Fear learning induces synaptic potentiation between engram neurons in the rat lateral amygdala. This study by Marios Abatis et al. demonstrates how fear conditioning strengthens synaptic connections between engram cells in the lateral amygdala, revealed through optogenetic identification of neuronal ensembles and electrophysiological measurements. The work provides crucial insights into memory formation mechanisms at the synaptic level, with implications for understanding anxiety disorders and developing targeted interventions. Presented by Dr. Kenneth Hayworth, this journal club will explore the paper's methodology linking engram cell reactivation with synaptic plasticity measurements, and discuss implications for memory decoding research.

SeminarNeuroscienceRecording

Memory Decoding Journal Club: Reconstructing a new hippocampal engram for systems reconsolidation and remote memory updating

Randal A. Koene

Co-Founder and Chief Science Officer, Carboncopies

Apr 8, 2025

Join us for the Memory Decoding Journal Club, a collaboration between the Carboncopies Foundation and BPF Aspirational Neuroscience. This month, we're diving into a groundbreaking paper: 'Reconstructing a new hippocampal engram for systems reconsolidation and remote memory updating' by Bo Lei, Bilin Kang, Yuejun Hao, Haoyu Yang, Zihan Zhong, Zihan Zhai, and Yi Zhong from Tsinghua University, Beijing Academy of Artificial Intelligence, IDG/McGovern Institute of Brain Research, and Peking Union Medical College. Dr. Randal Koene will guide us through an engaging discussion on these exciting findings and their implications for neuroscience and memory research.

SeminarNeuroscience

Consolidation of remote contextual memory in the neocortical memory engram

Jun-Hyeong Cho

Oct 26, 2023

Recent studies identified memory engram neurons, a neuronal population that is recruited by initial learning and is reactivated during memory recall. Memory engram neurons are connected to one another through memory engram synapses in a distributed network of brain areas. Our central hypothesis is that an associative memory is encoded and consolidated by selective strengthening of engram synapses. We are testing this hypothesis, using a combination of engram cell labeling, optogenetic/chemogenetic, electrophysiological, and virus tracing approaches in rodent models of contextual fear conditioning. In this talk, I will discuss our findings on how synaptic plasticity in memory engram synapses contributes to the acquisition and consolidation of contextual fear memory in a distributed network of the amygdala, hippocampus, and neocortex.

SeminarNeuroscience

Making memories in mice

Sheena Josselyn

The Hospital for Sick Children

Jul 1, 2021

Understanding how the brain uses information is a fundamental goal of neuroscience. Several human disorders (ranging from autism spectrum disorder to PTSD to Alzheimer’s disease) may stem from disrupted information processing. Therefore, this basic knowledge is not only critical for understanding normal brain function, but also vital for the development of new treatment strategies for these disorders. Memory may be defined as the retention over time of internal representations gained through experience, and the capacity to reconstruct these representations at later times. Long-lasting physical brain changes (‘engrams’) are thought to encode these internal representations. The concept of a physical memory trace likely originated in ancient Greece, although it wasn’t until 1904 that Richard Semon first coined the term ‘engram’. Despite its long history, finding a specific engram has been challenging, likely because an engram is encoded at multiple levels (epigenetic, synaptic, cell assembly). My lab is interested in understanding how specific neurons are recruited or allocated to an engram, and how neuronal membership in an engram may change over time or with new experience. Here I will describe both older and new unpublished data in our efforts to understand memories in mice.

SeminarNeuroscience

Imaging memory consolidation in wakefulness and sleep

Monika Schönauer

Albert-Ludwigs-Univery of Freiburg

Jun 17, 2021

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 during offline periods, such as quiet rest or sleep. My research investigates memory consolidation in the human brain with multivariate decoding of neural processing and non-invasive in-vivo imaging of microstructural plasticity. Using pattern classification on recordings of electrical brain activity, I show that we spontaneously reprocess memories during offline periods in both sleep and wakefulness, and that this reactivation benefits memory retention. In related work, we demonstrate that active rehearsal of learning material during wakefulness can facilitate rapid systems consolidation, leading to an immediate formation of lasting memory engrams in the neocortex. These representations satisfy general mnemonic criteria and cannot only be imaged with fMRI while memories are actively processed but can also be observed with diffusion-weighted imaging when the traces lie dormant. Importantly, sleep seems to hold a crucial role in stabilizing the changes in the contribution of memory systems initiated by rehearsal during wakefulness, indicating that online and offline reactivation might jointly contribute to forming long-term memories. Characterizing the covert processes that decide whether, and in which ways, our brains store new information is crucial to our understanding of memory formation. Directly imaging consolidation thus opens great opportunities for memory research.

