Enhanced semantic memory in a case of highly superior autobiographical memory

Highly superior autobiographical memory (HSAM) is characterised by the ability to recall personal events, dates, and news events from long-term memory with profound detail and accuracy. Anecdotes from these individuals suggest that retrieval of rich autobiographical detail is automatic, and often intrusive rather than effortful. We created two novel experiments to objectively verify whether retrieval of information reflects serial or parallel processing in a case of HSAM (R.S.), who has a self-reported superior memory for two sources of personally relevant information: (a) the ability to name days of the week for any given calendar date since the year 2000; and (b) the ability to remember the entire text, practically word-for-word, of the seven Harry Potter books. RS and 10 age-matched controls, who were also aficionados of the Harry Potter series, were presented with pairs of calendar dates or sentences and asked, "Which date came earlier in the week?" or "Which sentence came earlier in the book?" Items within a pair varied in the proximity to one another in time. RS correctly identified earlier calendar dates and sentences with near perfect accuracy, and her reaction time was not impacted by the temporal distance between items. Controls were unable to identify earlier calendar dates and their accuracy and reaction time was dependent on the temporal distance of items. Structural magnetic resonance imaging (MRI) comparing RS with a normative dataset found no significant differences in any memory-related brain regions. Our findings suggest that HSAM memory retrieval for stored information largely reflects parallel processing, rather than a temporal-based system. We also discovered that RS has superior memory for semantic information, boosted by reportedly attaching autobiographical memories to these details. This unusual HSAM phenomenon may hold further clues to creating strong and lasting memories, which appear to be uniquely rich in detail.