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

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. Further information
available in dataset README file.

众所周知，新情景记忆的形成依赖于海马体，但在现实场景中（如对话），海马体失忆症患者能够利用几分钟前的信息。海马体之外的哪些神经系统可能支持这种长达数分钟的信息保留？本研究中，一组被试连续观看一段视听电影25分钟；另一组被试则分两部分观看该电影，两部分之间间隔1天。理解第二部分的内容依赖于检索第一部分的信息，因此在延迟一天的条件下需要海马体的参与。但获取几分钟前的相同信息是否也需要同等程度的海马体激活呢？我们发现，与获取相同事件的一天前记忆相比，获取几分钟前的记忆引发海马体与默认模式网络（DMN）皮层区域之间的互动更少，这表明近期信息的获取对海马体检索的依赖程度较低。此外，两组被试表现出可靠但独特的DMN活动时间进程，反映了当第一部分信息为近期与远期时，这些区域所承载的信息存在差异。4分钟后，两组的时间进程趋同，这表明连续观看组在该时间范围内可能较少依赖海马体检索。我们提出，皮层默认模式区域能够内在地保留现实情景信息达数分钟之久。更多信息可参见数据集的README文件。