Memory integration in humans with hippocampal lesions

Pajkert, Anna; Finke, Carsten; Shing, Yee Lee; Hoffmann, Martina; Sommer, Werner; Heekeren, Hauke R.; Ploner, Christoph J.

doi:10.1002/hipo.22766

Cited by 28 publications

(39 citation statements)

References 37 publications

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“…Our findings provide evidence that MTL structures, including the hippocampus, are essential to enabling the rapid integration of new information within stored knowledge in a schematic structure. These results align well with previous studies that revealed the critical role of the hippocampus in enabling inferential learning between different episodic events that overlap in the perceptual content in healthy individuals (Schlichting and Preston 2015;; and in patients with lesions in the MTL (Pajkert et al 2017).…”

Section: Discussionsupporting

confidence: 92%

Theta rhythm supports hippocampus-dependent integrative encoding in schematic memory networks

Nicolás

Sala-Padró

Cucurell

et al. 2019

Preprint

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Integrating new information into existing schematic structures of knowledge is the basis of learning in our everyday life activity as it enables structured representation of information and goal-directed behaviour in an ever-changing environment. However, how schematic mnemonic structures aid the integration of novel elements remains poorly understood. Here, we showed that the ability to integrate novel picture information into learn structures of picture associations that overlap by the same picture scene (associative network) or by the conceptually related scene information (schematic network) is hippocampus-dependent, as patients with lesions at the medial temporal lobe (including the hippocampus) were impaired in inferring novel relations between elements within these mnemonic networks but not in retrieving individual pictures in a subsequent memory test. In addition, we observed more persistent and widespread scalp electroencephalographic (EEG) theta oscillatory pattern (3-6Hz) while healthy participants encoded novel pictures related to schematic memory networks, suggesting that theta may reflect distances between elements within a representational network space. Finally, we found high similarity values for neural activity patterns elicited by novel and related events only within associative networks, thereby suggesting that neural reactivation may promote the integration of new information into existing memory networks only when direct associations within the network link their elements. These findings have important implications for our understanding of the neural mechanisms that support the development and organization of structures of knowledge.

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Section: Discussionsupporting

confidence: 92%

Theta rhythm supports hippocampus-dependent integrative encoding in schematic memory networks

Nicolás

Sala-Padró

Cucurell

et al. 2019

Preprint

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“…The formation of the integrative representation can be achieved either at encoding of BC (termed integrative encoding), or at retrieval (termed retrieval inference; [2]). As shown in Pajkert et al [14], across cycle, healthy middle-age participants showed an increasing reliance on integratively encoded representations for AC-decisions. That is, with repeated necessity of AC-decisions, participants might have increasingly tended to form integrated ABC-representations when encoding the BC-pairs (by reactivating the corresponding AB-pair).…”

Section: Introductionmentioning

confidence: 77%

“…In the current study, we compared children, adolescents, and young adults on their ability to form memory integration across overlapping associations. We examined memory inference using a modified version of the associative inference task [14]. Here, participants also learned a set of overlapping AB- (object-face) and BC- (face-object) associations and were then directly tested on memory of these associations (“direct” trials) and on inferential AC-associations (“inference” trials).…”

Section: Introductionmentioning

confidence: 99%

Integrating across memory episodes: Developmental trends

et al. 2019

Self Cite

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Memory enables us to use information from our past experiences to guide new behaviours, calling for the need to integrate or form inference across multiple distinct episodic experiences. Here, we compared children (aged 9–10 years), adolescents (aged 12–13 years), and young adults (aged 19–25 years) on their ability to form integration across overlapping associations in memory. Participants first encoded a set of overlapping, direct AB- and BC-associations (object-face and face-object pairs) as well as non-overlapping, unique DE-associations. They were then tested on these associations and inferential AC-associations. The experiment consisted of four such encoding/retrieval cycles, each consisting of different stimuli set. For accuracy on both unique and inferential associations, young adults were found to outperform teenagers, who in turn outperformed children. However, children were particularly slower than teenagers and young adults in making judgements during inferential than during unique associations. This suggests that children may rely more on making inferences during retrieval, by first retrieving the direct associations, followed by making the inferential judgement. Furthermore, young adults showed a higher correlation between accuracy in direct (AB, BC) and inferential AC-associations than children. This suggests that, young adults relied closely on AB- and BC-associations for making AC decisions, potentially by forming integrated ABC-triplets during encoding or retrieval. Taken together, our findings suggest that there may be an age-related shift in how information is integrated across experienced episodes, namely from relying on making inferences at retrieval during middle childhood to forming integrated representations at different memory processing stages in adulthood.

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“…In this division of labor, the hippocampus is thought to encode details of unfolding events and reactivate details of past events, while the mPFC is thought to find commonalities across episodes and bias hippocampal reactivation towards relevant past events (Preston & Eichenbaum, 2013). In line with these predictions, patients with lesions to either the mPFC (Spalding et al, 2018) or the hippocampus (Pajkert et al, 2017) suffer deficits in the memory integration that cannot be explained by deficits in associative memory alone. As the nature of these lesions did not change between encoding and inference, however, these studies do not clarify whether these regions specifically impair integrative encoding.…”

Section: Episodic Memories Are Integrated Across Event Boundariesmentioning

confidence: 91%

Event conjunction: How the hippocampus integrates episodic memories across event boundaries

Griffiths

Fuentemilla

2019

Hippocampus

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Our lives are a continuous stream of experience. Our episodic memories on the other hand have a definitive beginning, middle, and end. Theories of event segmentation suggest that salient changes in our environment produce event boundaries which partition the past from the present and, as a result, produce discretized memories. However, event boundaries cannot completely discretize two memories; any shared conceptual link will lead to the rapid integration of these memories. Here, we present a new framework inspired by electrophysiological research that resolves this apparent contradiction. At its heart, the framework proposes that hippocampal theta‐gamma coupling maintains a highly abstract model of an ongoing event and serves to encode this model as an episodic memory. When a second but related event begins, this theta‐gamma model is rapidly reconstructed within the hippocampus where new details of the second event can be appended to the existing event model. The event conjunction framework is the first electrophysiological explanation of how event memories can be formed at, and integrated across, event boundaries.

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Memory integration in humans with hippocampal lesions

Cited by 28 publications

References 37 publications

Theta rhythm supports hippocampus-dependent integrative encoding in schematic memory networks

Theta rhythm supports hippocampus-dependent integrative encoding in schematic memory networks

Integrating across memory episodes: Developmental trends

Event conjunction: How the hippocampus integrates episodic memories across event boundaries

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