Medial Temporal Lobe Function and the Perceptual Richness of Memory for Complex Personal and Laboratory Events

Reliving the past requires the integration of multi-modal sensory details into a coherent mental impression of the initial event. In most people, memory for life episodes, or Autobiographical Memory (AM), is rich in sensory-perceptual elements that provide the vivid impression of travelling back in time. Abundant evidence indicates that the hippocampus plays a central role in AM recollection, but much research is still needed to determine which AM attributes engage the hippocampus at retrieval. My work assessed the relationship between hippocampal function and the perceptual richness of memory episodes. I designed a paradigm that captured the complexity of AM, and that manipulated perceptual richness while controlling for other AM confounds, such as recency, rehearsal, personal relevance, and “story” content. Participants studied and recalled perceptually enriched and impoverished laboratory events (film clips and written narratives, respectively) matched for the complexity of their storyline. An AM condition was also included for comparison. I tested healthy individuals and participants with unilateral medial temporal lobe epilepsy (mTLE), a clinical population with well documented hippocampal damage, on this paradigm. Perceptual richness was greatly reduced in people with mTLE, an effect that was most salient in the perceptually enriched conditions (AM and film clips). In a functional MRI version of this paradigm conducted on healthy individuals, I identified neural regions sensitive to the perceptual richness of AM and laboratory events, which included the anterior portion of the right hippocampus and other regions known to play a role in imagery and visual processing. In patients with right-lateralized mTLE, activation in these brain regions was markedly reduced in all memory conditions, which was consistent with the reduced perceptual richness I observed behaviourally. I reveal a clear relationship between hippocampal function and the perceptual richness of episodic memory, suggesting that the hippocampus plays a central role among brain regions that support the integration of multi-modal details into enriched memory experiences. My findings also advance our knowledge of how pathology and the nature of memory representation affect the neural correlates of episodic memory.Ph