By Dr Géraldine Rauchs

(posted 5th June 2018)

Sleep is an essential part of our lives. Its functions are multiple, including brain development during the first years of life, growth hormone secretion, memory consolidation and for the efficient functioning of our immune systems. Recent studies have suggested that sleep may also contribute to the elimination of waste products that accumulate in the brain during the day, notably the amyloid-beta peptide that is commonly associated with Alzheimer’s disease. If this is the case, poor sleep quality may increase the risk of this debilitating disease.

At the Inserm laboratory in Caen, we have spent almost five years exploring sleep quality in older adults. To do so, we have used a range of complementary tools: sleep questionnaires, actigraphy (the recording of a person’s movements over several days to provide information about activity-rest cycles) and polysomnography (the use of electrodes placed over the head to monitor sleep). The sleep measures obtained are combined with advanced neuroimaging techniques, including Magnetic Resonance Imaging (MRI) to measure the volume of the brain, and Positron Emission Tomography (PET) to measure its functioning or to visualize amyloid deposits, one of the typical lesions of Alzheimer’s disease.

Firstly, we have found that seniors who complain of recurring difficulties falling asleep present greater amyloid deposits than individuals who easily fall into the arms of Morpheus. In addition, people who frequently awaken during the night also have lower grey matter volume in a small brain area named the insula, involved in the generation of some sleep rhythms. These results were obtained from sleep questionnaires, but preliminary analyses using more objective sleep indicators confirm that poor sleep quality is associated with greater brain alterations and lower cognitive performance. At first sight, these results may appear particularly alarming. But it is important to keep in mind that we can improve our sleep quality without taking sleeping pills. For instance, exposure to bright light during the day and physical activity can be effective ways to improve sleep.

In the Silver Santé Study, part of our work aims to identify lifestyle factors that may either curb or accelerate the rate of cognitive decline as we age. Among these factors, we are increasingly convinced that sleep may be an important factor to screen in order to prevent cognitive decline and reduce the risk of Alzheimer’s disease. We also suspect that brain training activities such as meditation and foreign language-learning may help to improve sleep quality and to maintain optimum brain structure and function so we look forward to learning more about this and to sharing our results towards the end of the Silver Santé Study.

Sources:

André C, Tomadesso C, Mézenge F, Branger P, De Flores R, Eustache F, Chételat G, Rauchs G. (2017). Age-related NREM-sleep fragmentation: relationships with structural and metabolic brain alterations, amyloid burden and cognitive performance. Alzheimer’s Association International Conference (July 16-20 2017, London, UK).

Branger P, Arenaza-Urquijo EM, Tomadesso C, Mézenge F, André C, de Flores R, Mutlu J, de La Sayette V, Eustache F, Chételat G, Rauchs G. (2016). Relationships between sleep quality and brain volume, metabolism, and amyloid deposition in late adulthood. Neurobiol Aging, 41:107-114. doi: 10.1016/j.neurobiolaging.2016.02.009.

Xie L, Kang H, Xu Q, Chen MJ, Liao Y, Thiyagarajan M, O’Donnell J, Christensen DJ, Nicholson C, Iliff JJ, Takano T, Deane R, Nedergaard M. (2013). Sleep drives metabolite clearance from the adult brain. Science, 342(6156):373-7. doi: 10.1126/science.1241224.