How Memories Crystalize in the Brain

This piece, by Onno Berkan, was published on 02/11/25. The original text, by Bellafard et al., was published by Nature on 05/15/24.

This UCLA study from the Golshani Lab investigated how the brain stores and processes temporary information, known as working memory, and how these memory processes change as animals learn and become experts at a task. The scientists trained mice to perform a memory task in which they had to remember odors for five seconds before making decisions based on what they smelled.

The researchers focused primarily on a brain region called the secondary motor cortex (M2), which they discovered plays a crucial role in maintaining working memory. They used advanced imaging techniques to observe the activity of thousands of neurons while mice performed the task. They used one- and two-photon imaging to track neural activity over a week.

One of the study's key findings was that the way the brain stored working memory information changed dramatically as the mice became experts. During the early expert phase, the memory representations were unstable and would change daily. However, with continued practice, these memory patterns eventually stabilized and became more consistent.

The researchers found that interfering with neuron activity in the M2 region during specific periods severely impacted the mice's performance, confirming this brain area's importance for working memory. However, this interference didn't fully prevent the mice from learning the task, suggesting that other brain regions might also be involved in the learning process.

The study revealed an important principle about working memory: during the learning phase and early expertise, the brain's memory representations are malleable. This flexibility might be beneficial, allowing the brain to adapt quickly to new information and rules. However, with continued practice, these memory patterns eventually "crystallize" and become permanent.

The researchers also observed that while some aspects of memory (like initial odor recognition and final choice) stabilized relatively quickly, the working memory component took longer to become permanent. This suggests that different aspects of memory processing follow different timelines for development and stabilization.

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