York Study Reveals Brain 'Tagging' Mechanism That Guides Memory During Sleep

Every day the brain takes in far more information than it can store, yet some experiences become lasting memories while others fade. Researchers at the University of York have identified a neural mechanism that determines, during learning itself, which experiences the brain will strengthen into long-term memories during sleep.

In a study published in the journal PLOS Biology, the team recorded brainwave activity in human participants as they learned new pairings between words and pictures. It has long been known that sleep helps convert freshly learned information into lasting memory, but how the brain selects which experiences to prioritize was not understood.

The researchers found that during learning, the brain 'tags' certain memories for processing later during sleep. This tagging was linked to a specific brainwave pattern called a theta rhythm, a rhythmic electrical signal in the brain that occurs during learning. The strength of the theta rhythm acted as an instructional cue: memories tied to a stronger theta rhythm during learning were preferentially strengthened during sleep, and this led to better recall afterward.

Lead author Dr. Dan Denis, from the Department of Psychology at the University of York, said the findings uncover, for the first time, a signature of neural activity that instructs the brain which experiences to process during sleep and turn into long-term memories. He said that if people remembered everything they experienced, the brain would quickly reach system overload, so selectively prioritizing emotionally significant or future-relevant events lets past experience guide behavior.

The researchers noted that while this selective filtering is normally useful, disruptions to it could play a role in psychiatric conditions. Denis said that in depression, people tend to overallocate attention to negative information while downplaying positive experiences. The study, titled 'Theta oscillations tag episodic memories for sleep-dependent consolidation,' was published in 2026.