Scientists from Rice University and the University of Michigan have discovered that certain neurons in the brain not only replay past experiences during sleep but may also anticipate future events
Published in the journal Nature, this study provides insights into how individual neurons in the hippocampus, a critical area for memory and learning, stabilise and adjust spatial representations during rest.
The brain predicts future events
Led by Kamran Diba, an associate professor of anesthesiology at Michigan, and Caleb Kemere, a neuroscientist at Rice, the research tracked the activity of neurons in rats as they navigated a maze.
By examining sharp wave ripples, and patterns of neuronal activation known to consolidate memories, the team observed how these neurons replayed and potentially predicted the animals’ future movements.
“For the first time in this paper, we observed how these individual neurons stabilise spatial representations during rest periods,” said Kemere.
Decades ago, scientists found that neurons in sleeping animals replayed their movements from recent explorations, supporting the idea that sleep helps solidify new memories. However, Kemere and his team aimed to explore whether these neurons might also adapt and learn during sleep, reflecting our own experiences of waking up with new insights into problems.
Learning during sleep
The researchers trained rats to run back and forth on a track, rewarding them with liquid at either end. They then monitored how specific neurons, known as place cells, fired in response to different locations on the track. The challenge was to assess these place cells’ activity during sleep when the rats were not moving.
“We addressed this challenge by relating the activity of each individual neuron to the activity of all the other neurons,” explained Diba. This innovative approach allowed the researchers to map out where the animals might be “dreaming” of being, providing insights into the spatial tuning process of each neuron.
The study revealed that most neurons maintain stable spatial representations during sleep, but some undergo changes that prepare the brain for future experiences. When the rats revisited the maze, these changes were validated, suggesting that some learning occurs during sleep.
“The thing that I loved the most about this research and the reason that I was so excited about it is finding that it’s not necessarily the case that during sleep the only thing these neurons do is to stabilise a memory of the experience,” Kemere said.
This research marks a significant advancement in understanding neuroplasticity, and how neurons rewire and form new connections, during sleep. Traditionally, studies focused on waking periods when stimuli are present. The new findings show the brain’s ability to undergo rapid rewiring in response to experiences compressed into memories.
This study, supported by technological advancements in neural probes and machine learning, could reshape our understanding of memory and learning.
