scholarly journals Human hippocampal neurons track moments in a sequence of events

2020 ◽  
Author(s):  
Leila Reddy ◽  
Benedikt Zoefel ◽  
Jessy K. Possel ◽  
Judith C. Peters ◽  
Doris Dijksterhuis ◽  
...  
Keyword(s):  
Episodic Memory ◽  
Hippocampal Neurons ◽  
Critical Role ◽  
Memory Task ◽  
Temporal Information ◽  
Firing Activity ◽  
Population Activity ◽  
Sequence Of Events ◽  
Human Hippocampus ◽  
Representation Of Time

AbstractAn indispensable feature of episodic memory is our ability to temporally piece together different elements of an experience into a coherent memory. Hippocampal “time cells” – neurons that represent temporal information – may play a critical role in this process. While these cells have been repeatedly found in rodents, it is still unclear to what extent similar temporal selectivity exists in the human hippocampus. Here we show that temporal context modulates the firing activity of human hippocampal neurons during structured temporal experiences. We recorded neuronal activity in the human brain while patients learned predictable sequences of pictures. We report that human time cells fire at successive moments in this task. Furthermore, time cells also signaled inherently changing temporal contexts during empty 10-second gap periods between trials, while participants waited for the task to resume. Finally, population activity allowed for decoding temporal epoch identity, both during sequence learning and during the gap periods. These findings suggest that human hippocampal neurons could play an essential role in temporally organizing distinct moments of an experience in episodic memory.Significance StatementEpisodic memory refers to our ability to remember the “what, where, and when” of a past experience. Representing time is an important component of this form of memory. Here, we show that neurons in the human hippocampus represent temporal information. This temporal signature was observed both when participants were actively engaged in a memory task, as well as during 10s-long gaps when they were asked to wait before performing the task. Furthermore, the activity of the population of hippocampal cells allowed for decoding one temporal epoch from another. These results suggest a robust representation of time in the human hippocampus.

scholarly journals Time cells in the human hippocampus and entorhinal cortex support episodic memory

2020 ◽  
Author(s):  
Gray Umbach ◽  
Pranish Kantak ◽  
Joshua Jacobs ◽  
Michael Kahana ◽  
Brad E. Pfeiffer ◽  
...  
Keyword(s):  
Episodic Memory ◽  
Entorhinal Cortex ◽  
Cell Activity ◽  
Memory Task ◽  
Temporal Information ◽  
Temporal Organization ◽  
Human Epilepsy ◽  
Human Hippocampus ◽  
Phase Precession ◽  
Episodic Memories

AbstractThe organization of temporal information is critical for the encoding and retrieval of episodic memories. In the rodent hippocampus and entorhinal cortex, recent evidence suggests that temporal information is encoded by a population of “time cells.” We identify time cells in humans using intracranial microelectrode recordings obtained from 27 human epilepsy patients who performed an episodic memory task. We show that time cell activity predicts the temporal organization of episodic memories. A significant portion of these cells exhibits phase precession, a key phenomenon not previously seen in human recordings. These findings establish a cellular mechanism for the representation of temporal information in the human brain needed to form episodic memories.

scholarly journals Time cells in the human hippocampus and entorhinal cortex support episodic memory

2020 ◽  
Vol 117 (45) ◽  
pp. 28463-28474 ◽  
Author(s):  
Gray Umbach ◽  
Pranish Kantak ◽  
Joshua Jacobs ◽  
Michael Kahana ◽  
Brad E. Pfeiffer ◽  
...  
Keyword(s):  
Episodic Memory ◽  
Entorhinal Cortex ◽  
Cell Activity ◽  
Memory Task ◽  
Cellular Mechanism ◽  
Temporal Information ◽  
Temporal Organization ◽  
Human Epilepsy ◽  
Human Hippocampus ◽  
Episodic Memories

The organization of temporal information is critical for the encoding and retrieval of episodic memories. In the rodent hippocampus and entorhinal cortex, evidence accumulated over the last decade suggests that populations of “time cells” in the hippocampus encode temporal information. We identify time cells in humans using intracranial microelectrode recordings obtained from 27 human epilepsy patients who performed an episodic memory task. We show that time cell activity predicts the temporal organization of retrieved memory items. We also uncover evidence of ramping cell activity in humans, which represents a complementary type of temporal information. These findings establish a cellular mechanism for the representation of temporal information in the human brain needed to form episodic memories.

