scholarly journals Investigating the role of dendrites in pattern separation: A computational approach

2015 ◽  
Author(s):  
Spyridon Chavlis ◽  
Panagiotis C. Petrantonakis ◽  
Panayiota Poirazi
Keyword(s):  
Granule Cells ◽  
Separation Efficiency ◽  
Hamming Distance ◽  
Morphological Characteristics ◽  
Pattern Separation ◽  
Biologically Relevant ◽  
Preliminary Results ◽  
Neuronal Types ◽  
The Brain

Objectives: In order to distinguish similar memories, it is experimentally confirmed that the hippocampus forms distinct representations of them. The ability of the brain to disambiguate memories is known as pattern separation. It has been proposed that dentate gyrus (DG) accomplishes this task, specifically through its principal cells, called granule cells (GCs). In this project we investigate the role of GC dendrites in pattern separation by modifying their biophysical and morphological characteristics. Methods & Results: We have implemented a morphologically simple, yet biologically relevant, computational model of the DG that implements pattern separation. The network consists of four well-studied neuronal types: granule, mossy, basket, and HIPP cells. The GC model consists of an integrate-and-fire somatic compartment connected to a variable numbers of active dendritic compartments. For simplicity reasons, without sacrificing detail, we used point neurons to simulate the remaining neuronal types. GCs major input from the Entorhinal Cortex (EC) is simulated as independent poisson spike trains at realistic firing frequencies. The output of the network corresponds to the spiking activity of GCs and is estimated on two highly overlapping input patterns. Pattern separation is accomplished when the similarity between these input patterns is greater than the similarity between the respective output patterns, as assessed by the Hamming Distance (HD) metric. Preliminary results show that there is a positive correlation between the separation efficiency and the number of GC dendrites. Conclusions: Our preliminary results suggest that dendrites of GC cells facilitate the pattern separation capabilities of the DG.

scholarly journals Dendrites of DG granule cells contribute to pattern separation by controlling sparsity

2016 ◽  
Author(s):  
Spyridon Chavlis ◽  
Panagiotis C. Petrantonakis ◽  
Panayiota Poirazi
Keyword(s):  
Dentate Gyrus ◽  
Computational Model ◽  
Granule Cells ◽  
Separation Efficiency ◽  
Pattern Separation ◽  
Biologically Relevant ◽  
Incoming Information ◽  
And Performance ◽  
Dendritic Atrophy

AbstractThe hippocampus plays a key role in pattern separation, the process of transforming similar incoming information to highly dissimilar, non-overlapping representations. Sparse firing granule cells (GCs) in the dentate gyrus (DG) have been proposed to undertake this computation, but little is known about which of their properties influence pattern separation. Dendritic atrophy has been reported in diseases associated with pattern separation deficits, suggesting a possible role for dendrites in this phenomenon. To investigate whether and how the dendrites of GCs contribute to pattern separation, we build a simplified, biologically relevant, computational model of the DG. Our model suggests that the presence of GC dendrites is associated with high pattern separation efficiency while their atrophy leads to increased excitability and performance impairments. These impairments can be rescued by restoring GC sparsity to control levels through various manipulations. We predict that dendrites contribute to pattern separation as a mechanism for controlling sparsity.

Interactions of Excitatory and Inhibitory Feedback Topologies in Facilitating Pattern Separation and Retrieval

2012 ◽  
Vol 24 (1) ◽  
pp. 32-59
Author(s):  
Jane X. Wang ◽  
Michal Zochowski
Keyword(s):  
Memory Management ◽  
Activity Patterns ◽  
Pattern Separation ◽  
Memory Recall ◽  
Cognitive States ◽  
Management Processes ◽  
Inhibitory Feedback ◽  
Global And Local ◽  
The Brain

Within the brain, the interplay between connectivity patterns of neurons and their spatiotemporal dynamics is believed to be intricately linked to the bases of behavior, such as the process of storing, consolidating, and retrieving memory traces. Memory is believed to be stored in the synaptic patterns of anatomical circuitry in the form of increased connectivity densities within subpopulations of neurons. At the same time, memory recall is thought to correspond to activation of discrete areas of the brain corresponding to those memories. Such regional subpopulations can selectively activate during memory recall or retrieval, signifying the process of accessing a single memory or concept. It has been shown previously that recovery of single memory activity patterns is mediated by global neuromodulation signifying transition into different cognitive states such as sleep or awake exploration. We examine how underlying topology can affect memory awake activation and sleep reactivation when such memories share increasing proportions of neurons. The results show that while single memory activation is diminished with increased overlap, pattern separation can be recovered by offsetting excitatory associations between two memories with targeted and heterogeneous inhibitory feedback. Such findings point to the importance of excitatory-to-inhibitory current balance at both the global and local levels in the context of memory retrieval and replay, and highlight the role of network topology in memory management processes.

