Alzheimer's disease (AD) is characterised by a progressive loss of memory and cognitive function. In the early stages of AD, there is a progressive accumulation of molecules: β-amyloid peptides (Aβ) in the brain. There is a link between the accumulation of Aβ peptides and the deterioration of sleep, but current knowledge does not confirmed this link. The objective of this study is to define whether there is a link between cognitive decline and sleep disorders. If a correlation is found, this could allow earlier treatment of sleep disorders in the longer term in order to slow the development of AD.