scholarly journals Coding of episodic memory in the human hippocampus

2018 ◽  
Vol 115 (5) ◽  
pp. 1093-1098 ◽  
Author(s):  
John T. Wixted ◽  
Stephen D. Goldinger ◽  
Larry R. Squire ◽  
Joel R. Kuhn ◽  
Megan H. Papesh ◽  
...  
Keyword(s):  
Episodic Memory ◽  
Single Neuron ◽  
Large Fraction ◽  
Memory Task ◽  
Neuron Activity ◽  
Distributed Coding ◽  
Repeated Word ◽  
Human Hippocampus ◽  
Left Hippocampus ◽  
Episodic Memories

Neurocomputational models have long posited that episodic memories in the human hippocampus are represented by sparse, stimulus-specific neural codes. A concomitant proposal is that when sparse-distributed neural assemblies become active, they suppress the activity of competing neurons (neural sharpening). We investigated episodic memory coding in the hippocampus and amygdala by measuring single-neuron responses from 20 epilepsy patients (12 female) undergoing intracranial monitoring while they completed a continuous recognition memory task. In the left hippocampus, the distribution of single-neuron activity indicated that only a small fraction of neurons exhibited strong responding to a given repeated word and that each repeated word elicited strong responding in a different small fraction of neurons. This finding reflects sparse distributed coding. The remaining large fraction of neurons exhibited a concurrent reduction in firing rates relative to novel words. The observed pattern accords with longstanding predictions that have previously received scant support from single-cell recordings from human hippocampus.

Object, Space, and Object-Space Representations in the Primate Hippocampus

2005 ◽  
Vol 94 (1) ◽  
pp. 833-844 ◽  
Author(s):  
Edmund T. Rolls ◽  
Jianzhong Xiang ◽  
Leonardo Franco
Keyword(s):  
Episodic Memory ◽  
Spatial Information ◽  
Hippocampal Formation ◽  
Memory Task ◽  
Memory System ◽  
Important Advance ◽  
Object Space ◽  
Place Memory ◽  
Human Hippocampus ◽  
Spatial View

A fundamental question about the function of the primate including human hippocampus is whether object as well as allocentric spatial information is represented. Recordings were made from single hippocampal formation neurons while macaques performed an object-place memory task that required the monkeys to learn associations between objects and where they were shown in a room. Some neurons (10%) responded differently to different objects independently of location; other neurons (13%) responded to the spatial view independently of which object was present at the location; and some neurons (12%) responded to a combination of a particular object and the place where it was shown in the room. These results show that there are separate as well as combined representations of objects and their locations in space in the primate hippocampus. This is a property required in an episodic memory system, for which associations between objects and the places where they are seen are prototypical. The results thus provide an important advance by showing that a requirement for a human episodic memory system, separate and combined neuronal representations of objects and where they are seen “out there” in the environment, is present in the primate hippocampus.

scholarly journals Crucial role for CA2 inputs in the sequential organization of CA1 time cells supporting memory

2021 ◽  
Vol 118 (3) ◽  
pp. e2020698118
Author(s):  
Christopher J. MacDonald ◽  
Susumu Tonegawa
Keyword(s):  
Spatial Working Memory ◽  
Temporal Structure ◽  
Critical Role ◽  
Cell Activity ◽  
Memory Task ◽  
Choice Point ◽  
Temporal Coding ◽  
Temporal Information ◽  
Spatial Coding ◽  
Dorsal Hippocampal

There is considerable evidence for hippocampal time cells that briefly activate in succession to represent the temporal structure of memories. Previous studies have shown that time cells can be disrupted while leaving place cells intact, indicating that spatial and temporal information can be coded in parallel. However, the circuits in which spatial and temporal information are coded have not been clearly identified. Here we investigated temporal and spatial coding by dorsal hippocampal CA1 (dCA1) neurons in mice trained on a classic spatial working-memory task. On each trial, the mice approached the same choice point on a maze but were trained to alternate between traversing one of two distinct spatial routes (spatial coding phase). In between trials, there was a 10-s mnemonic delay during which the mouse continuously ran in a fixed location (temporal coding phase). Using cell-type–specific optogenetic methods, we found that inhibiting dorsal CA2 (dCA2) inputs into dCA1 degraded time cell coding during the mnemonic delay and impaired the mouse’s subsequent memory-guided choice. Conversely, inhibiting dCA2 inputs during the spatial coding phase had a negligible effect on place cell activity in dCA1 and no effect on behavior. Collectively, our work demonstrates that spatial and temporal coding in dCA1 is largely segregated with respect to the dCA2–dCA1 circuit and suggests that CA2 plays a critical role in representing the flow of time in memory within the hippocampal network.

scholarly journals Memory for Dynamic Events When Event Boundaries Are Accentuated With Emotional Stimuli

