Memories are formed and stored during sleep, and a recent study has uncovered how this process continues throughout life without depleting neurons or brain cells.
Scientists discovered that specific areas of the hippocampus, a brain region related to memory formation and learning, become inactive during deep sleep, enabling the neurons to reset.
"This mechanism could allow the brain to reuse the same resources, the same neurons, for new learning the next day," said Azahara Oliva, an assistant professor of neurobiology and behaviour at Cornell University, US, and corresponding author of the study published in the journal Science.
While we are asleep, our brain cells review everything we learn or experience throughout the day by repeating the patterns that were activated initially. This process assists in how memories are stored.
This process, known as 'memory consolidation', is followed by the storing of memories in a large area in the brain known as the cortex. Both the hippocampus and the cortex are involved in memory formation, as the hippocampus transfers temporary or 'short-term' information to the cortex to create permanent or 'long-term' memories.
According to the researchers, the hippocampus is divided into three regions. Two of these regions are recognised for their role in forming memories related to time and space. As this study revealed, the third region is involved in silencing and resetting parts of the hippocampus during sleep.
"We realised there are other hippocampal states that happen during sleep where everything is silenced. The (two) regions that had been very active were suddenly quiet. It's a reset of memory, and this state is generated by the (third) region," Oliva said.
In the research, scientists inserted electrodes into the hippocampi of mice's brains, which are commonly studied due to their genetic similarity to humans. This enabled the researchers to monitor the brain's activity while the mice were learning and sleeping.
The findings of the study offer insight into why all animals need sleep - not only to consolidate memories but also to reset the brain and maintain its functionality during waking hours, according to the researchers.
The researchers believe that manipulating the processes involved in memory consolidation can now enhance memory.
They suggest that these techniques could be used in cases where memory function is impaired, such as in Alzheimer's disease, where memory and decision-making are affected, impacting daily life.
Furthermore, the researchers noted that the findings could potentially be used to explore methods for erasing negative or traumatic memories, which could be beneficial in treating conditions like post-traumatic stress disorder.
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