Hippocampal formation

The hippocampal formation is a crucial region in the encoding and retrieval of memory, thought to be mediated through ensemble formation and recruitment or intrinsic attractor dynamics. Additionally, it has been shown that overall hippocampal population activity reflects environmental novelty. However, a common neural basis supporting these two processes remains unknown. Furthermore, many memories contain overlapping features, and it remains to be established how specific memories are retrieved without interference in the hippocampus. We propose that both engram and attractor models hinge on l

Hippocampal remapping describes the phenomenon of substantial reshuffling of the spatial preferences of hippocampal place cells in response to environmental changes. Disparate neural representations in different environments could reduce interference between competing memories, hence functionally supporting robust context-dependent spatial cognition. Experimental data on existing remapping studies exhibit a diverse range of physiological properties, sometimes with seemingly conflicting results. In particular, subtle changes in experimental conditions lead to qualitatively different results. De

There has been a long-lasting debate on whether the function of the hippocampal formation is to store and retrieve episodic memory, supported by experiments in humans, or to code for space, suggested by spatially tuned cells (place cells, grid cells, etc.) recorded in nonhuman animals. In an attempt to reconcile the two views, we use a memory-augmented neural network in a reinforcement learning setup to solve a navigation task in a simulated maze. The key feature of the model is that it learns autonomously what and when to store into, and retrieve from, an external memory buffer. Once the mode

The hippocampal formation plays a key role in learning and memory, with CA3 thought to be the substrate of pattern completion [1]. However, its underlying computational and synaptic mechanisms are not yet understood. Here we analyze the mechanisms behind sequence replay through simulations of spiking neurons and a time-discrete model of moving membrane potential distributions. First, we simulated spiking networks of excitatory leaky integrate-and-fire cells forming a sequence of assemblies. The sequence contains both recurrent and feedforward connections (within and across assemblies, respect

…sleep and awake immobility in the hippocampal formation of most mammals [Buzsáki, 2015]. During SPW-Rs behavioral sequences are replayed compressed in time [Wilson & McNaughton, 1994; Diba & Buzsáki, 2007], which led to the hypothesis that they are mediating memory transfer from the hippocampus to the neocortex [Buzsáki, 1989]. SPW-Rs can be internally generated in the highly recurrent CA3 network [Maier et al., 2003], but their incidence during sleep is affected by slow oscillations in the cortex [Sirota et al

Alzheimer's disease (AD), the most common neurodegenerative dementia, involves Presenilins (PS) 1 and 2, which are pivotal in amyloid-β (Aβ) production and amyloid pathology. PS functions, associated with inherited AD (FAD), extend beyond Aβ production. PS2 in particular is critical in mitochondrial function and cell bioenergetics. Here, we aim to explore Presenilins' role in cellular lipid metabolism.Brain samples were collected from WT, PS2 +/-, PS2 -/- and PS2N141I mice, carrying the FAD N141I mutation. We evaluated LPL and nSMase 2 levels based on preliminary data indicating their upregula

…medially located structure within the hippocampal formation, remains understudied. In order to gain insight into the unique features and potential functions of the FC, we examined the morphology, physiology, and connectivity of its principal neurons in anesthetized mice. Using in-vivo single-cell juxtacellular recording-labeling and quantitative morphometric analysis, we found that FC neurons exhibit unique firing patterns and dendritic architectures, which are distinct from principal cell po

…association of sleep-wake states with hippocampal rhythms, the mutual influence of the hippocampal formation in regulating vigilance states has been largely neglected. Here, we focus on the subiculum, the main outp

…The hippocampal formation constructs a spatial cognitive map using spatial cells like Place, Grid, and Head Direction cells. Sensory processing guides this map's construction, with the Medial Entorhinal Cortex (MEC) encoding self-motion cues (Path Integration) analogous to the 'where' pathway, while the Lateral Entorhinal Cortex (LEC) integrates sensory inputs analogous to the 'what' pathway. Object-dependent spatial cells, including Object Vector cells, Object Sensitive

Abundant work has highlighted the functional role of the hippocampal formation in navigation behaviour across species. Recent studies highlight evidence that the same neural coding mechanisms found to underly the representation of physical spaces also apply to conceptual domains. Specifically, the representation of locations in both physical and conceptual spaces is reflected in distinct neural activity patterns in hippocampus and entorhinal cortex. Electrophysiological work from rodents has shown that single hippocampal place cells represent different locations in different spaces – a functio

The subiculum is one of the most important brain structure in the hippocampal formation which has an essential role in forwarding the hippocampal information to different cortical and subcortical regions. Pyramidal cells are the principal cell type in the subiculum and based on their firing dynamics, they can be divided into regular and bursting phenotypes. Previously, functional characterization of these cells was mainly performed by using conventional electrophysiological methods (current steps). However, our research group uses advanced methods (dynamic clamp) to expose neurons to physiolog

The hippocampal formation is important for encoding, consolidation and retrieval of episodic memories. While integration of spatial information into episodic memories has been studied in great detail, how social information is encoded in the brain has received less attention. Emerging evidence suggests that the hippocampus area CA2 plays an essential role for social recognition memories, and previous studies show that silencing area CA2 impairs social recognition in mice. To determine how social, spatial and object information is computed in the different areas of the hippocampus, we recorded

Over the past decades, the hippocampal formation has undergoneextensive study leading researchers to identify a vast array ofcells with functional properties (place cells, splitter cells,etc). In the present work, we aim at investigating whether theactivity of those cells derive from the anatomy of the hippocampalformation and the properties of neuron or derive instead from theactual behavior of the animal. To do so, we simulated an agentnavigating inside an 8-shaped track, making alternating choices(T-maze alternating task). We designed a random network, based onthe reservoir computing paradi

Deep Brain Stimulation (DBS) of the hippocampal formation is currently investigated as a therapeutic approach for the treatment of memory disorders and epilepsy. Although various neurostimulation protocols have been extensively studied semi-acutely in epileptic patients, their refinement requires more standardized preclinical testing in non-human primates (NHP). However, targeting deep brain structures such as the hippocampal formation in NHP still remains a challenging task. Here, we present a technological framework for submillimeter targeting of the hippocampal formation in macaque monkeys

…to model representations in the hippocampal formation. I will introduce a tractable implementation of a predictive map called the successor representation (SR), before presenting data showing that rats and humans display SR-like navigational choices on a novel open-field maze. Next, I will show how such a predictive map could be implemented using spatial representations found in the hippocampal formation, before finally presenting how such learning might be well approximated by phenomena that exist in the spatial memory system - name

…maps, that are associated with the hippocampal formation and are similar to world-centered representations of the environment, and image spaces, that are associated with the parietal cortex and are similar to self-centered spatial relationships. I will suggest that cognitive maps and image spaces may be two manifestations of a m

There is a long-standing tension between the notion that the hippocampal formation is essentially a spatial mapping system, and the notion that it plays an essential role in the establishment of episodic memory and the consolidation of such memory into structured knowledge about the world. One theory that resolves this tension is the notion that the hippocampus generates rather arbitrary 'index' codes that serve initially to link attributes of episodic memories that are stored in widely dispersed and only weakly connected neocortical modules. I will show how an essentially 'spatial' coding mec