scholarly journals Dentate Gyrus Somatostatin Cells are Required for Contextual Discrimination During Episodic Memory Encoding

2020 ◽  
Author(s):  
Cristian Morales ◽  
Juan Facundo Morici ◽  
Nelson Espinosa ◽  
Agostina Sacson ◽  
Ariel Lara-Vasquez ◽  
...  
Keyword(s):  
Episodic Memory ◽  
Dentate Gyrus ◽  
Granule Cells ◽  
Memory Systems ◽  
Pattern Separation ◽  
Activity Levels ◽  
Connection Probability ◽  
Somatostatin Cells ◽  
Formation Pattern

Abstract Memory systems ought to store and discriminate representations of similar experiences in order to efficiently guide future decisions. This problem is solved by pattern separation, implemented in the dentate gyrus (DG) by granule cells to support episodic memory formation. Pattern separation is enabled by tonic inhibitory bombardment generated by multiple GABAergic cell populations that strictly maintain low activity levels in granule cells. Somatostatin-expressing cells are one of those interneuron populations, selectively targeting the distal dendrites of granule cells, where cortical multimodal information reaches the DG. Nonetheless, somatostatin cells have very low connection probability and synaptic efficacy with both granule cells and other interneuron types. Hence, the role of somatostatin cells in DG circuitry, particularly in the context of pattern separation, remains uncertain. Here, by using optogenetic stimulation and behavioral tasks in mice, we demonstrate that somatostatin cells are required for the acquisition of both contextual and spatial overlapping memories.

scholarly journals Adult hippocampal neurogenesis shapes adaptation and improves stress response: a mechanistic and integrative perspective

2021 ◽  
Author(s):  
A. Surget ◽  
C. Belzung
Keyword(s):  
Stress Response ◽  
Hippocampal Neurogenesis ◽  
Adult Hippocampal Neurogenesis ◽  
Pattern Separation ◽  
Brain Areas ◽  
Functional Involvement ◽  
Different Dimensions ◽  
Stressful Experiences ◽  
The Brain

AbstractAdult hippocampal neurogenesis (AHN) represents a remarkable form of neuroplasticity that has increasingly been linked to the stress response in recent years. However, the hippocampus does not itself support the expression of the different dimensions of the stress response. Moreover, the main hippocampal functions are essentially preserved under AHN depletion and adult-born immature neurons (abGNs) have no extrahippocampal projections, which questions the mechanisms by which abGNs influence functions supported by brain areas far from the hippocampus. Within this framework, we propose that through its computational influences AHN is pivotal in shaping adaption to environmental demands, underlying its role in stress response. The hippocampus with its high input convergence and output divergence represents a computational hub, ideally positioned in the brain (1) to detect cues and contexts linked to past, current and predicted stressful experiences, and (2) to supervise the expression of the stress response at the cognitive, affective, behavioral, and physiological levels. AHN appears to bias hippocampal computations toward enhanced conjunctive encoding and pattern separation, promoting contextual discrimination and cognitive flexibility, reducing proactive interference and generalization of stressful experiences to safe contexts. These effects result in gating downstream brain areas with more accurate and contextualized information, enabling the different dimensions of the stress response to be more appropriately set with specific contexts. Here, we first provide an integrative perspective of the functional involvement of AHN in the hippocampus and a phenomenological overview of the stress response. We then examine the mechanistic underpinning of the role of AHN in the stress response and describe its potential implications in the different dimensions accompanying this response.

scholarly journals The role of piriform associative connections in odor categorization

eLife ◽  
2016 ◽  
Vol 5 ◽  
Author(s):  
Xiaojun Bao ◽  
Louise LG Raguet ◽  
Sydni M Cole ◽  
James D Howard ◽  
Jay A Gottfried
Keyword(s):  
Activity Patterns ◽  
Piriform Cortex ◽  
Discrimination Performance ◽  
Object Identification ◽  
Pattern Separation ◽  
Odor Perception ◽  
Drug Induced ◽  
Multivariate Pattern ◽  
The Brain

