Sleep shapes the associative structure underlying pattern completion in multi-item event memory. Meaning Real-life events typically consist of multiple elements, such as a location, people, and objects, that become associated during the event. These associations may differ in their strength and some elements may be associated only indirectly (for example, through a third element). Here, we show that sleep , compared to night waking, selectively strengthens associations between event elements that were weakly encoded and those that were not encoded together, thus fostering new associations. Importantly, these sleep effects were associated with better recall of the entire event after presentation of a single cue. These findings uncover a critical role for sleep in completing partial information and are critical to understanding how real-life events are processed during sleep. |
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Researchers have known for some time that sleep consolidates our memories of episodic facts and events. However, research to date has focused primarily on simple associations, that is, connections between items, such as those we make when learning new vocabulary. "But in real life, events are usually made up of numerous components (for example, a place, people and objects) that are linked together in the brain," explains Dr. Nicolas Lutz from the LMU Institute of Medical Psychology. . These associations may vary in strength and some elements may be connected to each other only indirectly. "Thanks to the neural connections underlying these associations, a single keyword is often all it takes for someone to remember not just individual aspects of an event but multiple aspects at once." This process, known as pattern completion , is a fundamental feature of episodic memory. Lutz is the lead author of a study recently published in the journal Proceedings of the National Academy of Sciences (PNAS), which investigated the effect of sleep on memory for such complex events.
After study participants learned events with complex associations, in one condition they spent the night in a sleep laboratory, where they were allowed to sleep as usual, while in another condition, they had to stay awake all night. In both conditions, participants were allowed to spend the next night at home to recover. They were then tested on how well they could remember different associations between elements of the learned events. "We were able to show that sleep specifically consolidates weak associations and strengthens new associations between elements that were not directly connected to each other during learning. Furthermore, the ability to remember multiple elements of an event together, after being presented with only one cue, improved afterward. of sleep compared to the state in which the participants remained awake," summarizes Nicolas Lutz. This demonstrates the importance of sleep in completing partial information and processing complex events in the brain.
By monitoring the brain activity of the study participants during sleep, the study authors were also able to show that the improvement in memory performance is related to so-called sleep spindles : bursts of neuronal oscillatory activity during sleep, which are associated with the active consolidation of memory contents. This occurs by reactivating underlying neural structures while sleeping. "This finding suggests that sleep spindles play an important role in consolidating complex associations that underlie the completion of memories of entire events," said Professor Luciana Besedovsky, principal investigator of the study.
According to Lutz and Besedovsky, the identified effects of sleep on memory can be seen as an important adaptation of the human brain, because they help people draw a more coherent picture of their environment, which in turn allows them to make more complete predictions of the environment. future. "Our results reveal a new function through which sleep can offer an evolutionary advantage," considers Luciana Besedovsky. "In addition, they open new perspectives on how we store and access information about complex, multi-element events."
