Accessing Real-Life Episodic Information From Minutes Versus Hours Earlier Modulates Hippocampal and High-Order Cortical Dynamics

Cereb Cortex. 2016 Aug;26(8):3428-3441. doi: 10.1093/cercor/bhv155. Epub 2015 Aug 3.

Abstract

It is well known that formation of new episodic memories depends on hippocampus, but in real-life settings (e.g., conversation), hippocampal amnesics can utilize information from several minutes earlier. What neural systems outside hippocampus might support this minutes-long retention? In this study, subjects viewed an audiovisual movie continuously for 25 min; another group viewed the movie in 2 parts separated by a 1-day delay. Understanding Part 2 depended on retrieving information from Part 1, and thus hippocampus was required in the day-delay condition. But is hippocampus equally recruited to access the same information from minutes earlier? We show that accessing memories from a few minutes prior elicited less interaction between hippocampus and default mode network (DMN) cortical regions than accessing day-old memories of identical events, suggesting that recent information was available with less reliance on hippocampal retrieval. Moreover, the 2 groups evinced reliable but distinct DMN activity timecourses, reflecting differences in information carried in these regions when Part 1 was recent versus distant. The timecourses converged after 4 min, suggesting a time frame over which the continuous-viewing group may have relied less on hippocampal retrieval. We propose that cortical default mode regions can intrinsically retain real-life episodic information for several minutes.

Keywords: declarative memory; functional connectivity; intersubject correlation; naturalistic; timescales.

MeSH terms

  • Adolescent
  • Adult
  • Auditory Perception / physiology
  • Brain Mapping
  • Cerebral Cortex / diagnostic imaging
  • Cerebral Cortex / physiology*
  • Female
  • Hippocampus / diagnostic imaging
  • Hippocampus / physiology*
  • Humans
  • Magnetic Resonance Imaging
  • Male
  • Memory, Episodic*
  • Memory, Long-Term / physiology*
  • Memory, Short-Term / physiology*
  • Neural Pathways / physiology
  • Neuropsychological Tests
  • Time Factors
  • Video Recording
  • Visual Perception / physiology
  • Young Adult