scholarly journals Neural Population Evidence of Functional Heterogeneity along the CA3 Transverse Axis: Pattern Completion versus Pattern Separation

Neuron ◽  
2015 ◽  
Vol 87 (5) ◽  
pp. 1093-1105 ◽  
Author(s):  
Heekyung Lee ◽  
Cheng Wang ◽  
Sachin S. Deshmukh ◽  
James J. Knierim
Keyword(s):  
Pattern Separation ◽  
Neural Population ◽  
Functional Heterogeneity ◽  
Transverse Axis ◽  
Pattern Completion

scholarly journals Heterogeneity of age-related neural hyperactivity along the CA3 transverse axis

2020 ◽  
Author(s):  
Heekyung Lee ◽  
Zitong Wang ◽  
Scott Zeger ◽  
Michela Gallagher ◽  
James J. Knierim
Keyword(s):  
Memory Deficits ◽  
Normal Function ◽  
Pattern Separation ◽  
Aged Rats ◽  
Functional Heterogeneity ◽  
Transverse Axis ◽  
Pattern Completion ◽  
Opposite Trend ◽  
Age Related ◽  
Ca3 Neurons

AbstractAge-related memory deficits are correlated with neural hyperactivity in the CA1 and CA3 regions of the hippocampus. Abnormal CA3 hyperactivity in aged rats has been proposed to contribute to an imbalance between the normal tradeoff between pattern separation and pattern completion, resulting in overly rigid representations. Recent evidence of functional heterogeneity along the CA3 transverse axis suggests that proximal CA3 supports pattern separation while distal CA3 supports pattern completion. It is not known whether age-related CA3 hyperactivity is uniformly represented along the CA3 transverse axis. We examined the firing rates of CA3 neurons from male young and aged Long-Evans rats along the CA3 transverse axis. Consistent with prior studies, young CA3 cells showed an increasing gradient in mean firing rate from proximal to distal CA3. However, aged CA3 cells showed an opposite trend, with a decreasing gradient from proximal to distal CA3. Thus, CA3 cells in aged rats were hyperactive in proximal CA3, but possibly hypoactive in distal CA3, compared to young rats. We suggest that, in combination with altered inputs from the entorhinal cortex and dentate gyrus, the proximal CA3 region of aged rats may switch from its normal function that reflects the pattern separation output of the DG and instead performs a computation that reflects an abnormal bias toward pattern completion. In parallel, distal CA3 of aged rats may create weaker attractor basins that promote bistable representations under certain conditions.

scholarly journals Proximal CA3 is the primary locus of age-related pattern separation deficits in rats

2021 ◽  
Author(s):  
Heekyung Lee ◽  
Arjuna Tilekeratne ◽  
Nick Lukish ◽  
Zitong Wang ◽  
Scott Zeger ◽  
...  
Keyword(s):  
Neural Coding ◽  
Pattern Separation ◽  
Transverse Axis ◽  
Pattern Completion ◽  
Memory Processing ◽  
Functional Gradient ◽  
Environmental Similarity ◽  
Age Related ◽  
Normal Transition ◽  
Homogeneous Network

AbstractAge-related deficits in pattern separation have been postulated to bias the output of hippocampal memory processing toward pattern completion, which can cause deficits in accurate memory retrieval. While the CA3 region of the hippocampus is often conceptualized as a homogeneous network involved in pattern completion, growing evidence demonstrates a functional gradient in CA3 along the transverse axis, with proximal CA3 supporting pattern separation and distal CA3 supporting pattern completion. We examined the neural representations along the CA3 transverse axis in young (Y), aged memory-unimpaired (AU), and aged memory-impaired (AI) rats when different changes were made to the environment. When the environmental similarity was high (e.g., altered cues or altered environment shapes in the same room), Y and AU rats showed more orthogonalized representations in proximal CA3 than in distal CA3, consistent with prior studies showing a functional dissociation along the transverse axis of CA3. In contrast, AI rats showed less orthogonalization in proximal CA3 than Y and AU rats but showed more normal (i.e., generalized) representations in distal CA3, with little evidence of a functional gradient. When the environmental similarity was low (e.g., recordings were done in different rooms), representations in proximal and distal CA3 remapped in all rats, showing that AI rats are able to dissociate representations when inputs show greater dissimilarity. These results provide evidence that the aged-related bias towards pattern completion is due to the loss in AI rats of the normal transition from pattern separation to pattern completion along the CA3 transverse axis and, furthermore, that proximal CA3 is the primary locus of this age-related dysfunction in neural coding.