SeminarNeuroscience

Coordinated hippocampal-thalamic-cortical communication crucial for engram dynamics underneath systems consolidation

Claudia Clopath

Imperial College London, UK

Apr 19, 2021

SeminarNeuroscienceRecording

Restless engrams: the origin of continually reconfiguring neural representations

Timothy O'Leary

University of Cambridge

Mar 5, 2021

During learning, populations of neurons alter their connectivity and activity patterns, enabling the brain to construct a model of the external world. Conventional wisdom holds that the durability of a such a model is reflected in the stability of neural responses and the stability of synaptic connections that form memory engrams. However, recent experimental findings have challenged this idea, revealing that neural population activity in circuits involved in sensory perception, motor planning and spatial memory continually change over time during familiar behavioural tasks. This continual change suggests significant redundancy in neural representations, with many circuit configurations providing equivalent function. I will describe recent work that explores the consequences of such redundancy for learning and for task representation. Despite large changes in neural activity, we find cortical responses in sensorimotor tasks admit a relatively stable readout at the population level. Furthermore, we find that redundancy in circuit connectivity can make a task easier to learn and compensate for deficiencies in biological learning rules. Finally, if neuronal connections are subject to an unavoidable level of turnover, the level of plasticity required to optimally maintain a memory is generally lower than the total change due to turnover itself, predicting continual reconfiguration of an engram.

engram

Latest

Memory Decoding Journal Club: Systems consolidation reorganizes hippocampal engram circuitry

Memory Decoding Journal Club: Neocortical synaptic engrams for remote contextual memories

Memory Decoding Journal Club: "Synaptic architecture of a memory engram in the mouse hippocampus

Motor learning selectively strengthens cortical and striatal synapses of motor engram neurons

Fear learning induces synaptic potentiation between engram neurons in the rat lateral amygdala

Memory Decoding Journal Club: Reconstructing a new hippocampal engram for systems reconsolidation and remote memory updating

Consolidation of remote contextual memory in the neocortical memory engram

Making memories in mice

Imaging memory consolidation in wakefulness and sleep

Coordinated hippocampal-thalamic-cortical communication crucial for engram dynamics underneath systems consolidation

Restless engrams: the origin of continually reconfiguring neural representations

Dynamic and selective engrams emerge with memory consolidation

One engram, two ways to recall it

Intrinsic neural excitability induces time-dependent overlap of memory engrams

Intrinsic neural excitability induces time-dependent overlap of memory engrams

Reduced correlations in spontaneous activity amongst CA1 engram cells

Distributed engrams enable parallel memory generalization and discrimination across brain regions

Acute circadian rhythm disturbance impairs contextual-memory engrams in the dentate gyrus

Acute stress via retrograde endocannabinoid signaling disrupts engram ensemble specificity to generalize threat memory in mice

Amygdalar regulation of memory engrams in the hippocampus: Spotlight on sex differences

Association between a previously remembered context and an aversive experience is accompanied by repeated activations of the same context engram neurons throughout the brain

CRISPR-based epigenetic editing of engram cells in fear memories

Distributed memory engrams underlie flexible and versatile neural representations

Engram competition modulates infant memory expression in development

Engram-specific synaptic potentiation is important for fear memory formation and expression in vivo

So excited to see you! Visual object-in-place learning increases neuronal excitability in lateral entorhinal cortex engram cells

Experience and reactivation status determine engram synapse structural connectivity

Hippocampal DNA methylation processes promote memory persistence by facilitating systems consolidation and cortical engram stabilisation

InhGrams for engrams: Inhibitory plasticity aids recall by disinhibition of excitatory-inhibitory engrams

Inhibitory synaptic remodeling of hippocampal engram neurons during episodic memory consolidation

Investigating the recruitment of parvalbumin and somatostatin interneurons into engrams for associative recognition memory

The microglial modulation of a memory engram in the context of Alzheimer’s disease

Molecular reprogramming of engram cells rescues memory in AD

Nogo-A regulates fear memory processes and memory engram formation by modulating neuronal excitability in a sex-specific manner

The parvalbumin-interneuron mediated modulation of a memory engram in the context of Alzheimer’s disease

Potential role for microRNA regulation in the tuning of engram recruitment during fear memory consolidation

The proteomic architecture of the synaptic engram supporting context memory

Revealing hidden targets in memory assemblies: The minimal engram for contextual memory encoding

Role of 4.1N in synaptic plasticity and engram modulation

Subpopulations of hippocampal inhibitory interneurons contribute differently to engram formation in APP/PS1 mice

Temporal dynamics of neuronal excitability in the lateral amygdala mediates allocation to an engram supporting conditioned fear memory

Temporal evolution of traumatic memory engrams in a mouse model of early-life stress

Termination of convulsion seizures by destabilizing and perturbing seizure memory engrams

What is long-term memory? Investigating the neuronal structures and molecular mechanisms of memory storage in engram cells

Whole brain mapping of engram distribution and stability