Successful memory formation is driven by contextual encoding in the core memory network

Long, Nicole M.; Kahana, Michael J.

doi:10.1016/j.neuroimage.2015.06.073

Cited by 73 publications

(67 citation statements)

References 60 publications

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“…In a previous study (Long & Kahana, 2015) we found that high frequency activity (HFA, 44 – 100Hz) increases as a function of subsequent temporal clustering; however, as we did not control for semantic relatedness among study words, temporally clustered words could also have been clustered based on semantic associations. Therefore, we were unable to dissociate the contributions of episodic and semantic processing.…”

Section: Resultsmentioning

confidence: 75%

Modulation of task demands suggests that semantic processing interferes with the formation of episodic associations.

Long

Kahana

2017

Journal of Experimental Psychology: Learning, Memory, and Cogni

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Although episodic and semantic memory share overlapping neural mechanisms, it remains unclear how our pre-existing semantic associations modulate the formation of new, episodic associations. When freely recalling recently studied words, people rely on both episodic and semantic associations, shown through temporal and semantic clustering of responses. We asked whether orienting participants toward semantic associations interferes with or facilitates the formation of episodic associations. We compared electroencephalographic (EEG) activity recorded during the encoding of subsequently recalled words that were either temporally or semantically clustered. Participants studied words with or without a concurrent semantic orienting task. We identified a neural signature of successful episodic association formation whereby high frequency EEG activity (HFA, 44 – 100 Hz) overlying left prefrontal regions increased for subsequently temporally clustered words, but only for those words studied without a concurrent semantic orienting task. To confirm that this disruption in the formation of episodic associations was driven by increased semantic processing, we measured the neural correlates of subsequent semantic clustering. We found that HFA increased for subsequently semantically clustered words only for lists with a concurrent semantic orienting task. This dissociation suggests that increased semantic processing of studied items interferes with the neural processes that support the formation of novel episodic associations.

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Section: Resultsmentioning

confidence: 75%

Modulation of task demands suggests that semantic processing interferes with the formation of episodic associations.

Long

Kahana

2017

Journal of Experimental Psychology: Learning, Memory, and Cogni

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“…As an alternative to an attention-based account, common changes in spectral power may reflect cognitive operations supporting the maintenance and integration of episodic content (Polyn and Kahana, 2008). Recent work examining the electrophysiological correlates of episodic encoding (Long and Kahana, 2015) argues that increased neural activity within left prefrontal, lateral temporal, and MTL sites reflects processing that supports the formation of episodic memories (i.e., the association of information within a spatiotemporal context), as it predicts subsequent temporal organization of learned information. Our findings build upon this work, and suggest that the operations supported by this network are not specific to the encoding of memories, as they facilitate the retrieval of previously learned content.…”

Section: Discussionmentioning

confidence: 99%

Similar patterns of neural activity predict memory function during encoding and retrieval

et al. 2017

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Neural networks that span the medial temporal lobe (MTL), prefrontal cortex, and posterior cortical regions are essential to episodic memory function in humans. Encoding and retrieval are supported by the engagement of both distinct neural pathways across the cortex and common structures within the medial temporal lobes. However, the degree to which memory performance can be determined by neural processing that is common to encoding and retrieval remains to be determined. To identify neural signatures of successful memory function, we administered a delayed free-recall task to 187 neurosurgical patients implanted with subdural or intraparenchymal depth electrodes. We developed multivariate classifiers to identify patterns of spectral power across the brain that independently predicted successful episodic encoding and retrieval. During encoding and retrieval, patterns of increased high frequency activity in prefrontal, MTL, and inferior parietal cortices, accompanied by widespread decreases in low frequency power across the brain predicted successful memory function. Using a cross-decoding approach, we demonstrate the ability to predict memory function across distinct phases of the free-recall task. Furthermore, we demonstrate that classifiers that combine information from both encoding and retrieval states can outperform task-independent models. These findings suggest that the engagement of a core memory network during either encoding or retrieval shapes the ability to remember the past, despite distinct neural interactions that facilitate encoding and retrieval.

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“…Probing rat hippocampal neurons in vitro, Bi and Poo (1998) showed that the postsynaptic neuron must fire 20 ms (that is, 1 cycle of a gamma oscillation) after the presynaptic neuron to induce LTP. Given that these hippocampal neurons have been shown to lock gamma-band activity (Jutras, Fries, & Buffalo, 2009) and hippocampal gamma-band activity is predictive of memory formation (e.g., Griffiths et al, 2019;Long & Kahana, 2015), one could speculate that increases in the amplitude of hippocampal gamma oscillations reflect increases in STDP.…”

Section: A Role For Neural Oscillationsmentioning

confidence: 99%

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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Successful memory formation is driven by contextual encoding in the core memory network

Cited by 73 publications

References 60 publications

Modulation of task demands suggests that semantic processing interferes with the formation of episodic associations.

Modulation of task demands suggests that semantic processing interferes with the formation of episodic associations.

Similar patterns of neural activity predict memory function during encoding and retrieval

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

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