2021 ◽  
Vol 7 (1) ◽  
Author(s):  
Jared J. Peterson ◽  
Jennica S. Rogers ◽  
Heather R. Bailey
Keyword(s):  
Episodic Memory ◽  
Mental Model ◽  
Temporal Order ◽  
Temporal Information ◽  
Emotional Stimuli ◽  
Ongoing Activity ◽  
Dynamic Events ◽  
Sequence Of Events ◽  
Event Information ◽  
Continuous Activities

Event boundaries are important moments throughout an ongoing activity that influence perception and memory. They allow people to parse continuous activities into meaningful events, encode the temporal sequence of events and bind event information together in episodic memory (DuBrow & Davachi, 2013). Thus, drawing attention to event boundaries may facilitate these important perceptual and encoding processes. In the current study, we used emotionally arousing stimuli to guide attention to event boundaries because this type of stimulus has been shown to influence perception and attention. We evaluated whether accentuating event boundaries with commercials improves memory and whether emotional stimuli further enhance this effect. A total of 97 participants watched a television episode in which we manipulated commercial break locations (boundary, non-boundary, no commercial) and the type of commercial (emotional, neutral) and then completed memory tasks. Overall, placing emotionally arousing commercials at event boundaries increased memory for the temporal order of events, but no other effects of accentuating event boundaries were observed. Thus, drawing attention to event boundaries—via emotionally charged commercials—increases the likelihood that people will perceive the change in events, update their mental model accordingly and better integrate temporal information from the just-encoded event.

scholarly journals Multilab Direct Replication of Flavell, Beach, and Chinsky (1966): Spontaneous Verbal Rehearsal in a Memory Task as a Function of Age

2021 ◽  
Vol 4 (2) ◽  
pp. 251524592110181
Author(s):  
Emily M. Elliott ◽  
Candice C. Morey ◽  
Angela M. AuBuchon ◽  
Nelson Cowan ◽  
Chris Jarrold ◽  
...  
Keyword(s):  
Cognitive Development ◽  
Young Children ◽  
Memory Performance ◽  
Critical Role ◽  
Memory Task ◽  
Older Children ◽  
Continuous Increase ◽  
Verbal Rehearsal ◽  
Picture Memory ◽  
Spontaneous Production

Work by Flavell, Beach, and Chinsky indicated a change in the spontaneous production of overt verbalization behaviors when comparing young children (age 5) with older children (age 10). Despite the critical role that this evidence of a change in verbalization behaviors plays in modern theories of cognitive development and working memory, there has been only one other published near replication of this work. In this Registered Replication Report, we relied on researchers from 17 labs who contributed their results to a larger and more comprehensive sample of children. We assessed memory performance and the presence or absence of verbalization behaviors of young children at different ages and determined that the original pattern of findings was largely upheld: Older children were more likely to verbalize, and their memory spans improved. We confirmed that 5- and 6-year-old children who verbalized recalled more than children who did not verbalize. However, unlike Flavell et al., substantial proportions of our 5- and 6-year-old samples overtly verbalized at least sometimes during the picture memory task. In addition, continuous increase in overt verbalization from 7 to 10 years old was not consistently evident in our samples. These robust findings should be weighed when considering theories of cognitive development, particularly theories concerning when verbal rehearsal emerges and relations between speech and memory.

scholarly journals Are visual working memory and episodic memory distinct processes? Insight from stroke patients by lesion-symptom mapping

2021 ◽  
Author(s):  
Selma Lugtmeijer ◽  
◽  
Linda Geerligs ◽  
Frank Erik de Leeuw ◽  
Edward H. F. de Haan ◽  
...  
Keyword(s):  
Working Memory ◽  
Episodic Memory ◽  
Visual Working Memory ◽  
Visual Memory ◽  
Right Hemisphere ◽  
Memory Task ◽  
Stroke Patients ◽  
Lesion Symptom Mapping ◽  
Criterion Setting ◽  
The Right

AbstractWorking memory and episodic memory are two different processes, although the nature of their interrelationship is debated. As these processes are predominantly studied in isolation, it is unclear whether they crucially rely on different neural substrates. To obtain more insight in this, 81 adults with sub-acute ischemic stroke and 29 elderly controls were assessed on a visual working memory task, followed by a surprise subsequent memory test for the same stimuli. Multivariate, atlas- and track-based lesion-symptom mapping (LSM) analyses were performed to identify anatomical correlates of visual memory. Behavioral results gave moderate evidence for independence between discriminability in working memory and subsequent memory, and strong evidence for a correlation in response bias on the two tasks in stroke patients. LSM analyses suggested there might be independent regions associated with working memory and episodic memory. Lesions in the right arcuate fasciculus were more strongly associated with discriminability in working memory than in subsequent memory, while lesions in the frontal operculum in the right hemisphere were more strongly associated with criterion setting in subsequent memory. These findings support the view that some processes involved in working memory and episodic memory rely on separate mechanisms, while acknowledging that there might also be shared processes.