scholarly journals Pattern separation is the key driver of expectation-modulated memory

2019 ◽  
Author(s):  
Darya Frank ◽  
Daniela Montaldi
Keyword(s):  
Memory Performance ◽  
Recognition Task ◽  
Discrimination Performance ◽  
Pattern Separation ◽  
Cognitive Factors ◽  
Previous Trial ◽  
Pattern Completion ◽  
Logical Deduction ◽  
Key Driver

AbstractThe hippocampus uses pattern separation and pattern completion in a continuous manner to successfully encode and retrieve memories1,2. However, whether and how cognitive factors might modulate the dynamics between these types of computation is not well understood. Here we examine the role of expectation in shifting the hippocampus to perform pattern separation. Expectation can be built up through multiple contextual exposures leading to prediction (as in a learnt contingency) or through logical deduction based on a previous mnemonic response. Participants first learned a contingency between a cue and an object’s category (man-made or natural). Then, at encoding, one third of the cues that preceded the to-be-memorised objects violated the studied rule. At test, participants performed an old/new recognition task with old items (targets) and a set of parametrically manipulated (very similar to dissimilar) new foils for each object. We explored the effects of both contextual expectation, manipulated at initial encoding, and mnemonic-attribution expectation, driven by the mnemonic decisions taken on previous retrieval trials. For example, a target would be unexpected if in a previous trial a similar foil had been erroneously accepted as old. Memory was found to be better for foils of high and mid similarity to contextually unexpected targets at encoding, compared to expected ones. Additionally, violations of mnemonic-attribution expectation also yielded improved memory performance when the level of foil similarity was high. These results suggest that violations of both contextual expectation and mnemonic-attribution expectation engage pattern separation, resulting in better discrimination performance for these items. Importantly, this mechanism is engaged when input differentiation is required in order to make a correct recognition decision.

scholarly journals The Contributions of Eye Gaze Fixations and Target-Lure Similarity to Behavioral and fMRI Indices of Pattern Separation and Pattern Completion

2021 ◽  
Author(s):  
Daniel K Bjornn ◽  
Julie Van ◽  
Brock Kirwan
Keyword(s):  
Eye Movements ◽  
False Alarm ◽  
Eye Movement ◽  
Eye Gaze ◽  
Recognition Task ◽  
Discrimination Performance ◽  
Pattern Separation ◽  
Fmri Data ◽  
Pattern Completion ◽  
Gaze Fixations

Pattern separation and pattern completion are generally studied in humans using mnemonic discrimination tasks such as the Mnemonic Similarity Task (MST) where participants identify similar lures and repeated items from a series of images. Failures to correctly discriminate lures are thought to reflect a failure of pattern separation and a propensity toward pattern completion. Recent research has challenged this perspective, suggesting that poor encoding rather than pattern completion accounts for the occurrence of false alarm responses to similar lures. In two experiments, participants completed a continuous recognition task version of the MST while eye movement (Experiment 1 and 2) and fMRI data (Experiment 2) were collected. While we replicated the result that fixation counts at study predicted accuracy on lure trials, we found that target-lure similarity was a much stronger predictor of accuracy on lure trials across both experiments. Lastly, we found that fMRI activation changes in the hippocampus were significantly correlated with the number of fixations at study for correct but not incorrect mnemonic discrimination judgments when controlling for target-lure similarity. Our findings indicate that while eye movements during encoding predict subsequent hippocampal activation changes, mnemonic discrimination performance is better described by pattern separation and pattern completion processes that are influenced by target-lure similarity than simply poor encoding.

scholarly journals Pattern separation and pattern completion: Behaviorally separable processes?

