Selective enhancement of memory access in individuals with superior autobiographical memory: An fMRI study

Introduction: Neurobiological mechanisms underlying human memory have been classically investigated through patients with selective memory disorders. The discovery of individuals spontaneously showing highly superior autobiographical memory (HSAM) provides instead an extraordinary chance to investigate which are the possible correlates of enhanced human memory. Specifically, here we asked whether HSAM rely on enhanced access or enhanced reliving of existing memories. Methods: During fMRI, HSAM and normotypical memory individuals were asked to access and relive autobiographical memories (AM) with specific spatiotemporal coordinates (e.g. “The first time you drove a car”). Participants had to confirm the appearance of the AM through a response button, thus defining the “memory access” phase, and then continue to relive the retrieved event in as much detail as possible, i.e., the “memory reliving” phase. Participants then had to rate both the emotional and reliving level of the retrieved AM. The specificity of AM activations was controlled by subtracting neural activity needed to participants for accessing and generating information from semantic memory, SM (e.g., “Examples of vegetables”). Post-scanning, participants were asked to provide details about memories retrieved during the experiment. Results: Behaviorally, HSAM individuals were faster in accessing AMs and reported more details than controls. The fMRI results revealed increased activation in HSAM vs. control individuals during access to AMs. This effect involved a left-lateralized network of regions including the ventro- and dorso-medial prefrontal cortex, and the temporo-parietal junction. The analysis of functional connectivity revealed that memory access in HSAM was further sustained by other core regions of memory processes, such as the hippocampus in the medial temporal lobe, the anterior cingulate cortex and the posterior parietal cortex. Conversely, we found no differences between the two groups during memory reliving. Conclusions: The enhanced recruitment of neural resources during access but not reliving of AM suggests a comparable “quality” of memory traces in the two groups, with HSAM individuals equipped with a more efficient mechanism devoted to AM search and access. Overall, the current findings highlight how the comparison between HSAM and normotypical memory individuals allows to unravel fundamental neurobiological mechanisms underlying human memory.