Learn how Memory Engrams function as dynamic segments in the brain that evolve with memories influenced by new experiences.
How Brain Engrams Store and Transform Memories in Conceptual Space
Understanding Engrams and Conceptual Space
Scientists study how our brain stores memories through engrams, which are like the physical traces of memory in the brain. Imagine these engrams as segments laid out on a circle, representing a conceptual space. These segments can change location and size over time, depending on external stimuli, called Catching Shots (CS). When a CS hits an engram segment, it causes the engram to shift its position and become more focused or sharper, akin to how memory storage might adapt.
The concept space acts much like a circle where these segments exist. This simple one-dimensional model helps to understand how memories might behave—moving around and changing based on new experiences. The segments also tend to expand slowly when there are no new stimuli affecting them, showing how memories can fade or become less sharp over time, much like changes in memory storage over time.
How Stimuli Affect Engrams
When a stimulus strikes a segment, two important things happen:
- The center of the engram jumps to where the stimulus hits.
- The length shrinks or sharpens, increasing focus, much like memory storage becomes optimized.
This sharpening follows an exponential probability rule, meaning smaller lengths happen more often after being hit by a stimulus. Over time, when there’s no new stimulus, the engram slowly grows back in size but at a decreasing rate to model memory fading. This reflects a storage-like adaptation.
The Mystery of Memory Growth and Forgetting
The growth of these segments mimics memory forgetting processes. Interestingly, research suggests forgetting has both fast initial loss and slow long-term decay phases. In this model, that behavior is captured with a nonlinear equation—engrams don’t fade away instantly but instead gradually lose sharpness until they reach their largest (most faded) size, like a metaphor for memory storage capacity reaching its limits.
Kinetic Model Explains Memory Changes
This model uses an equation called the “engram kinetic equation” that explains how the distribution of segment sizes changes over time. It takes into account:
- The chance an engram is hit by stimuli and gets sharpened.
- The natural growth or fading occurs when there’s no stimulus.
- A balance between shrinking due to stimuli and growing because of forgetting, similar to fluctuations in memory storage systems.
This framework reveals that while engrams transform constantly, existing neural assemblies mainly adapt rather than vanish entirely. That means even faded memories persist in subtle forms until reinforced again by new experiences.
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Reference:
Otieno, W., Tyukin, I. Y., & Brilliantov, N. (2025). The critical dimension of memory engrams and an optimal number of senses. Scientific Reports, 15(1). https://doi.org/10.1038/s41598-025-11244-y
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