Stimulating a hyper memory: A single case TMS study on an individual with Highly Superior Autobiographical Memory

Highly Superior Autobiographical Memory (HSAM) is a rare ability to recall a profound number of personal events across one’s lifespan. HSAM recall is extremely quick, detailed and highly accurate, yet how autobiographical content is retrieved remains misunderstood. Here, we used transcranial magnetic stimulation (TMS) on a single HSAM case to identify specific brain areas causally involved in exceptional retrieval. Participant was shown several dates previously verified they had a memory for (i.e., verifiable event recall) while TMS was administered over visual areas (V1), left dorsolateral prefrontal cortex (DLPFC) or vertex (control) 500 ms after each date onset. Time to access memories in response to a date, nature of the memory (i.e., personal or factual), and ratings of whether access was direct or generative were recorded. Results found left DLPFC TMS significantly slowed down participant reaction time, while V1 stimulation caused a speeding up, with both effects specific to generative memory retrieval. This is the first neuromodulation study on an HSAM subject and provides evidence the left DLPFC is causally involved in HSAM elaboration. V1 effect is discussed in terms of addition-by-subtraction, hypothesising that V1 modulation allows other areas to increase efficiency.