The Critical Role of Sleep in the formation of memories

As finals week approaches, students often face the dilemma of pulling an all-nighter or getting some rest. Lack of sleep can severely impair information retention, as revealed by two new studies from the University of Michigan. These studies explore the brain’s activities during sleep and sleep deprivation and their impact on memory formation.

Neurons can be tuned to specific stimuli. For instance, in a maze, rats have neurons, called place neurons, that activate at specific locations. These neurons help in navigating the environment and are also active in humans. The question is, what happens to these neurons during sleep?

Kamran Diba, Ph.D., associate professor of Anesthesiology at U-M Medical School, and his team, including former graduate student Kourosh Maboudi, Ph.D., investigated neurons in the hippocampus, a brain structure involved in memory formation. Their study, summarized in the journal “Nature”, discovered a way to visualize neuronal patterns associated with locations during sleep.

The hippocampus generates electrical activity called sharp-wave ripples during restful states and sleep, occurring every few seconds over many hours. These ripples are believed to help neurons form and update memories. The researchers measured a rat’s brain activity during sleep after it completed a new maze and used Bayesian learning to track which neurons responded to specific places in the maze.

They found that neurons that preferred certain maze locations co-activated with other neurons during sleep. This neuronal plasticity or representational drift shows that sleep is crucial for memory formation. The study supports the theory that neuron reactivation during sleep is vital for memory consolidation.

Given the importance of sleep, the researchers examined the effects of sleep deprivation on the brain. In the second study, also published in “Nature”, Diba’s team, including former graduate student Bapun Giri, Ph.D., compared neuron reactivation and replay during sleep versus sleep deprivation. They found that neurons involved in reactivating and replaying maze experiences fired more frequently during sleep than during sleep deprivation. Although sleep-deprived rats experienced a similar or higher rate of sharp-wave ripples, the waves had lower amplitude and power.

In almost half of the cases, maze experience reactivation during sharp-wave ripples was entirely suppressed during sleep deprivation. When sleep-deprived rats caught up on sleep, their reactivation slightly rebounded but never matched that of rats who slept normally. Additionally, replay was impaired and did not recover with regained sleep.

These findings demonstrate the detrimental effects of sleep deprivation on memory, as reactivation and replay are crucial for memory processing. Diba’s team aims to continue studying memory processing during sleep, the necessity of reactivation, and the impact of sleep pressure on memory.

Story Source: Materials provided by Michigan Medicine – University of Michigan. Original written by Kelly Malcom [Link] | Content may be edited for style and length.