Disruption Of Sleep-Wake Continuum In Dementia And Mild Cognitive Impairment: Macrostructural And Microstructural Findings

The relationship between sleep and cognitive performance (mainly all types of memory) has been supported by recent theories on sleep-related neuronal plasticity (i.e. the hippocampal-neocortical theory and the synaptic downscaling theory). Recent findings suggest that altered sleep/wake activity relates strongly to cognitive impairment and symptoms of dementia. Daytime sleepiness and primary sleep disorders (e.g. insomnia) not only correlate with disturbed cognitive performance (e.g., attention, memory), but they can also be risk factors for cognitive decline and dementia. Concerning, mild cognitive impairment (MCI), which is an intermediate state between normal ageing and dementia, epidemiological data suggest equally disturbed sleep in these patients when compared to patients with dementia, while studies performed with the use of objective tools suggest moderate differences. More specifically, although no major differences in sleep parameters are shown between MCI and demented patients, disturbed sleep in MCI correlates to impaired memory consolidation. Sleep microstructure (e.g. arousals and CAP) in MCI is also compromised. Finally, sleep parameters (e.g., increased napping, decreased slow wave sleep, a more altered sleep microstructure) seem to correlate with a higher risk of MCI progression to dementia, indicating the importance of specific sleep variables as possible biomarkers of disease evolution.