Aging alters neural activity at event boundaries in the hippocampus and Posterior Medial network

Abstract

Recent research has highlighted a role for the hippocampus and a Posterior Medial cortical network in signaling event boundaries. However, little is known about whether or how these neural processes change over the course of healthy aging. Here, 546 cognitively normal participants 18–88 years old viewed a short movie while brain activity was measured using fMRI. The hippocampus and regions of the Posterior Medial network show increased activity at event boundaries, but these boundary-evoked responses decrease with age. Boundary-evoked activity in the posterior hippocampus predicts performance on a separate test of memory for stories, suggesting that hippocampal activity during event segmentation may be a broad indicator of individual differences in episodic memory ability. In contrast, boundary-evoked responses in the medial prefrontal cortex and middle temporal gyrus increase across the age range. These findings suggest that aging may alter neural processes for segmenting and remembering continuous real-world experiences.

Building bridges: the hippocampus constructs narrative memories across distant events

“…As shown in Figure 2B, these results reflect the fact that, as in previous studies (Baldassano et al, 2017;Ben-Yakov and Henson, 2018;Reagh et al, 2020), event boundaries evoked increases in hippocampal activation.…”

“…Research on event boundaries and memory has typically focused on how event segmentation breaks up continuous experiences. It follows that hippocampal activity increases at event boundaries (Baldassano et al, 2017;Ben-Yakov and Henson, 2018;Reagh et al, 2020) might reflect the process of segmenting experiences into distinct event representations. Although the present results do not rule out that possibility, our results suggest that boundary-evoked activity in the hippocampus may not only reflect a "wall" between events, but also a "bridge.…”

“…There is widespread agreement that the hippocampus plays a unique and necessary role in episodic memory (Addis et al, 2007;Eichenbaum et al, 2007;Scoville and Milner, 1957;Yonelinas et al, 2002). Furthermore, recent studies have demonstrated that during continuous viewing of naturalistic films, event boundaries evoke transient increases in activity in the hippocampus (Baldassano et al, 2017;Ben-Yakov and Henson, 2018;Reagh et al, 2020). Although these findings suggest that the hippocampus is recruited during event boundaries, the functional significance of boundary-evoked activity in the hippocampus remains unclear.…”

Mapping the organization and dynamics of the posterior medial network during movie watching

“…-Yakov & Henson as well asReagh et al (2020) in showing robust increases in activity at event boundaries across the PMN (Figure S2).Fig.S2. The change in activity between within-event time points and event transitions.…”

“…Regions of the PMN tend to function in a cohesive manner, exhibiting strong task-independent correlations in BOLD activity within the default network as well as task-related coactivation. Prior research has shown increased activity across the PMN during the recollection and construction of specific events (Benoit & Schacter, 2015;Rugg & Vilberg, 2013;Schacter et al, 2007;Spreng et al, 2009), network-wide multivariate representation of event-specific information (Chen et al, 2017;Robin et al, 2018), as well as reliable PMN responses to transitions between event contexts (Baldassano et al, 2017;Ben-Yakov & Henson, 2018;Reagh et al, 2020). Research that has directly modulated the PMN also supports its cohesive structure: non-invasive brain stimulation of left angular gyrus (AG) -a cortical gateway to the default network -increases both BOLD activity (Kim et al, 2018), and functional connectivity throughout the PMN during episodic tasks (Warren et al, 2019), confirming the strong functional dependence between these regions.…”