Imagine you’re a student, it’s finals week, and you’re preparing for a big exam: do you pull an all-nighter or do you get some rest?
As many a groggy-eyed person who’s stared blankly at a test knows, a lack of sleep can make it extraordinarily difficult to retain information.
Two recent studies from University of Michigan shed light on the reasons behind this difficulty and the impact of sleep and sleep deprivation on the brain’s ability to form and retain memories.
The brain’s activity during sleep and sleep deprivation can either benefit or harm memory formation. Specific neurons can respond to specific stimuli, such as rats in a maze having neurons that light up when they reach certain spots. These place neurons also help people navigate their surroundings. But what occurs during sleep? Dr. Kamran Diba, an associate professor of Anesthesiology at U-M Medical School, questions what can be inferred if a neuron is active during sleep. A recent study conducted, published in the journal Nature and headed by Diba and former graduate student Kourosh Maboudi, Ph.D., examines neurons in the hippocampus, a seahorse-shaped structure deep in the brain that is involved in memory formation. The study found a method to visualize the tuning of neuronal patterns associated with a specific location while an animal is asleep.
During restful states and sleep, a type of electrical activity known as sharp-wave ripples is emitted from the hippocampus every few seconds over the course of many hours. Researchers have been fascinated by the synchronicity and distance traveled by these ripples, which seem to spread information.The transfer of information from one part of the brain to another occurs through the firing of neurons. These firings are believed to be essential for neurons to create and update memories, particularly those related to location. In a recent study, researchers measured the brain activity of rats while they were sleeping after completing a new maze. Using Bayesian learning, they were able to identify which neurons were responsive to different areas in the maze for the first time. This involved observing how certain neurons would activate together during sleep if they shared a similar preference for a particular corner of the maze.The team discovered that when a specific cell in the brain was activated during the sleep, its location preferences of neurons changed depending on which other cells they fired with. This method allowed them to observe the real-time plasticity or representational drift of the neurons. This finding supports the theory that reactivation of neurons during sleep is crucial for memory formation, highlighting the importance of sleep for memories. The team also wanted to investigate the effects of sleep deprivation on the brain in a separate study.Nature: Diba and former graduate student Bapun Giri, Ph.D., led the team in comparing the amount of neuron reactivation and the sequence of their reactivation during sleep and sleep loss. They found that the firing patterns of neurons involved in reactivating and replaying the maze experience were higher during sleep compared to sleep deprivation. Sleep deprivation was associated with a similar or higher rate of sharp-wave ripples, but lower amplitude waves and lower power ripples.
Diba stated that in almost 50% of cases, the reactivation of the maze experience during sharp-wave ripples was completely suppressed during sleep deprivation. When sleep-deprived rats were able to catch up on sleep, he added, the reactivation rebounded slightly, but it never matched that of rats who slept normally. Additionally, replay was similarly impaired but was not recovered when lost sleep was regained.
Given that reactivation and replay are important for memory, these findings demonstrate the detrimental effects of sleep deprivation on memory.
Diba’s team hopes to continue examining the nature of memory processing.
The article discusses the importance of brain waves during sleep and why it is necessary for them to be reactivated. It also examines the impact of sleep pressure on memory. The authors of the article are Hiroyuki Miyawaki, Caleb Kemere, Nathaniel Kinshy, Utku Kaya, and Ted Abel.