“A central question in neuroscience.”
Sleep is critical to our mental and physical wellbeing — it constitutes about a third of our lives, and research provides strong evidence that sleep is central for learning and forming long-term memories.
“But exactly how such memory is formed is not well understood and remains, despite considerable research, a central question of inquiry in neuroscience,” according to a new press release on the topic.
Neuroscientists at the University of California, Riverside may finally have an answer to this question. In a first, their study provides a mechanistic explanation for how deep sleep (also known as slow-wave sleep) may bolster the consolidation of recent memories.
Consolidating a memory means to strengthen the memory in the brain, and while we’re fast asleep, our brains are still feverishly active and working to sort through our new memories and form long-term ones of the information that is important to keep.
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Despite the fact that human brains don’t respond to sensory input during sleep, the electrical activity is still up and running. In the hippocampus, a brain region associated with long-term memory, the researchers observed sharp-wave ripples, and in the cortex, they saw large, slow waves (oscillations).
These alternating patterns suggest that traces of memory acquired during wakefulness are initially stored in the hippocampus, and then progressively transferred to the cortex as long-term memory during sleep.
The neuroscientists used a computational model to come to these findings, and the results offer a link between the electrical activity during deep sleep and the synaptic connections between neurons. In fact, the patterns of slow waves in the cortex determine synaptic changes in the brain region, and change in synaptic strength is “widely believed to underlie learning memory storage in the brain,” according to the release.
"We interpret these results as a mechanistic explanation for the consolidation of specific memories during deep sleep,” said Yina Wei, a postdoctoral researcher and first author of the paper, “whereby the memory traces are formed in the cortex and become independent of the hippocampus."
“By influencing the nature of these oscillations, this hippocampal input activates selective memories during deep sleep and causes a replay of specific memories,” Wei continued. “During such memory replay, the corresponding synapses are strengthened for long-term storage in the cortex.”
Wei says that the results from their computational model, which can be found in the Journal of Neuroscience, can now be tested experimentally, including specific interventions to suppress or enhance the memory consolidation process.
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