People with hyperthymesia (also called highly superior autobiographical memory, or HSAM) are able to remember events from their lives with an incredibly high level of detail. Given a random date, a person who has hyperthymesia will usually be able to tell you what day of the week it was, something they did that day, and whether any famous events happened on that date. In fact, in one study, people with hyperthymesia were able to recall what they had been doing on specific dates even when they were quizzed about days 10 years in the past. Nima Veiseh, who has hyperthymesia, describes his experiences to BBC Future: “My memory is like a library of VHS tapes, walk-throughs of every day of my life from waking to sleeping.” The ability that people with hyperthymesia have seems to be specific to remembering events from their own lives. People with hyperthymesia generally can’t answer these same types of questions about historical events that happened before they were born, or about memories from earlier in their lives (their extraordinary memory typically starts around their preteen or early teen years). Additionally, researchers have found that they don’t always do better than average on tests that measure types of memory other than memory of their own lives (such as tests asking them to remember pairs of words given to them in a research study).