How the brain decides what to remember
A recent study(opens in new window) supported by the EU-funded MemOpt and SLEEPAWAY projects has shown that the brain likely ‘tags’ certain experiences when learning to better consolidate their memory during later sleep. Published in the journal ‘PLOS Biology’, the study offers new insights into the neural mechanisms through which our brains determine what information is retained for the future. Memories are not an unedited replay of daily events but rather a curated reel of our most salient experiences. This adaptive filtering is thought to be driven by a tagging process at the moment of learning, whereby certain memories are marked as important and prioritised for consolidation during offline periods, such as sleep. Without this selective mechanism, the brain would risk system overload, unable to distinguish critical information from the noise of everyday experience. While animal studies have provided compelling evidence that novelty, repetition and reward influence which memories are tagged for sleep-dependent processing, direct evidence for a similar mechanism in humans has remained elusive. The new study addresses this gap, offering the first clear neural evidence that the human brain does indeed prepare specific memories for overnight strengthening at the very moment they are formed. “How the brain decides what is important to remember and what can be forgotten is still a mystery,” the study authors comment in a ‘EurekAlert!’ news release(opens in new window). “These new findings help to answer that question, by uncovering for the first time a signature of neural activity which instructs the brain which experiences to process during sleep and form into long-term memories.”
Decoding the brain’s memory signals
To probe this memory-selecting mechanism, the researchers recruited 31 healthy young adults and used electroencephalography (EEG) to measure patterns of brain activity as they learned sets of object-word pairs. Each participant was tested on the pairs immediately and again after a two-hour break, completing this procedure across two separate visits. During one visit they were allowed to nap, while during the other they watched nature documentaries. This allowed the research team to compare how material was retained following sleep versus wakefulness. The scientists analysed the participants’ EEG readings, decoding distinct brain states present at learning that corresponded to memories later consolidated during sleep, effectively matching the repetitive oscillations recorded during encoding to the items remembered after the rest period. They found that word-object pairs accompanied by theta oscillations in the 3-8 Hz range during learning were more likely to survive a period of sleep but not a period of wakefulness. This theta activity in turn predicted stronger coupling between slow oscillations and sleep spindles – bursts of neural activity in the sleeping brain – which were themselves associated with better memory performance after sleep. Although the study tested recall only after two hours, the findings point to theta oscillations as the neural cue by which the brain flags experiences for overnight consolidation. “Our new findings shed new light on the brain processes that dictate what is ultimately remembered, and may open new avenues for understanding and treating common mental health problems such as depression,” the authors state. The MemOpt (Optimising memory: Understanding the role of sleep in selective memory strengthening) project ended in 2024. SLEEPAWAY (Forgetting unwanted memories in sleep) ends in 2030. For more information, please see: MemOpt project SLEEPAWAY project
