The Mystery of Memory Formation: How Our Brain Stores Information

Summary: Memory formation occurs through the continuous creation of new patterns of connectivity between specific engram cells in different regions of the brain.

Engram cells are activated by experiences and changes to retain information in our brain. The research used genetic and optogenetic techniques to study how engram cells form connections and identified a protein involved in regulating this connectivity.

This study sheds light on the mechanism behind memory storage in the brain and provides insight into how we learn and remember.

Highlights:

1. Memory engram cells are groups of brain cells that change and retain information based on specific experiences, allowing us to remember those experiences later.
2. The study used genetic and optogenetic techniques to monitor the formation of new connections between engram cells, revealing a molecular mechanism mediated by a synaptic protein.
3. Understanding the cellular mechanisms of memory formation advances our knowledge of how the brain processes information and forms memories.

Source: TCD

What is the mechanism that allows our brains to incorporate new information about the world and form memories?

New work by a team of neuroscientists led by Dr Tomás Ryan from Trinity College Dublin shows that learning occurs through the continuous formation of new patterns of connectivity between specific engram cells in different regions of the brain.

Whether on purpose, accidentally or simply by accident, we are constantly learning and therefore our brains are constantly evolving. When we navigate the world, interact with each other, or consume media content, our brains take in information and create new memories.

The next time we walk down the street, meet our friends, or come across something that reminds us of the last podcast we listened to, we will quickly re-engage that memory information somewhere in our brain. But how do these experiences modify our neurons to allow us to form these new memories?

Our brains are organs composed of dynamic networks of cells, always in motion due to growth, aging, degeneration, regeneration, daily noise and learning. The challenge for scientists is to identify “the difference that makes the difference” in the formation of a memory – the change in a brain that stores a memory is called an “engram,” which preserves the information for later use.

This recently published study aimed to understand how information can be stored as engrams in the brain.

Dr. Clara Ortega-de San Luis, postdoctoral researcher at Ryan Lab and lead author of the paper published today in the leading international journal, Current biologysaid:

“Memory engram cells are groups of brain cells that, activated by specific experiences, change to incorporate and thus retain information in our brain. Reactivation of these memory “building blocks” triggers the recall of specific experiences associated with them. The question is: how do engrams store meaningful information about the world?

To identify and study the changes that engrams undergo and which allow us to encode a memory, the team of researchers studied a form of learning in which two similar experiences become linked by the nature of their content.

The researchers used a paradigm in which animals learned to identify different contexts and form associations between them. Using genetic techniques, the team crucially labeled two different populations of engram cells in the brain for two discrete memories, then monitored how learning manifested through the formation of new connections between these engram cells.

Then, using optogenetics, which allows the activity of brain cells to be controlled with light, they then demonstrated how these newly formed connections were necessary for learning. In doing so, they identified a molecular mechanism mediated by a specific protein located in the synapse and involved in the regulation of connectivity between engram cells.

This study provides direct evidence that changes in synaptic wiring connectivity between engram cells are considered a likely mechanism of memory storage in the brain.

Commenting on the study, Dr Ryan, Associate Professor in Trinity’s School of Biochemistry and Immunology, Trinity Biomedical Sciences Institute and Trinity College Institute of Neuroscience, said:

“Understanding the cellular mechanisms that enable learning helps us to understand not only how we form new memories or modify pre-existing ones, but also to advance our knowledge to unravel how the brain works and the mechanisms necessary for it to process thoughts and information.

“In 21^st In neuroscience of the last century, many of us like to think of memories as being stored in engram cells, or their subcomponents. This study argues that rather than looking for information inside or at the cell level, we should look for information between cells, and that learning can work by changing the brain’s wiring diagram – less like a computer and more like a developing sculpture.

“In other words, the engram is not in the cell; the cell is in the engram.

About this memory search news

Author: Thomas Deane
Source: TCD
Contact: Thomas Deane – TCD
Picture: Image is credited to Neuroscience News

Original research: Closed access.
“Engram cell connectivity as a mechanism of information encoding and memory function” by Tomás Ryan et al. Current biology

Abstract

Engram cell connectivity as an information coding mechanism and memory function

Strong points

• Connecting two distinct memories induces new connectivity between the underlying engrams
• Changes in engram cell-specific synaptic wiring are required to update a memory
• Engram cells undergoing connectivity plasticity exhibit structural changes
• Inactivation of engram-specific PSD-95 affects connectivity and impairs extinction

Summary

Information derived from experiences is incorporated into the brain as changes in sets of cells, called engram cells, that allow memory storage and recall. The mechanism by which these changes contain specific information is unclear.

Here we test the hypothesis that specific synaptic wiring between engram cells is the substrate for information storage.

First, we monitor how learning changes the pattern of connectivity between engram cells at the level of a monosynaptic connection involving the hippocampal ventral CA1 (vCA1) region and the amygdala.

Next, we evaluate the functional significance of these connectivity changes by artificially activating or inhibiting its presynaptic and postsynaptic components, respectively.

Finally, we identify a synaptic plasticity mechanism mediated by postsynaptic density protein 95 (PSD-95), which impacts the pattern of connectivity between engram cells and contributes to the long-term stability of memory.

These findings impact our theory of learning and memory by helping us explain the translation of specific information in engram cells and how these connections shape brain function.