Place fields

Behavioral time scale synaptic plasticity underlies CA1 place fields

…drive the formation of hippocampal fields such as place fields. BTSP differentiates itself from typical forms of plasticity by a) learning pre-post correlations on the timescales of seconds and b) learning in a one-to-few-shot manner. Though BTSP has been posited to be the primary driver of field formation in hippocampus, theoretical models that describe the population-level computations of hippocampus (such as the formation of "cognitive" or "

When rodents learn to navigate in a new environment, high place field density emerge at reward locations, fields elongate against the trajectory, and individual fields change spatial selectivity or drift while demonstrating stable behavior. Why place fields demonstrate these characteristic phenomena during learning remains elusive. We develop a model that optimizes for a normative goal, which is to maximize cumulative rewards. Place fields are modelled using Gaussian basis functions to represent spatial information of an environment, and directly synapse to an actor-critic for policy learning

…Place cells, specialised neurons residing within the hippocampus, exhibit selective firing patterns corresponding to specific spatial locations, collectively contributing to the cognitive mapping of the environment. In healthy state, the place fields in the CA1 region exhibits continuous representational turnover [1]. Spatial navigation is disrupted in Alzheimer’s Disease (AD). AD, a neurodegenerative disorder characterised by progressive cognitive decline, is associated with deficits in learning a

Creating place fields in place cells is crucial for forming spatially dependent episodic memories in the brain, with the hippocampus playing a central role. Specifically, we focus on CA1 pyramidal neurons, which receive inputs from the CA3 and entorhinal cortex (EC). No widely accepted network-based theory for place field formation exists, but many models offer mechanisms for place-field firing. One type of hypotheses proposes that it results from summated output of spatially tuned cells, like grid cells or boundary vector cells. Another suggests CA1 place fields are replicate of CA3 place fie

Hippocampal place cell populations putatively encode allocentric spatial position [1-4]. In bats and rodents, place cells exhibit heterogeneously sized and overlapping receptive (or place) fields [5-9]. These heterogeneous place fields instantiate a multiscale spatial tuning landscape in which the larger place fields of some place cells encompass the relatively more numerous narrowly tuned place fields of other cells (Fig 1a). In this work, we investigate the effectiveness of such multiscale codes for encoding allocentric spatial position. We do so by deriving closed-form expressions for how w

…which display spatially tuned firing (place cells). When an animal enters a novel environment, new spatially tuned firing (place fields: PFs) of PCs emerges. Place field formation in CA1 PCs has been proposed to rely on a well-established cellular mechanism called behavioural timescale synaptic plasticity (BTSP). During BTSP, a single occurrence of a long postsynaptic dendritic plateau potential and resulti

Hippocampal pyramidal cells (PCs) express spatially tuned activity (i.e., ‘place cells’ exhibiting ‘place fields’, PF) to support navigation. However, the cellular mechanisms of novel PF formation are elusive. Behavioral time scale synaptic plasticity (BTSP), recently described in mouse CA1PCs, is a putative mechanism of PF formation (Bittner et al., 2015). It starts with a silent PC exhibiting a large Ca2+ plateau in dendrites accompanied by somatic bursting, which initiates the emergence of tuning near the location of induction. Consequently, activity is strongest during formation and lower

The dentate gyrus (DG) plays a key role in the emergence of spatial and contextual map representation within the hippocampus during learning. Granule cells (GCs) of the DG receive their major spatial cortical input from the medial entorhinal cortex (MEC) via the perforant path. To determine whether inputs from the MEC (in particular layer II stellate cells) play a role in the capacity of the DG to differentiate between different environments, we aim to modulate their activity using DREADDs. Thanks to these pharmacogenetic tools, we can de- or hyper-polarize MEC-layer II stellate cells during e

During spatial navigation, hippocampal place cells rely on visual inputs to map space, but other sensory modalities, such as odour, can also be effectively used (doi: 10.1093/cercor/bht239). Although rodents are nocturnal and short-sighted, little is known about the role of other sensory modalities as substrates for place fields. Here, we recorded electrophysiologically from place cells in the hippocampal CA1 region of adult male rats while they explored a round empty field arena in darkness and in the absence of reliable tactile, olfactory, and visual cues. We compared place cell behaviour un

While the hippocampus is known to encode physical position through place cells, substantial evidence indicates that hippocampal neurons also respond to a variety of other non-spatial sensory information. We explore the hypothesis that these representations emerge through generic computations implemented by the hippocampus that actively learn from the statistical structure of experience. Theoretical work has shown that place cell coding arises as a special case during spatial exploration in networks trained to learn sparse, compressed representations, due to the local correlations present in th

…neurons fire in localised receptive fields that tile an animal's physical environment, forming a sparse spatial population code. But the underlying computations and their functional purpose remain unclear. Various ANNs have been proposed to learn localised, manifold-tiling codes, purportedly due to explicit constraints on network activity levels or to specific task objectives, such as predicting future observations. Here, we show that in si

The hippocampus is a key player in learning and memory. Research into this brain structure has long emphasized its plasticity and flexibility, though recent reports have come to appreciate its remarkably stable firing patterns. How novel information incorporates itself into networks that maintain their ongoing dynamics remains an open question, largely due to a lack of experimental access points into network stability. Development may provide one such access point. To explore this hypothesis, we birthdated CA1 pyramidal neurons using in-utero electroporation and examined their functional featu

…because of the inaccessibility of place fields when animals are not actively exploring a maze. Here, we devised a novel Bayesian learning approach based on the spike-triggered average decoded position in ensemble recordings to track dynamically the spatial tuning of individual neurons during offline states in freely moving rats. Measuring these dynamic tunings, we found spatial representations within

…different brain states and overlapping place tuning during behavior (Author et al.,

…spatial modulation of their activity (place fields) lap by lap. During exploration of a novel environment, 50

A key issue in understanding circuit operations is the extent to which neuronal spiking reflects local computation or responses to upstream inputs. Several studies have lesioned or silenced inputs to area CA1 of the hippocampus - either area CA3 or the entorhinal cortex and examined the effect on CA1 pyramidal cells. However, the types of the reported physiological impairments vary widely, primarily because simultaneous manipulations of these redundant inputs have never been performed. In this study, I combined optogenetic silencing of unilateral and bilateral mEC, of the local CA1 region, and

Two aspects of hippocampal temporal coding during behaviour have come to dominate theories of hippocampal function: phase precession at the single-cell level, and theta sequences at the population level. Both their significance for memory functions as much as their connection to specific network dynamics and to each other, remain matter for speculation. Here we address these questions by taking advantage of simultaneous recordings of population activity and layer-specific LFP dynamics in the CA1 region. What we find is that these two phenomena are largely segregated both at the spatial and at

…whether the precise spatial tuning of place cells as a function of animal position is preserved as a function of encoded replay position, independent of the animal's location. This is far from obviou

…and maintenance of hippocampal place codes. It is unclear, however, which properties of these neural codes are inherited from upstream processing and which are learned through plasticity. To disentangle these influences on place codes, we utilized a method for abolishing LTP specifically in hippocampal region CA1 of the adult mouse without affecting basal synaptic processing: conditional genetic deletion of a necessary component of the postsynaptic membrane fusion machinery, Syntaxin3 (Stx3). Surp