Scientists have identified a neural process that helps the brain determine which memories are stored long-term and which are allowed to fade. Researchers from the University of York, Ludwig Maximilian University of Munich, and Baylor University in Texas have found that the brain applies a special “tag” to important experiences as they occur, marking them for consolidation during sleep.

The study focused on patterns of electrical activity in the brain known as “theta rhythms,” which are produced by thousands of neurons firing in synchrony and oscillating between three and eight cycles per second. These rhythms are believed to facilitate episodic learning by binding various aspects of an experience—such as sights, sounds, smells, and emotional responses—into a coherent memory.

In experiments, participants were shown pairs of words and unrelated images, for example, the word “coffee” paired with a picture of a football. Researchers measured the strength of theta rhythm activity while participants encoded these pairs. They discovered that stronger theta rhythms served as a sort of neural “tag,” signaling to the brain which memories should be preserved during subsequent sleep. After a two-hour nap, participants were more likely to recall the word-image pairs that had elicited stronger theta activity.

Further analysis revealed that these tagged memories were associated with increased coupling between two types of brainwaves during sleep, enhancing the integration of those experiences into long-term storage. This coupling suggests that the waking brain sets a priority for memory processing to occur during sleep.

Dan Denis, a psychologist at the University of York, stated that while it has long been known that sleep plays a crucial role in memory consolidation, it remained unclear how the brain prioritizes which memories to retain. This study provides new insight by identifying a neural signature that appears to guide the selection of memories for long-term retention.

Although the exact criteria for which events receive a strong tagging remain uncertain, researchers suggest that emotional significance or the future relevance of an experience may influence the process. The findings align with concepts illustrated in popular culture, such as the Pixar film Inside Out, where characters inside a young girl’s mind decide which memories to keep and which to discard.

Overall, the research advances understanding of the complex mechanisms behind memory formation, highlighting the interplay between waking brain activity and sleep in shaping lasting memories.