Without looking it up, what can you remember from November 5, 2021? Anything? Me neither. Most of us might remember a major holiday or personal milestone, but little more. A person with highly superior autobiographical memory, or HSAM, may rapidly tell you what day of the week it was, what happened in their life, and what was unfolding in the news.
HSAM is a rare memory ability whereby a person can remember nearly all of their life experiences from adolescence onward. This unusual ability has perplexed researchers for two decades. It has now been 20 years since Elizabeth Parker, Larry Cahill and James McGaugh identified the first known case. Although additional cases have continued to emerge over the years, researchers have struggled to determine what distinguishes people with HSAM from everyone else. People with HSAM often perform unremarkably on standard neuropsychological assessments and common laboratory memory tasks. They are also vulnerable to false memory formation and don’t appear to have a general-purpose memory advantage.
Have Researchers Been Looking in the Wrong Place?
Two newly published case reports offer an important clue about what may distinguish people with HSAM.
In the first, my colleagues and I report on a case of a 16-year-old who we confirmed to have HSAM. When we gave her a date, she immediately named the day of the week and began recalling the events of that day. She could describe whether it was a school day, whether she had taken a test, what she and others had worn, what she ate, and what was happening in her region. As in previous case reports of people with HSAM, she did not stand out on standard neuropsychological assessments or laboratory tasks.
However, we decided to examine something that researchers had not looked at before: her involuntary autobiographical memory.
Most research on human memory, including previous research on HSAM, focuses on voluntary retrieval, when we deliberately try to recall a fact, piece of knowledge, or past experience. Yet, previous HSAM case reports have included anecdotal descriptions suggesting that their participant’s exceptional remembering is not deliberate. Instead, it seems to happen automatically.
This led us to wonder whether people with HSAM differ not in voluntary memory but in involuntary autobiographical memory, when personal memories just seemingly spontaneously pop into our mind (like if, while writing a work email, a past vacation moment suddenly pops into mind). Having these is a normal part of human experience, but we wondered whether someone with HSAM might experience them more often than the average person.
So, we administered a questionnaire called the Involuntary Autobiographical Memory Inventory (IAMI) to the person we identified as having HSAM. In our newly published case report, we show that this person scored two standard deviations above the sample mean reported in prior research, indicating an unusually high frequency of involuntary autobiographical memories. We hypothesize that when past experiences repeatedly enter awareness, they may receive a kind of unplanned mental rehearsal, strengthening those memories over time. This repeated, unplanned rehearsal may support memory consolidation, the process through which memories become more stable over time.
Soon after our report appeared, a European research group led by Krystian Barzykowski published a case study of another 16-year-old with HSAM. They used both the IAMI questionnaire and a newly developed laboratory task designed to capture involuntary autobiographical memories as they occurred. During the task, the participant monitored a monotonous set of patterns on a screen and was periodically asked what had been going through his mind, such as daydreams or involuntary autobiographical memories. On both measures, the participant showed a higher-than-average frequency of involuntary remembering.
Together, these two newly published case reports provide an important new clue about what might underlie HSAM.
For 20 years, researchers largely studied whether people with HSAM are better at deliberately retrieving memories. These two cases suggest a different possibility: Perhaps the crucial difference lies in how often memories return on their own. Of course, two cases cannot tell us whether this pattern characterizes everyone with HSAM, or whether frequent involuntary remembering is a cause of the ability, a result of it, or merely associated with it. But the convergence points to a promising question for future research. If that pattern appears in more people with HSAM, the mystery may turn out to be less about an extraordinary ability to search memory for the past and more about a past that repeatedly returns on its own.
