Study Links Rare Memory Condition to Frequent Involuntary Recall of Past Experiences

Ask a young woman who lives near Atlanta about November 5, 2021, and she can tell you what day of the week it was, what she was wearing, which local parade took place, and how striking the sunset was that evening. She can do the same for many other seemingly random dates across her life. It is not a memorization trick. She has an extremely rare condition called Highly Superior Autobiographical Memory, or HSAM, which lets a person recall nearly all of their past personal experiences in vivid detail.

She is the anonymous subject of a case report published in the journal Neurocase, led by Professor Anne Cleary of Colorado State University. The researchers say the findings add to a basic understanding of how memories are formed and then retrieved, with implications for medical procedures such as brain surgery and for understanding memory changes 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 it worldwide. The best known is probably the actress Marilu Henner, recognized for her role in the sitcom Taxi. Finding such people is hard, because they tend to look average on traditional memory tests and in everyday recall. They excel at autobiographical detail, but on a task like memorizing a list of words they are usually only average.

Cleary offers another reason they may go unnoticed: many standard assessments measure only voluntary retrieval, when a person deliberately tries to remember something. The new report suggests that people with HSAM have more involuntary memories, the kind that surface without effort, often seemingly out of nowhere or while the person is doing something else. Testing of the study subject confirmed that she 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. She added that researchers have long speculated that people with HSAM are better at deliberately retrieving memories, but that this work points instead to how often memories return on their own.

In ordinary circumstances, Cleary said, a lack of spontaneous memories would be a red flag for concerning changes in memory, cognition and brain health. She sees the subject as a chance to study spontaneous memory further and to begin building better neuropsychological assessments, which could be useful across many healthcare settings.

One example is surgery for epilepsy that does not respond to medication. Patients take memory assessments before and after treatment to measure change. Some leave surgery with no memory deficit at all, while others pass the standard tests even though their families report that something is missing. Cleary said this suggests current evaluations may be missing important aspects of memory. To build better tools, she said, researchers first need to know what is mechanistically unique in people with HSAM, who sit at one extreme compared with the public on phenomena such as déjà vu and basic recall tasks.

Daniel Drane, a neuroscientist who studies cognition in epilepsy surgery, is a co-author. His laboratory at Emory University hosted Cleary for the initial testing. Drane has since become the Gerlach Family Endowed Chair of Epilepsy Research at The Ohio State University, where he is setting up a virtual reality and biometric assessment laboratory meant to bridge the assessment gap the team describes. He said he and Cleary assessed the woman together and interviewed her family. She completed standard neuropsychological testing, and recently had a brain MRI and some experimental tasks, which he hopes will feed future work with the Colorado State team and others.

The woman wishes to remain anonymous for now. Cleary said her young age may open further research avenues, particularly on diseases like Alzheimer's that affect memory with age and appear to be related to spontaneous memory formation. The team also wants better ways to identify people with HSAM, including verifiable questions that are neutral across age and native language.