Without looking back at an appointment calendar, diary or searching Google, what can you recall about the day of Nov. 5, 2021? Unless that date happens to hold an anniversary or other special meaning, probably not too much.
But if you ask one young woman living near Atlanta, she can easily name that day of the week and rattle off what she was wearing, the local parade that happened that day, and how impressive the sunset was that evening. Her ability doesn't come from a memory-building parlor trick, and it can be displayed for any number of other seemingly random dates across her life. Instead, the ability stems from an incredibly rare condition known as Highly Superior Autobiographical Memory, or HSAM – the ability to recollect nearly all of one's past personal experiences in vivid detail.
She is the anonymous subject of a recent case report published in Neurocase that was led by Professor Anne Cleary at Colorado State University . Findings support a better foundational understanding of how memories are made and then retrieved, with broad implications for medical procedures such as brain surgery and understanding of changes to memory late in life from diseases like Alzheimer's.
HSAM was first diagnosed 20 years ago. Experts think there may be as few as 100 people with the condition worldwide, with the most famous likely being actress Marilu Henner, best known for her role in the television sitcom Taxi. However, identifying them has proven challenging because they tend to be average at traditional memory testing or memory recollection in everyday life. While they excel at recalling autobiographical details, they are usually only average when it comes to memorizing a list of words, for example.
Cleary said another reason these individuals may go unnoticed is that many standard assessments focus only on voluntary memory retrieval – when we deliberately try to recall something from memory. The new report by Cleary and colleagues suggests that people with HSAM have more involuntary memories, or those that pop into the mind without effort, often seemingly spontaneously or while doing other tasks.
Testing with the study subject confirmed that they experienced involuntary memories far more often than average.
"It seems as if people with HSAM are reliving these past experiences more frequently and that strengthens the memories overall, making memories more stable over time for them," Cleary said. "For years researchers have speculated that people with HSAM may be better at deliberately retrieving memories, but our work seems to show the crucial difference lies in how often memories return on their own, which unlocks a lot of potential avenues for study."
In normal situations, a lack of spontaneous memories would be a red flag for potentially concerning changes to memory, cognition and brain health. Cleary said the study subject represents a unique opportunity to explore spontaneous memory further and begin to develop better neuropsychological assessments to understand what is really going on in the brain when people recollect information. Those new tests could be valuable across any number of healthcare treatment settings.
One example, Cleary said, is people who undergo brain surgery to treat epilepsy that is not responding to medication. Those patients participate in pre- and post-treatment assessments of their memory to measure changes. Some come out of surgery and do not have a memory deficit at all, while others may pass standard tests, but their families still report there is something lacking.
Cleary said that shows current evaluations may not be capturing important aspects of memory.
"We may not have the right assessments in place to fully capture what is going on or to make useful comparisons that would help us learn more about healthy brain functions related to memory," she said. "To develop those tools, we first need to know what is mechanistically unique in people with HSAM who are at one extreme end compared to the broader public when it comes to different phenomena like déjà vu or when performing basic recall tasks."
Daniel Drane is a neuroscientist who studies cognition in the setting of epilepsy surgery and a co-author on the case report. Drane's laboratory at Emory University hosted Cleary for the initial testing of the subject. Since then, Drane has become the Gerlach Family Endowed Chair of Epilepsy Research at The Ohio State University. He is establishing a virtual reality and biometric assessment laboratory to bridge the assessment gap reported by Cleary and colleagues.
"We assessed the young woman together and interviewed her family as well," he said. "She underwent standard neuropsychological testing and also recently completed an MRI of the brain and some other experimental tasks which will be the subject of future work I hope to collaborate on with the CSU team and others involved in this project."
Cleary said the study subject wishes to remain anonymous for now. Her young age may provide other interesting avenues of research, particularly into diseases like Alzheimer's that can impact memory as we age and seem to be related to spontaneous memory formation.
"We also want to develop new approaches to better identify people with HSAM wherever they are. Part of that is developing verifiable questions that are also neutral for demographic differences like age or native language," she said.
