactly how it works. Some studies have found that hyperthymesiacs might have variations in the structure of their brains, while others argue that it might have behavioral components. However, since so few people are diagnosed with HSAM, it’s difficult to study the condition.

4. IT’S A SELECTIVE GIFT.

Price, who can instantly recall the day of the week and what she was doing on almost any day going back to when she was 14 years old, told researchers that she couldn’t apply her superior memory skills in school. She reported having “great difficulty with rote memorization,” telling the researchers that “it [meaning her memory] doesn’t work that way. I had to study hard. I’m not a genius.” One day in the lab, researchers asked her to close her eyes and recall what clothes she was wearing that day. She couldn’t remember.

5. IT USUALLY INVOLVES A SUPERIOR MEMORY FOR DATES.

Hyperthymesia involves more than just remembering everything that happened to you; it’s also about remembering exactly when it happened. For instance, Price can label what day of the week virtually any calendar date fell on. Given a specific date, like “March 19, 2003,” a 20-year-old hyperthymesiac called HK can remember that it was a Wednesday, what the weather was like, and what he did that day from getting up to going to bed. When asked how he remembered dates and events so clearly, he told the researcher, “They just come into my mind. I can just picture it as if I was there again. Especially when anniversaries come around. That day of the anniversary, I just think back to what I was doing, what the weather was like, who I was with, and so-and-so. I just remember it.”

6. IT MAKES THE PAST FEEL LIKE THE PRESENT.

HK sees most of his memories happening in the first person, "through his eyes," as he describes it—even though he’s blind—as if it were happening in the present. “I can remember all kinds of facts,” he said. “But when I think about something from the past, an event or something, I fell like I am right back in that situation. There really is no difference in when it happened and when I remember it.”

7. IT MAKES MEMORIES FROM YEARS AGO FEEL EMOTIONALLY INTENSE.

Louise Owen, a hyperthymesiac interviewed by 60 Minutes in 2010, had a strong reaction when the reporter brought up an unhappy day from her past:

Just the mention of a sad day, like the one in 1986 when Owen learned she'd have to change schools, and she relives it emotionally. "I felt like my whole world was collapsing. And you say that and it's like all of a sudden I feel like this really heartbroken little 13-year-old all over again," she explained.

She said the feeling was vivid and awful, even after all these years. "I mean, my heart is actually pounding right now in telling you this," she told [reporter Lesley] Stahl.

8. IT CAN BE A BURDEN AT TIMES.

Owen described some of the darker aspects to her gift to 60 Minutes. "Sometimes, having this sort of extreme memory can be a very isolating sort of thing," she said. "There are times when I feel like I'm fluent in a language that nobody else speaks. Or that I'm walking around and everybody else has amnesia."

And Price, researchers wrote in 2006, “is bound by recollections of her past.” She is constantly reliving moments from her personal history. Some, like cognitive psychologist Gary Marcus, who interviewed Price for WIRED magazine, points out that people with superior autobiographical memory share some traits with people with OCD, like obsessively thinking about dates and events.

9. IT DOESN’T MAKE YOU IMMUNE TO FALSE MEMORIES.

A 2013 article in PNAS indicates that despite their superior recall, people with hyperthymesia are still susceptible to false memories. Hyperthymesiacs were just as suggestible as the control group to incorrectly remembering nonexistent news footage, for instance.