The link between NREM sleep oscillations and brain plasticity

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Sleep plays a crucial role in learning and memory. Increasing evidence supports the idea that brain areas that have been used more than others need more sleep. Specific types of brain waves (measured with an electroencephalogram) during non-rapid-eye-movement (NREM) sleep, such as slow waves (0.3-4 Hz) and spindles (12-15 Hz), are particularly involved in brain plasticity, i.e. the ability to reorganize neural pathways based on experience. Interestingly, our research showed that aging strongly modulates slow waves and spindle during sleep. Yet the mechanisms underlying age-related changes in slow waves and spindles and their functional consequences are still unknown. Our main hypothesis is that age-related changes in slow waves and spindles are associated with changes in the brain's ability to reorganize neural pathways. To test this, we will evaluate how sleep impacts brain plasticity and how changes in brain plasticity modify sleep in young and older subjects. Specifically, we will assess whether a 12-hour interval with or without sleep better maintains cerebral plasticity induced by transcranial magnetic stimulation (an innovative technique to manipulate brain activity) or performance on a memory task and consequent cerebral activation, as measured with brain imaging. We will also evaluate in young and older subjects how a change in brain activity induced by transcranial magnetic stimulation or a memory task impacts slow waves and spindles during subsequent sleep. We hope to provide essential cues as to how age-related changes in NREM sleep oscillations and in brain plasticity are interrelated.