and the length of time spent in REM sleep are also reduced, while its latency increases. Poor sleep onset in AD has been associated with dream-related hallucination, increased restlessness, wandering and agitation that seem related to sundowning - a typical chronobiological phenomenon presented in the disease. The neurodegenerative conditions are commonly related to structural brain impairment, which might disrupt the states of sleep and wakefulness, circadian rhythm, motor or non motor functioning. On the other hand, sleep disturbances are frequently related to worsening patient's cognitive functioning, emotional state and quality of life. Furthermore, these abnormal behavioral symptoms negatively contribute to overwhelming their relatives and caregivers. The limited research related to it and the increasing life expectancy calls for a deeper understanding of the relationship between sleep disorders and neurodegenerative disease. Sleep disturbances and Alzheimer's Disease More than 70% of people with dementia are affected by Alzheimer's disease (AD). Despite this high number, our understanding of the underlying mechanisms for disease progression remains very limited. However, recent studies have highlighted a link between sleep disturbances and Alzheimer's disease. Sleep changes with normal aging. Over time, a decrease in time sleeping and a decrease in the quantity of NREM sleep can be observed, specifically in NREM SWS (less than 10% of the SWS is maintained). Older people also are more prone to insomnia or sleep apnea. In Alzheimer's disease, in addition to cognitive decline and memory impairment, there are also significant sleep disturbances with modified sleep architecture. The latter may consist in sleep fragmentation, reduced sleep duration, insomnia, increased daytime napping, decreased quantity of some sleep stages, and a growing resemblance between some sleep stages (N1 and N2). More than 65% of people with Alzheimer's disease have this type of sleep disturbance. One factor that could explain this change in sleep architecture is a change in circadian rhythm, which regulates sleep. A disruption of the circadian rhythm would generate sleep disturbances. Some studies show that people with AD have a delayed circadian rhythm, whereas in normal aging, an advanced circadian rhythm is present. In addition to these psychological symptoms, at a neurological level there are two main symptoms of Alzheimer's disease. The first is an accumulation of beta-amyloid waste forming aggregate "plaques". The second is an accumulation of tau protein. It has been shown that the sleep-wake cycle acts on the beta-amyloid burden, which is a central component found in AD. As