Memory encoding

The hippocampus plays a central role in memory processing. In order to avoid deleterious interference between stored and ongoing experience, theoretical considerations require a separation between phases of memory encoding and recall within the same neural circuit, putatively controlled by hippocampal theta oscillations [1]. However, the neural mechanisms subserving this separation remain unknown. Classical models either remain moot about these mechanisms [2], or assume purpose-built neuromodulatory interactions that are in conflict with biologically realistic timescales of synaptic modulation

The hippocampus is essential for spatial navigation and memory processes. Hippocampal pyramidal cells (PCs) often exhibit complex spike bursts (CSBs) that are driven by regenerative dendritic Ca2+ plateau potentials. These events can induce rapid synaptic plasticity and new place field (PF) formation in CA1PCs. CA3PCs also fire CSBs, and their PF-inducing CSBs were shown to be particularly prolonged (Li et al, bioRxiv). However, the dendritic mechanisms underlying such long-lasting events in CA3PCs remain unclear. In acute rat brain slices, we observed large heterogeneity among CA3PCs in CSB p

Understanding memory encoding and recall processes in the hippocampus is pivotal for unravelling brain function. We employed two-photon calcium imaging to observe neuronal activity (hippocampal CA1 neurons) in behaving mice performing spatial memory tasks, capturing the dynamics of memory-related circuits. Shannon Information Theory provides a useful toolbox, applicable to the analysis of calcium imaging datasets, to assay changes in information representation and processing in brain circuits while mice are performing such cognitive tasks. In particular, the recently developed Partial Informat

The encoding or retrieval of a contextual fear memory recruits the activity of thousands of neurons across the mammalian brain. This ensemble of cells is often identified by immediate-early genes (IEGs), which are expressed following neuronal activity, but the extent to which the expression pattern of one IEG reflects another is unclear. Here, we examined the IEGs Arc/Arg3.1 and c-Fos across several brain regions during fear memory encoding or retrieval. Mice were administered a 3-shock contextual fear conditioning (CFC) paradigm and sacrificed 1h later (encoding), 1 h after context re-exposur

…In particular, encoding and recall of memory induces bursts of HFOs at distinct frequency and latency depending on the cortical location. How these local neural assembly activities are globally coordinated across the brain during memory processing remains elusive. Intracranial local field potential recordings from epilepsy patients were used to detect individual

Studying the neural mechanisms of encoding new memories is crucial for understanding and restoring cognitive function. In this study, we utilized functional connectivity metrics to identify hubs responsible for successful or unsuccessful encoding in a free recall task among eleven epileptic patients undergoing stereo EEG presurgical evaluation. Firstly, several types of functional connectivity metrics were calculated across standard EEG bands, ripples, and fast ripples for each patient, feature, encoded word and time window across all possible pairs of contacts. Whole-brain connectivity maps w

…activities such as navigation and memory encoding in a more natural way that

The dentate gyrus (DG) plays a key role in memory encoding and retrieval, facilitating discrimination of the environmental inputs by separating them into non-overlapping patterns and reducing interference of stored representations. It is highly susceptible to aging-related structural and physiological changes and thought to contribute to age-related cognitive dysfunctions. In this study we examined possible age-related changes in pattern separation function and associated changes in DG cellular engrams using a contextual fear conditioning task. Young adult (3-month-old) and healthy aged (24-mo

The hippocampus is known to play a major role in the storage and recall of information depending on various forms of activity dependent synaptic plasticity. Mossy fiber synapses between the axons of dentate gyrus (DG) granule cells and CA3 pyramidal cells (Mf-CA3 synapses) display a high dynamic range of presynaptic plasticity which endow these synaptic connections with detonator properties. The pattern of action potential firing, in the form of high frequency bursts in the DG, strongly controls the amplitude of synaptic responses and information transfer to CA3. Presynaptic short-term plastic

To understand how amyloidosis in Alzheimer’s Disease changes circuit properties affecting memory encoding and recall, we examined the relationship between neuronal activity, nearness to amyloid plaques, and spatial memory readout from hippocampal CA1 place cells. We performed two-photon calcium imaging in head-fixed 5xFAD mice navigating an air-lifted circular track. Neuronal hyperactivity in CA1 during non-running periods was higher in 5xFAD mice compared to wildtype littermates in both young (2-3 months) and old (6.5-10 months) groups. Moreover, neurons close to amyloid plaques (<20µm in

The hippocampal CA3-CA1 circuit is critical for memory encoding and retrieval. Previous work has shown this feedforward excitatory-inhibitory network (FFEI) maintains a precise excitation-inhibition (E-I) balance onto CA1 pyramidal cells (CA1PCs) (Bhatia et al, 2019). However, how this balance dynamically evolves dependent of the history of sustained input activity is unclear. Deviations from E-I balance are important for gating, normalization, and representation of input ensembles. Using in vitro whole-cell recordings in mouse hippocampal slices, we probed E-I balance by optogenetically evok

…the neural circuitry modulating fear memory could be the turning point for the comprehension of this emotion and its pathological states. A comprehensive understanding of the circuits mediating memory encoding, consolidation, and retrieval presents the fundamental technological challenge of analyzing activity in the entire brain with single-neuron resolution. In this context, we develop the brain-wide neuron quantification toolkit (BRANT) for mapping whole-brain neuronal activati

It has long been established that the hippocampus plays a crucial role for episodic memory. As opposed to the modular approach, now it is generally assumed that being a complex structure, the HC performs multiplex interconnected functions, whose hierarchical organization provides basis for the higher cognitive functions such as semantics-based encoding and retrieval. However, the «where, when and how» properties of distinct memory aspects within and outside the HC are still under debate. Here we used a visual associative memory task as a probe to test the hypothesis about the differential invo

A central problem in neuroscience is to understand how areas in the brain communicate. Inputs to brain areas largely influence the intrinsic dynamics of each region, which shapes ongoing computations. Hence, characterizing how inputs drive different population responses is key to understanding how brain circuits are controlled to generate different behaviors. To this end, we developed an inter-areal patterned microstimulation (uStim) protocol that allowed us to finely manipulate the activity of a neural population in one brain area while simultaneously recording the activity of a second popula

…mechanistic explanation of how working memory (WM) representations are built from the latent representations of visual knowledge and can then be reconstructed. The proposed model, Memory for Latent Representations (MLR), features a variational autoencoder with an architecture that corresponds broadly to the human visual system and an activation-based binding pool of neurons that binds items’ attributes to tokenized representations. The simulation r

…regardless of an individual’s actual memory for that item. In this talk, Dr. Bainbridge will discuss our current neuroscientific understanding of how memorability is represented in patterns in the brain, potentially serving as a signal for how stimulus informat