New research shows real-time neuroplasticity during sleep, with neurons replaying past events and anticipating the future. Caleb Kemere, an associate professor at Rice University, contributed to this study, which was published in Nature. The study reveals how neurons in rats hippocampus adjust and stabilize spatial memories after they run a maze for the first time.
Certain neurons respond to specific stimuli. Neurons in the visual cortex react to visual stimuli, while the neurons we study have place preferences.
Diba and Rice neuroscientist Caleb Kemere are researching how these neurons create a representation of the world after new experiences. They track sharp wave ripples, a neuronal pattern that helps consolidate new memories. They observed how these neurons stabilize spatial memories during rest.
Sleep is essential for memory and learning, as proven by better memory test performance after a nap than after staying awake or experiencing sleep deprivation.
Decades ago, researchers found that neurons in sleeping animals replay their exploration of new settings. This supports the idea that sleep helps turn new experiences into stable memories, suggesting that hippocampal neurons maintain stable spatial representations during sleep. However, researchers wanted to explore further.
The study, led by Kourosh Maboudi, a postdoctoral researcher at the University of Michigan, aimed to delve deeper into neuroplasticity during sleep. Caleb Kemere, a key contributor to the study, explains that they hypothesized that some neurons might alter their representations, akin to how we sometimes wake up with new insights. To test this, they meticulously tracked how individual neurons learn new routes or environments, providing invaluable insights into the brain’s adaptability during sleep.
Researchers trained rats to run on a track and observed how neurons in their hippocampus would “spike.” By calculating the average spiking rate, they estimated each neuron’s place field or the area it was most active in.
Their innovation was a machine learning approach that mapped where the animal was dreaming of being and used this to estimate each neuron’s spatial tuning during sleep.
Kamran Diba called the ability to track neuron preferences without a stimulus a breakthrough. He and Caleb Kemere praised Kourosh Maboudi, the study’s lead author, for developing this tuning method.
The method showed that most neurons maintain stable spatial representations during post-experience sleep. However, some neurons did more than stabilize memories.
Kemere found that some neurons change during sleep, which can be confirmed when animals revisit the environment. It’s like the second exposure happens while they’re asleep. This is significant because it shows neuroplasticity during sleep, unlike most research on waking periods.
According to Kamran Diba, Brain rewiring needs fast timescales. He notes that experiences can last from seconds to days, but memories are instant. He references Marcel Proust’s idea that a brief memory can unlock a world of past experiences.
The study highlights advances in neuroscience thanks to new neural probes and machine learning. Caleb Kemere expressed optimism for the progress of future brain science. However, he was also concerned about the impact of recent budget cuts on research.
Rice neuroscientist Caleb Kemere said, “It’s quite possible that if we were starting this work today, we might not have been able to do these experiments and get these results. “We’re grateful that the opportunity was there.”
Also Read: Scientists monitored brains replaying memories in real-time
Journal reference:
- Maboudi, K., Giri, B., Miyawaki, H. et al. Retuning of hippocampal representations during sleep. Nature. DOI: 10.1038/s41586-024-07397-x.