A team of neuroscientists from Northwestern University and clinicians from the University of Chicago Epilepsy Center has recently explored the role of sleep in consolidating memories. By recording electrophysiological responses to a series of sounds connected to daytime learning activities that were repeatedly presented to five participants during sleep, the experts found that the participants significantly improved their performance in a recall test the next morning, suggesting that sleep plays a crucial role in consolidating memory processing and storage.
The scientists enrolled a group of five epilepsy patients who had electrode probes implanted into the brain for the purpose of investigating potential treatments to their seizure disorders. During sleep, the participants were repeatedly exposed to 10-20 sounds, half of which were associated with objects and their precise spatial locations that patients learned before sleep.
The analysis revealed systematic improvements in spatial recall, with the object sounds presented during sleep eliciting increased oscillatory activity, including rises in theta, sigma, and gamma EEG bands, as well as significant activity in the hippocampus – a part of the brain that helps structuring and consolidating spatial and temporal patterns – and the adjacent temporal area of the cerebral cortex, reflecting the reactivation and strengthening of corresponding spatial memories.
“We are investigating how people manage to remember the things they’ve learned, rather than forgetting them,” said study senior author Ken Paller, the director of the Cognitive Neuroscience Program at Northwestern. “Our view is that sleep contributes to that ability.”
“The orthodox assumption used to be that such sounds would be blocked out when people are sleeping. Instead, these sounds allowed us to demonstrate that brain structures such as the hippocampus are responsive when memories are reactivated, helping us to retain the knowledge we gain when we’re awake.”
“At times, remembering and forgetting seems random. We can remember irrelevant details while forgetting what we most want to remember. The new answer to this long-standing mystery, highlighted by this research, is that memories are revisited when we sleep, even though we wake up not knowing it happened,” he concluded.
The study is published in the journal Proceedings of the National Academy of Sciences.
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