Distributed neural activity patterns are widely proposed to underlie object identification and categorization in the brain. In the olfactory domain, pattern-based representations of odor objects are encoded in piriform cortex. This region receives both afferent and associative inputs, though their relative contributions to odor perception are poorly understood. Here, we combined a placebo-controlled pharmacological fMRI paradigm with multivariate pattern analyses to test the role of associative connections in sustaining olfactory categorical representations. Administration of baclofen, a GABA(B) agonist known to attenuate piriform associative inputs, interfered with within-category pattern separation in piriform cortex, and the magnitude of this drug-induced change predicted perceptual alterations in fine-odor discrimination performance. Comparatively, baclofen reduced pattern separation between odor categories in orbitofrontal cortex, and impeded within-category generalization in hippocampus. Our findings suggest that odor categorization is a dynamic process concurrently engaging stimulus discrimination and generalization at different stages of olfactory information processing, and highlight the importance of associative networks in maintaining categorical boundaries.

scholarly journals The Continuity of Context: A Role for the Hippocampus

2020 ◽  
Author(s):  
Andrew Maurer ◽  
Lynn Nadel
Keyword(s):  
Stimulus Equivalence ◽  
Multiple Scales ◽  
Critical Role ◽  
Longitudinal Axis ◽  
Place Cells ◽  
Pattern Separation ◽  
Anatomy And Physiology ◽  
The Brain ◽  
Over Time

Tracking moment-to-moment change in input, and detecting change sufficient to require altering behavior is crucial to survival. We discuss how the brain evaluates change over time, focusing on hippocampus and its role in tracking context. We leverage the anatomy and physiology of the hippocampal longitudinal axis, re-entrant loops, and amorphous networks, to account for stimulus equivalence and the updating of an organism’s sense of its context. Place cells play a central role in tracking contextual continuities and discontinuities across multiple scales, a capacity beyond current models of pattern separation and completion. This perspective highlights the critical role of the hippocampus in both spatial cognition and episodic memory: tracking change and detecting boundaries separating one context, or episode, from another.

scholarly journals CXCR7 regulates epileptic seizures by controlling the synaptic activity of hippocampal granule cells

2019 ◽  
Vol 10 (11) ◽  
Author(s):  
Tao Xu ◽  
Xinyuan Yu ◽  
Jing Deng ◽  
Shu Ou ◽  
Xi Liu ◽  
...  
Keyword(s):  
Granule Cells ◽  
Epileptic Seizures ◽  
Synaptic Activity ◽  
Membrane Expression ◽  
Extracellular Signal Regulated Kinase ◽  
Extracellular Signal ◽  
Synaptic Neurotransmission ◽  
Novel Target ◽  
The Brain

Abstract C–X–C motif chemokine receptor 7 (CXCR7), which mediates the immune response in the brain, was recently reported to regulate neurological functions. However, the role of CXCR7 in epilepsy remains unclear. Here, we found that CXCR7 was upregulated in the hippocampal dentate gyrus (DG) of mice subjected to kainic acid (KA)-induced epilepsy and in the brain tissues of patients with temporal lobe epilepsy. Silencing CXCR7 in the hippocampal DG region exerted an antiepileptic effect on the KA-induced mouse model of epilepsy, whereas CXCR7 overexpression produced a seizure-aggravating effect. Mechanistically, CXCR7 selectively regulated N-methyl-d-aspartate receptor (NMDAR)-mediated synaptic neurotransmission in hippocampal dentate granule cells by modulating the cell membrane expression of the NMDAR subunit2A, which requires the activation of extracellular signal-regulated kinase 1/2 (ERK1/2). Thus, CXCR7 may regulate epileptic seizures and represents a novel target for antiepileptic treatments.

The Role of Mitochondria in the Genesis of Neuroaxonal Dystrophy in the Brains of Aging Mice

1975 ◽  
Vol 33 ◽  
pp. 372-373
Author(s):  
J.E. Johnson
Keyword(s):  
Electron Microscopy ◽  
Present Report ◽  
Light And Electron Microscopy ◽  
Dorsal Column ◽  
Neuroaxonal Dystrophy ◽  
Nucleus Gracilis ◽  
Dystrophic Axons ◽  
The Brain ◽  
Nucleus Cuneatus

Although neuroaxonal dystrophy (NAD) has been examined by light and electron microscopy for years, the nature of the components in the dystrophic axons is not well understood. The present report examines nucleus gracilis and cuneatus (the dorsal column nuclei) in the brain stem of aging mice.Mice (C57BL/6J) were sacrificed by aldehyde perfusion at ages ranging from 3 months to 23 months. Several brain areas and parts of other organs were processed for electron microscopy.At 3 months of age, very little evidence of NAD can be discerned by light microscopy. At the EM level, a few axons are found to contain dystrophic material. By 23 months of age, the entire nucleus gracilis is filled with dystrophic axons. Much less NAD is seen in nucleus cuneatus by comparison. The most recurrent pattern of NAD is an enlarged profile, in the center of which is a mass of reticulated material (reticulated portion; or RP).

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