scholarly journals Effects of ketamine on brain function during metacognition of episodic memory

2021 ◽  
Vol 2021 (1) ◽  
Author(s):  
Mirko Lehmann ◽  
Claudia Neumann ◽  
Sven Wasserthal ◽  
Johannes Schultz ◽  
Achilles Delis ◽  
...  
Keyword(s):  
Episodic Memory ◽  
Parietal Lobe ◽  
Memory Task ◽  
Reaction Times ◽  
Neural Correlates ◽  
Double Blind ◽  
Lingual Gyrus ◽  
States Of Consciousness ◽  
Fmri Study ◽  
Confidence Ratings

Abstract Only little research has been conducted on the pharmacological underpinnings of metacognition. Here, we tested the modulatory effects of a single intravenous dose (100 ng/ml) of the N-methyl-D-aspartate-glutamate-receptor antagonist ketamine, a compound known to induce altered states of consciousness, on metacognition and its neural correlates. Fifty-three young, healthy adults completed two study phases of an episodic memory task involving both encoding and retrieval in a double-blind, placebo-controlled fMRI study. Trial-by-trial confidence ratings were collected during retrieval. Effects on the subjective state of consciousness were assessed using the 5D-ASC questionnaire. Confirming that the drug elicited a psychedelic state, there were effects of ketamine on all 5D-ASC scales. Acute ketamine administration during retrieval had deleterious effects on metacognitive sensitivity (meta-d′) and led to larger metacognitive bias, with retrieval performance (d′) and reaction times remaining unaffected. However, there was no ketamine effect on metacognitive efficiency (meta-d′/d′). Measures of the BOLD signal revealed that ketamine compared to placebo elicited higher activation of posterior cortical brain areas, including superior and inferior parietal lobe, calcarine gyrus, and lingual gyrus, albeit not specific to metacognitive confidence ratings. Ketamine administered during encoding did not significantly affect performance or brain activation. Overall, our findings suggest that ketamine impacts metacognition, leading to significantly larger metacognitive bias and deterioration of metacognitive sensitivity as well as unspecific activation increases in posterior hot zone areas of the neural correlates of consciousness.

The Effect of Divided Attention on Encoding and Retrieval in Episodic Memory Revealed by Positron Emission Tomography

2000 ◽  
Vol 12 (2) ◽  
pp. 267-280 ◽  
Author(s):  
Tetsuya Iidaka ◽  
Nicole D. Anderson ◽  
Shitij Kapur ◽  
Roberto Cabez ◽  
Fergus I. M. Craik
Keyword(s):  
Positron Emission Tomography ◽  
Prefrontal Cortex ◽  
Episodic Memory ◽  
Divided Attention ◽  
Memory Performance ◽  
Memory Task ◽  
Anterior Cingulate ◽  
Emission Tomography ◽  
Positron Emission ◽  
Encoding And Retrieval

The effects of divided attention (DA) on episodic memory encoding and retrieval were investigated in 12 normal young subjects by positron emission tomography (PET). Cerebral blood flow was measured while subjects were concurrently performing a memory task (encoding and retrieval of visually presented word pairs) and an auditory tone-discrimination task. The PET data were analyzed using multivariate Partial Least Squares (PLS), and the results revealed three sets of neural correlates related to specific task contrasts. Brain activity, relatively greater under conditions of full attention (FA) than DA, was identified in the occipital-temporal, medial, and ventral-frontal areas, whereas areas showing relatively more activity under DA than FA were found in the cerebellum, temporo-parietal, left anterior-cingulate gyrus, and bilateral dorsolateral-prefrontal areas. Regions more active during encoding than during retrieval were located in the hippocampus, temporal and the prefrontal cortex of the left hemisphere, and regions more active during retrieval than during encoding included areas in the medial and right-prefrontal cortex, basal ganglia, thalamus, and cuneus. DA at encoding was associated with specific decreases in rCBF in the left-prefrontal areas, whereas DA at retrieval was associated with decreased rCBF in a relatively small region in the right-prefrontal cortex. These different patterns of activity are related to the behavioral results, which showed a substantial decrease in memory performance when the DA task was performed at encoding, but no change in memory levels when the DA task was performed at retrieval.

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