2020 ◽  
Author(s):  
Chi T. Ngo ◽  
Sebastian Michelmann ◽  
Ingrid R. Olson ◽  
Nora S. Newcombe
Keyword(s):  
Pattern Separation ◽  
Pattern Completion

scholarly journals Amplified Mnemonic Discrimination and Attenuated Generalization Are Associated with Positive Schizotypy

2020 ◽  
Author(s):  
Ágota Vass ◽  
becske melinda ◽  
Agnes Szollosi ◽  
Mihály Racsmány ◽  
Bertalan Polner
Keyword(s):  
False Recognition ◽  
Pattern Separation ◽  
Small Samples ◽  
Future Research ◽  
Healthy Population ◽  
Pattern Completion ◽  
Memory Impairments ◽  
Hippocampal Dysfunction ◽  
Neural Computations ◽  
Underlying Mechanisms

Memory dysfunction has been first recognized in patients with schizophrenia over 100 years ago and it is considered to be a particularly pronounced symptom of the illness. According to the hippocampal dysfunction theory, memory impairments and positive symptoms of schizophrenia such as hallucinations and delusions might be attributable to an unbalance in the interplay of pattern separation and pattern completion neural computations. While the theory addresses alterations specifically related to schizophrenia, schizotypy (a personality construct that encompasses schizophrenia symptom-like traits) is increasingly considered to be a useful construct for conceptualizing the development and expression of schizophrenia. Behavioural studies in patients with schizophrenia have come to disparate findings when testing the hippocampal dysfunction theory and are not devoid of some of the limitations and confounds that are commonly encountered in schizophrenia research, such as small samples, and a possible modulating effect of medications on cognitive performance. The present study aims to reconcile this debate by investigating the relationship between positive schizotypy and lure discrimination index and false recognition of lures (putative behavioural indicators of pattern separation and completion, respectively) in a sample of healthy individuals (N=71) varying in terms of self-reported unusual experiences. Contradicting our expectations (which were based on patient studies), positive schizotypy in the healthy population was associated with enhanced mnemonic discrimination and attenuated false recognition of lures. The current study is the first ever to investigate pattern separation and pattern completion in relation to different schizotypy dimensions. We address possible underlying mechanisms that might cause a lower false recognition of lures (e.g. impaired ability to generalise) in schizotypy. Resemblance between positive schizotypy and schizophrenia could not be detected at the level of behavioural performance which can be interpreted in a theoretical framework of hippocampal neural computations . Uncovering the underlying mechanisms of this discrepancy awaits future research.

scholarly journals Pattern separation and pattern completion for human face identity recognition in prodromal Alzheimer’s disease

2021 ◽  
Vol 17 (S6) ◽  
Author(s):  
Lisa Quenon ◽  
Bruno Rossion ◽  
John L. Woodard ◽  
Bernard J Hanseeuw ◽  
Laurence Dricot ◽  
...  
Keyword(s):  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Pattern Separation ◽  
Human Face ◽  
Pattern Completion ◽  
Identity Recognition ◽  
Face Identity ◽  
Prodromal Alzheimer’S Disease

scholarly journals Spatial pattern completion deficits in older adults

2021 ◽  
Author(s):  
Meera Paleja ◽  
Julia Spaniol
Keyword(s):  
Older Adults ◽  
Spatial Pattern ◽  
Age Differences ◽  
Computational Models ◽  
Pattern Separation ◽  
Pattern Completion ◽  
Completion Task ◽  
Age Related ◽  
Baseline Task ◽  
Cue Availability

Aging may have an impact on the CA3 autoassociative network of the hippocampus, posited by computational models as supporting pattern completion. Twenty-five young (YAs) and 25 older adults (OAs) performed a spatial pattern completion task using a computerized navigational paradigm analogous to a rodent pattern completion task reliant on the CA3. Participants identified a previously seen goal location, and the availability of distal cues in the environment was manipulated such that 0, 2, or 4 cues were missing. Performance in both groups declined as a function of decreased cue availability. However, controlling for age differences in task performance during a pre-experimental baseline task, OAs performed equivalently to YAs when all cues were available, but worse than YAs as the number of cues decreased. These findings suggest spatial pattern completion may be impaired in OAs. We discuss these findings in the context of a growing body of literature suggesting age-related imbalances in pattern separation vs. pattern completion.

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