It’s no surprise that sleep and memory have a strong relationship. However, in a recent study, researchers from the University of Michigan discovered further information about the critical role sleep plays in learning and memory formation.
The findings, published in the journal Nature Communications, reveal the negative impact that sleep deprivation has on the region of the brain’s hippocampus called the “CA1.” The hippocampus is responsible for forming long-term memories.
Although it’s long been known that sleep has a direct connection to memory formation and other brain functions, what makes this new research stand out from previous studies is that it points to the exact location in the brain that sleep deprivation affects. By conducting a series of experiments on mice, the researchers made a number of discoveries about how a lack of sleep interferes with the rhythm of “neuronal firing,” also called oscillations, which inhibits long-term memory formation.
To better understand and assess the brain activities of a group of mice, researchers moved the mice from their home environments to a foreign setting, then issued them mild foot shocks as they explored the new area. When they returned the mice to their home cages to rest, the researchers observed that the mice that got an adequate amount of sleep after the experience had stronger oscillations in the CA1, compared to sleep-deprived mice.
That showed the researchers that adequate sleep is correlated with strong oscillations in the CA1. Their next step was to uncover the extent to which oscillations in this area of the brain relate to memory formation. They gave a new group of mice a small dose of a drug that prevents neurons in the CA1 from expressing the protein “parvalbumin,” a process that naturally occurs with sleep deprivation and weakens CA1 oscillations. Then, when they put the mice back in an environment where they had received foot shocks previously, the mice did not demonstrate that they had any memory of having been in that environment before. They didn’t act fearful of being shocked again.
These findings challenge scientists’ current understanding of memory formation. Memories, these researchers found, are not stored in single cells, but in a neural network. It also indicated a direct relationship between sleep and learning or memory formation.
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"It seems like this population of neurons that is generating rhythms in the brain during sleep is providing some informational content for reinforcing memories,” said senior study author Sara Aton, an assistant professor in the Department of Molecular, Cellular and Developmental Biology at the University of Michigan, in an interview with Medical News Today. “The rhythm itself seems to be the most critical part, and possibly why you need to have sleep in order to form these memories."