New research from Western University neuroscientists, in collaboration with clinicians in the Epilepsy Monitoring Unit at London Health Sciences Centre (LHSC), has found a potential connection in the brain for building long-term memories.

The study, supported by Western’s BrainsCAN and published in eLife, measured neural recordings during sleep and found that sleep spindles – a specific rhythm of neural activity that occurs during sleep – take place across multiple areas of the cortex more frequently than originally thought. Spindles are known to be essential for the consolidation of long-term memory. Detecting these widespread sleep spindles provides a better understanding of how the brain forms memories. 

“We found these really interesting intricate dynamics where sometimes, sleep spindles are very local and constrained to one area of cortex, and at other times, they are global patterns where neurons from different regions all across the cortex are talking to each other,” said Lyle Muller, senior author of the paper and assistant professor in the department of mathematics at Western.

Adapting machine learning algorithms originally developed for detecting earthquakes and gravitational waves, the researchers completed a thorough analysis of neural recordings during sleep – providing a neural circuit mechanism for how activity patterns are connected across the brain. 

“Memories are first formed in the hippocampus. What sleep spindles do is help with the transfer of a memory from the hippocampus to long-term storage in the brain’s cortex,” said Maryam Mofrad, first author of the paper and Western postdoctoral scholar. “Identifying spindles is not easy; however, we developed a novel approach for sleep spindle recordings that is robust to the noise we’d typically see, allowing us to detect spindles occurring across multiple areas of the cortex during sleep.” 

In addition to finding that sleep spindles are happening across the brain more frequently, the team of researchers also discovered that learning a complex memory task during the day triggers more widespread spindles at night. 

As Muller explained, learning to recognize new pictures – like studying diagrams for a test – is an example of an activity that led to increased multi-area sleep spindles. The widespread sleep spindles help consolidate memories in the brain’s cortex, allowing the information to be stored as a long-term memory. “After sleep, you’ll remember the information better the next day than if you pulled an all-nighter.”

Discovering that sleep spindles are not isolated to one area is essential to understanding how different parts of the brain work together to develop long-term memories. To link up activity patterns and build stronger connections, neural circuits in the brain must connect with one another. 

“It’s not just single regions, like one motor area or one visual area, that are responsible for storing memories. It’s something more sophisticated, like combinations of visual and motor areas that might be storing visual and motor components of a memory,” said Muller. “We're at the outset of that, but this work has made that view of spindles possible.”

The new insight into sleep spindles and how the brain stores memories is giving researchers a better understanding of how long-term memories are formed, and how these results might be used to help those with memory issues. 

“These results could lead to future studies on the underlying mechanisms that might cause memories to falter after normal aging or in memory disorders like Alzheimer’s disease,” said Mofrad.  

“The findings point to the idea that memory consolidation involves a sophisticated and dynamic process. The brain may have lots of various specific mechanisms to produce robust memory consolidation that we just don't know yet,” said Muller. “Once we understand that, we may be able to leverage it into improving memory consolidation.”