OCD linked to memory
Some people can remember what they did on a specific day, years ago.Istock

Some individuals are able to remember precisely what they were doing a day, a week or even a year ago. This extraordinary ability to recall past experiences could be due to a unique kind of obsessive-compulsive disorder (OCD), scientists claim.

The first case of "Highly superior autobiographical memory" (HSAM), also known as hyperthymesia, was first documented in 2006. HSAM can be described as the ability to accurately remember an exceptional number of experiences, and the dates on which they occurred, over many years. Less than 100 people in the world have this very particular kind of memory.

In the last decade, many scientists have tried to understand the phenomenon and have examined the brains of those exhibiting the trait to explain the occurrence of HSAM. In two recent studies, they have identified specific cognitive and behavioural mechanisms, shared by people with hyperthymesia.

No superior cognitive skills

A publication in Memory, studied whether people with HSAM displayed particularly advanced cognitive functions, which could explain why they remembered so many things. The research was led by James McGaugh, the neurobiologist who described the first 2006 case. It examined 20 people with HSAM. The subjects were then tested for verbal fluency, ability to memorise patterns and remember people's faces and jobs.

Surprisingly perhaps, the participants' results at the tests were only slightly better than people of the same age, with "normal" memory. "Superior cognitive functioning is an unlikely basis of HSAM, as only modest advantages were found in only a few tests", the scientists concluded.

OCD boosting memory

The scientists also found that the subjects seemed to recall their personal experiences much better than that of others. In a separate study, published in Frontiers in Psychology, they tried to explain the reason behind this.

Thirty volunteers were asked to recall events that occurred each day of the week leading up to the study, as well as a week that happened a month, a year, and a decade earlier. The scientists tested them again later for the same dates, to check if the memories was were consistent. During these experiments, the scientists were able to pinpoint common behavioural patters. They discovered the participants tended to display obsessive behaviour, not unlike people with OCD.

Their results suggest that people with HSAM do not implement any concious strategy to remember things in details. However, their obsessive-compulsive behaviour leads them to constantly reflect on and order memories from their past. This particular form of OCD could thus have the effect of boosting memorisation skills in the long term.