Neural network encoding memories

Decoding Memory: How Your Brain Finds the Right Neurons

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Mira Elwood in Mind & Education August 2025 • 4 min read.

"Unlocking the secrets of memory engrams and neuronal recruitment for a clearer understanding of brain function."


Our memories shape who we are, influencing our decisions, emotions, and understanding of the world. But how does the brain, with its billions of neurons, manage to store and recall these complex experiences? For decades, scientists have focused on the hippocampus, a brain region critical for forming episodic memories—memories of specific events, times, and places.

A groundbreaking area of study has emerged focusing on 'cellular engrams'. These are specific groups of hippocampal neurons believed to encode individual memories. Manipulating these neurons in animal models has demonstrated that activating a specific engram can trigger the recall of its associated memory. This begs a fascinating question: how does a memory 'find' its neurons among the vast network of the brain?

In a recent article in BioEssays, researchers França and Monserrat delve into this very puzzle, exploring how the brain recruits specific neurons into a memory engram. They challenge the traditional view that a neuron's activity is solely determined by its synaptic inputs and excitability, suggesting a more complex and dynamic process is at play.

The Neuron Selection Process: Beyond Simple Excitability

Neural network encoding memories

Traditionally, neurophysiology suggests that a neuron's activity is dictated by two primary factors: the sum of its synaptic inputs (excitatory and inhibitory signals from other neurons) and its intrinsic excitability (determined by its morphology and biophysical properties). This leads to a straightforward prediction: a specific memory should be uniquely linked to a specific engram. A particular set of sensory stimuli – a familiar scent, a vibrant color, or a distinct sound – should consistently activate the same group of neurons.

However, recent rodent experiments have thrown a wrench into this neat and tidy model. Researchers have found that manipulating the excitability of neurons doesn't always prevent memory formation. For example, inhibiting potential future engram cells during learning doesn't necessarily stop a new memory from forming. Instead, the memory appears to be stored in a different population of neurons, suggesting a degree of redundancy or flexibility in the system.

  • Synaptic Inputs: Neurons receive excitatory and inhibitory signals.
  • Intrinsic Excitability: Neuron's response to synaptic inputs.
  • Rodent Studies: Memories can form even if certain neurons are inhibited.
These findings challenge the idea that neurons are pre-selected for specific memories based solely on their existing connections and excitability. It raises the possibility that the brain employs a more stochastic, or random, recruitment process, where neurons are selected into engrams with their initial synaptic wiring playing a less dominant role than previously thought. This suggests a dynamic allocation process that allows the brain to adapt and create new memories even when certain neuronal pathways are disrupted.

Reframing the Memory Code: Multiple Dimensions and Future Directions

So, how can we reconcile the seemingly stochastic nature of engram formation with the fundamental principles of neurophysiology? França and Monserrat propose that individual neurons can represent multiple dimensions of information, encompassing both external stimuli and internal variables that are difficult to measure in typical experiments. While rodent studies often focus on the spatial aspects of memory, factors such as an animal's goals, attention, and even sensations like hunger or thirst can significantly influence neuronal activity.

About this Article -

This article was crafted using a human-AI hybrid and collaborative approach. AI assisted our team with initial drafting, research insights, identifying key questions, and image generation. Our human editors guided topic selection, defined the angle, structured the content, ensured factual accuracy and relevance, refined the tone, and conducted thorough editing to deliver helpful, high-quality information.See our About page for more information.

This article is based on research published under:

DOI-LINK: 10.1002/bies.201800189, Alternate LINK

Title: How Does A Memory Find Its Neurons?

Subject: General Biochemistry, Genetics and Molecular Biology

Journal: BioEssays

Publisher: Wiley

Authors: Christoph Schmidt-Hieber

Published: 2018-10-08

Everything You Need To Know

1

How does the brain store and recall memories?

The brain stores and recalls memories through a process involving specific groups of neurons called memory engrams. These engrams, primarily located in the hippocampus for episodic memories, are activated to retrieve associated memories. Manipulating these specific neurons in animal models triggers memory recall, highlighting their crucial role in how the brain functions.

2

What is the role of the hippocampus in memory?

The hippocampus is a critical brain region for forming episodic memories—memories of specific events, times, and places. The hippocampus's role in memory is essential for understanding how the brain encodes and retrieves memories. Recent research focuses on the role of cellular engrams within the hippocampus to uncover the complex processes behind memory.

3

How are neurons selected for memory?

Neuron selection is a complex process that goes beyond simple excitability and synaptic inputs. Traditionally, neurons' activity is determined by their synaptic inputs and intrinsic excitability. However, experiments show that inhibiting neurons doesn't always prevent memory formation. This suggests a more dynamic recruitment process, where the brain may select neurons into engrams in a stochastic or more random manner, and the initial synaptic wiring is less dominant.

4

What are cellular engrams, and why are they important?

The term "cellular engrams" refers to specific groups of hippocampal neurons that encode individual memories. Their significance lies in their role in storing and recalling memories. Recent research shows that activating a specific cellular engram can trigger the recall of its associated memory, showing how these engrams are a crucial aspect of memory retrieval.

5

What new perspective do França and Monserrat offer on memory coding?

França and Monserrat propose that individual neurons can represent multiple dimensions of information, encompassing both external stimuli and internal variables. Factors like an animal's goals, attention, and internal states can significantly influence neuronal activity. This reframing of the memory code suggests a more dynamic allocation process and the ability of the brain to create new memories even when certain neuronal pathways are disrupted.

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