For over a hundred years, scientists have been trying to demystify the connection between sleep and memory.
Many advances have been made – we have proven that sleep deprivation impairs learning; being tired makes it harder to focus, and that sleep is needed to fortify memories for recalling them later.
However, while researchers have always hypothesized that sleep improves our memory, we never had a good explanation for how. We may finally be getting closer to the truth.
Sleep may promote learning and memory
In June an exciting study was published by a joint US-China research team led by Wen-Biao Gan. The project, a collaboration between researchers at New York University and Peking University Shenzhen Graduate School experimented on mice using a special two-photon microscopy technique to examine what happens to neurons during sleep whilst learning.
Neurons, the basic building block of our nervous systems, transmit information throughout our brains and bodies. Gan focused on structures known as dendritic spines, tiny branch like structures that grow off of neurons.
These spines receive signals from the previous neuron, acting as a storage site for the neuronal connection and helping transmit electrical signals to the next neuron.
Of mice and memory
In the experiment, 15 live mice had microscopic “windows” carved into their skulls so that scientists could monitor the real-time growth of dendritic spines in the brain.
They focused on the motor cortex, the part of the brain that controls movement. Each mouse was then trained to balance atop a rotating rod.
Mice either learned to run forwards or backwards. After training, some of the mice were allowed to sleep for 7 hours, while others were kept awake.
Sleep after learning may strengthen memory
On examination, Gan’s team found a marked difference between the rested mice and the sleep-deprived mice. Sleep-deprived mice grew far fewer dendritic spines than rested mice.
As for the rested mice, their learning progress correlated to the rate of new spine growth. Rested mice also continued to develop new spines during the 24 hours after sleep and were more likely to retain their new spines.
First direct evidence that sleeping after learning may strengthen memory
Interestingly, spine growth was most dramatic during slow-wave, non-REM sleep. During slow-wave sleep, the neuronal branches that were previously used in learning were REACTIVATED.
Essentially, well-rested mice were learning more as their sleeping brains replayed activity from earlier. Tired mice, on the other hand, were missing out on the reactivation their brains needed to form new connections.
Discussing these results, Gan said
“We thought sleep helped, but it could have been other causes, and we show it really helps to make connections and that in sleep the brain is not quiet, it is replaying what happened during the day and it seems quite important for making the connections.” Source
Sleep and memory research moving forward
Fellow neuroscientists were enthusiastic about Gan’s results. They believe this study provides further evidence that our brains have “hot spots” for learning-driven neural growth. The research also reinforces previous findings that sleep loss can cause damage to our neurons.
Invigorated by these promising findings, Gan hopes to delve even deeper into the mysterious workings of sleep on our brains.
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