Topic: memory consolidation

Much is known about the neural representations of current environmental location and direction within the hippocampal formation, but use of such a “cognitive map” requires the online representation of desired locations and how to get there, and the neural basis for this function has been more elusive. I will discuss how “theta sweeps” of place and grid cell firing encode the current location (at early phases of each theta cycle) while, at later phases, sampling around the forward direction during exploration and indicating the direction to desired locations during goal-directed navigation. I w

Cancer-related fatigue is a prominent and debilitating side effect of cancer and its treatment. It can develop prior to diagnosis, generally peaks during cancer treatment, and can persist long after treatment completion. Its mechanisms are multifactorial, and its expression is highly variable. Unfortunately, treatment options are limited. Our research uses syngeneic murine models of cancer and cisplatin-based chemotherapy to better understand these mechanisms. Our data indicate that both peripherally and centrally processes may contribute to the developmental of fatigue. These processes includ

Experiences are encoded in sparse neuronal ensembles that can be defined by the transcription activation of immediate-early genes such as Fos and Npas4. The Fos+ and Npas4+ neuronal ensembles within an engram have been reported to recruit distinct synaptic plasticity mechanisms. However, it remains unknown whether and how Fos- and Npas4-mediated synaptic plasticity support memory consolidation. Here we provide experimental and computational evidence that Fos+ and Npas4+ neuronal ensembles coordinate different excitatory and inhibitory synaptic plasticity mechanisms to promote memory consolidat

Memory consolidation is the process by which recent experiences are assimilated into long-term memory. In animals, this process requires the offline replay of sequences observed during online exploration in the hippocampus. Recent experimental work has found that salient but task-irrelevant stimuli are systematically excluded from these replay epochs, suggesting that replay samples from an abstracted model of the world, rather than verbatim previous experiences. We find that this phenomenon can be explained parsimoniously and biologically plausibly by a Hebbian spike time-dependent plasticity

Episodic memories are encoded by sparse populations of neurons activated during an experience. These neural ensembles constitute memory engrams that are both necessary and sufficient for inducing recall even long after memory acquisition. This suggests that following encoding, engrams are stabilized to support reliable memory retrieval. However, little is known about the temporal evolution of engrams over the course of memory consolidation or how it impacts mnemonic properties. Here we employed computational and experimental approaches to examine how the composition and selectivity of engrams

Hippocampal ripple oscillations (140–220 Hz) have been implicated in important cognitive functions such as memory consolidation (Buzsáki 1989). Their generating mechanism however remains unclear, although various models have been proposed. We suggest that transient features of ripples can guide model selection: So far only the “bifurcation-based” inhibitory network model (Donoso et al. 2018, Brunel and Hakim 1999) could reproduce the experimentally observed intra-ripple frequency accommodation (IFA) — an asymmetry in the instantaneous ripple frequency in response to transient, sharp wave-like

The brain is a prediction machine. Yet the world is never entirely predictable, for any animal. Unexpected events are surprising and this typically evokes prediction error signatures in animal brains. In humans such mismatched expectations are often associated with an emotional response as well. Appropriate emotional responses are understood to be important for memory consolidation, suggesting that valence cues more generally constitute an ancient mechanism designed to potently refine and generalize internal models of the world and thereby minimize prediction errors. On the other hand, abolish

New memories are initially labile and have to be consolidated into stable long-term representations. Current theories assume that this is supported by a shift in the neural substrate that supports the memory, away from rapidly plastic hippocampal networks towards more stable representations in the neocortex. Rehearsal, i.e. repeated activation of the neural circuits that store a memory, is thought to crucially contribute to the formation of neocortical long-term memory representations. This may either be achieved by repeated study during wakefulness or by a covert reactivation of memory traces

The hippocampus and the amygdala are two structures required for emotional memory. While the hippocampus encodes the contextual part of the memory, the amygdala processes its emotional valence. During Non-REM sleep, the hippocampus displays high frequency oscillations called “ripples”. Our early work shows that the suppression of ripples during sleep impairs performance on a spatial task, underlying their crucial role in memory consolidation. We more recently showed that the joint amygdala-hippocampus activity linked to aversive learning is reinstated during the following Non-REM sleep epochs,

Neocortical-hippocampal interactions during off-line periods such as slow-wave sleep are implicated in memory processing. In particular, recent memory traces are replayed in hippocampus during some sharp-wave ripple (SWR) events, and these replay events are positively correlated with neocortical memory trace reactivation. A prevalent model is that SWR arise ‘spontaneously’ in CA3 and propagate recent memory ‘indices’ outward to the neocortex to enable memory consolidation there; however, the spatiotemporal distribution of neocortical activation relative to SWR is incompletely understood. We us

50 years ago it was found that sleep somehow made memories better and more permanent, but neither sleep nor memory researchers knew enough about sleep and memory to devise robust, effective tests. Today the fields of sleep and memory have grown and what is now understood is astounding. Still, great mysteries remain. What is the functional difference between the subtly different slow oscillation vs the slow wave of sleep and do they really have opposite memory consolidation effects? How do short spindles (e.g. <0.5 s as in schizophrenia) differ in function from longer ones and are longer spindl

Accumulating evidence from electrocorticogram (ECoG) recordings and imaging challenge traditional views of brain oscillations as spatially stationary periodic sources. Understanding the spatio-temporal dynamics of cortical activity requires novel measurement and analysis methodologies. We recorded broadband local field potential (LFP) across the whole neocortex in freely behaving rats using high-density flexible surface arrays using active transistors. 3D tracking and spatio-spectral analysis of recordings over long sessions enabled automatic and accurate brain and behavioral states segmentati

Sharp-wave ripples (SWRs) are thought to play a crucial role in memory consolidation, learning, and the formation of long-term memories by facilitating the transfer of information from the hippocampus to neocortical networks. To understand the mechanisms governing SWRs, we have developed a closed-loop stimulation framework tailored for the real-time detection and suppression of SWRs, leveraging the ONIX electrophysiology acquisition system and BONSAI-RX acquisition software. As part of our Bonsai package, we developed a convolutional neural network (CNN) for detection of SWRs recorded with lam

Neural replay, a phenomenon where activation sequences experienced during wakefulness are replayed during rest or sleep, is thought to play a crucial role in memory consolidation and planning [1]. It is commonly modeled as a chain of activity, where links are formed based on temporal associations in the stimulus. Existing work [2,3] focuses on simple patterns, yet we know that the brain is capable of learning complex spatiotemporal dynamics. Specifically chaotic dynamics are even challenging for conventional deep learning algorithms due to exploding gradients. We demonstrate that by introducin

Neural events are characteristic transient, coordinated neural activities observable in the brain’s aggregate signals, such as local field potentials (LFPs). It was shown that certain neural events, like sharp wave-ripples (SWR) [1], play a crucial role in various cognitive functions, including memory consolidation and both offline and online planning. These events have signatures across nearly all scales, from microscopic coordination at the level of individual spiking activity and synaptic dynamics [2] to macroscopic regulation in the thalamocortical system [3]. Despite the growing recogniti