Breathing, acting as a conductor, orchestrates hippocampal brain waves during sleep, a process essential for memory consolidation, according to a new Northwestern Medicine study. This groundbreaking study provides the first evidence of a direct link between breathing rhythms during sleep and key hippocampal brain waves—slow waves, spindles, and ripples—in humans. While the role of these brain waves in memory formation was well-established, this study unveils a crucial underlying mechanism that was previously unknown.
“To strengthen memories, three special neural oscillations emerge and synchronize in the hippocampus during sleep, but they were thought to come and go at random times,” said senior study author Christina Zelano, professor of neurology at Northwestern University Feinberg School of Medicine. “We discovered that they are coordinated by breathing rhythms.”
Northwestern scientists discovered that hippocampal oscillations occur at particular points in the breathing cycle, suggesting that breathing is a critical rhythm for proper memory consolidation during sleep.
“Memory consolidation relies on orchestration of brain waves during sleep, and we show that this process is closely timed by breathing,” said corresponding author Andrew Sheriff, a postdoctoral student in Zelano’s lab.
The study will be published Dec. 16 in the Proceedings of the National Academy of Sciences.
The findings have important implications for disordered breathing during sleep—such as sleep apnea—which is linked with poor memory consolidation.
The observation that sleep enhances memory has a long history, dating back to ancient Rome. The scholar Quintillian remarked on the “curious fact” that a single night’s rest significantly strengthens memory, foreshadowing the modern concept of memory consolidation. This process involves the intricate interplay of various brain waves within the hippocampus.
“When you’re sleeping, your brain is actively replaying experiences you had during the day,” Sheriff said.
Sheriff had just returned from a conference in Reykjavik, Iceland, where he had to learn his way around a new city. “The hippocampus plays a major role in forming a map of a new area,” Sheriff said. “I would wake up and feel I had a better representation of the city around me. That was facilitated by the oscillations that occurred during my sleep, which we found are coordinated by breathing.”
The study indicates people with disrupted breathing during sleep should seek treatment for it, Sheriff said.
“When you don’t get sleep your brain suffers, your cognition suffers, you get foggy,” Sheriff said. “We also know that sleep-disordered breathing is connected with stroke, dementia and neurodegenerative disorders like Alzheimer’s Disease.
“If you listen to someone breathing, you might be able to tell when they are asleep, because breathing is paced differently when you’re sleeping. One reason for that may be that breathing is performing a careful task: coordinating brain waves that are related to memory.”
