Cross-frequency coupling of brain oscillations during human non-rapid-eye-movement (NREM) sleep: implications for cognitive function and memory consolidation.

点击翻译按钮获取中文摘要

The sleeping brain is characterized by rhythmic oscillations of electrical activity produced by neurons, and detectable using electrodes placed on the scalp during an electroencephalogram (EEG). Increasing evidence suggests that these oscillations are important for memory consolidation processes taking place during sleep. The three major brain rhythms that have been investigated in that regard are : 1) slow oscillations, high-amplitude low-frequency rhythms that are predominant during the deepest stages of sleep (stage N3); 2) sleep spindles, waxing-and-waning faster oscillations that are mainly found during intermediate stages of sleep (stage N2); 3) gamma oscillations, the fastest rhythms among these three oscillations, and known to be important for the learning of new information. Past research studies have shown that these oscillations increase during sleep after learning, suggesting their involvement in the offline consolidation of memory traces. More recent evidence however suggests that beyond their individual occurrence it is their degree of interactions that relates to memory consolidation. In other words, the degree to which brain oscillations during sleep tend to occur together (e.g., slow oscillation with spindles, and spindles with gamma oscillations), a process called cross-frequency-coupling (CFC), seems to play a major role in how sleep benefits memory. The objective of the proposed research program is to investigate the interactions between slow oscillations, spindles and gamma rhythms during sleep and their relationship with the recall of information learnt prior to sleep. To achieve this objective, we will use EEG and brain imaging techniques (in particular functional magnetic resonance imaging, or fMRI) to study brain oscillations during sleep and relate them to memory performance during the daytime. We will perform these studies in groups of young and old healthy volunteers, in order to assess how aging affects CFC of brain oscillations during sleep and their relation to memory performances. We hypothesize that a higher CFC during sleep will be associated with a better recall of information after sleep, and that aging will be characterized by lower CFC during sleep in association with poorer memory performances. The current project will shed new light on the mechanisms and functions of sleep, particularly how sleep benefits memory consolidation processes, and how these mechanisms might be impaired with aging.