The perceptual richness of complex memory episodes is compromised by medial temporal lobe damage

Abstract

Perceptual richness, a defining feature of episodic memory, emerges from the reliving of multimodal sensory experiences. Although the importance of the medial temporal lobe (MTL) to episodic memory retrieval is well documented, the features that determine its engagement are not well characterized. The current study assessed the relationship between MTL function and episodic memory's perceptual richness. We designed a laboratory memory task meant to capture the complexity of memory for life episodes, while manipulating memory's perceptual content. Participants encoded laboratory episodes with rich (film clips) and impoverished (written narratives) perceptual content that were matched for other characteristics such as personal significance, emotionality and story content. At retrieval, participants were probed to describe the stories' perceptual features and storyline. Participants also recalled autobiographical memories (AMs) in a comparison condition. We compared the performance of patients with unilateral medial temporal lobe epilepsy (mTLE) and healthy controls to assess how damage to the MTL affects retrieval in these conditions. We observed an overall decrease in detail count in the mTLE group, along with a disproportionate deficit in perceptual details that was most acute in the AM and the perceptually enriched film clip conditions. Our results suggest that the impaired sense of reliving the past that accompanies MTL insult is mediated by a paucity of perceptual episodic memory details. We also introduce a new protocol that successfully mimics naturalistic memories while benefiting from the experimental control provided by using laboratory stimuli.

The influence of the hippocampus and declarative memory on word use: Patients with amnesia use less imageable words

“…The hippocampus, and its hallmark processing features of relational binding and representational flexibility, have long been linked to the formation and subsequent retrieval of highly detailed declarative (episodic) memory (Eichenbaum and Cohen, 2001). Hippocampal activation has been linked to the retrieval of highly detailed and vivid episodic (past and future) memories, and hippocampal damage has been shown to significantly reduce the number of perceptual details in narratives of episodic events (e.g., Addis et al, 2004; Hassabis et al, 2007; Kurczek et al, 2015; Race et al, 2011; Schacter and Addis, 2009; St-Laurent et al, 2014). We, and others, have also pointed to a multitude of ways that these same processing features of the hippocampus make direct contributions to language use and processing.…”

“…The relational binding of the perceptual, sensory, temporal, and spatial components of events reflects the flexible (re)construction and (re)instantiation of declarative (episodic) memories; this phenomenon has been linked to the hippocampus and other medial temporal lobe structures (MTL) (e.g., Eichenbaum and Cohen, 2001). The hippocampus and MTL have also been implicated in integration and retrieval of the perceptual details that constitute rich, vivid episodic memories across (e.g., Schacter and Addis, 2009; St-Laurent et al, 2014). Patients with hippocampal amnesia produce autobiographical narratives of past and future events that contain significantly fewer episodic details and that are described and rated as less vivid than those of healthy comparison participants (e.g., Hassabis et al, 2007; Kurczek et al, 2015; Race et al, 2011).…”

Neural changes associated with the generation of specific past and future events in depression

“…For instance, the vividness of AMs has been associated with the degree of hippocampal activity in healthy young (Addis et al, 2004;Addis and Schacter, 2008) (e.g., St Jacques et al, 2012). Moreover, the episodic richness of AMs is typically reduced in populations with hippocampal damage, including temporal lobe epilepsy (St-Laurent et al, 2014) and hippocampal amnesia . With respect to depression, reduced hippocampal volume in depressed individuals is well established (Campbell and MacQueen, 2004) and emerging evidence suggests that memory-related hippocampal activity may also be compromised (Fairhall et al, 2010).…”

Memory Assessment in the Clinical Context Using Functional Magnetic Resonance Imaging

“…2) 25,27,58 and patients with TLE demonstrate marked deficits in recalling details of autobiographical experiences. 29,31,59 Furthermore, mesial temporal damage in these patients results in a markedly reduced activation in the affected region and in the whole network of regions typically engaged during autobiographical recall. 9,60 Nonetheless, the author's group has found relatively poor correspondence between the magnitude or extent of hippocampal activation and performance on clinical memory tests, and even some negative correlations in certain tasks (McAndrews, unpublished data).…”