“…There have been suggestions that a possible bidirectional relationship exists between alterations in sleep rhythm and the development of dementias {particularly Alzheimer disease (AD)} ( Ju et al, 2014;Guarnieri and Sorbi, 2015;Villa et al, 2015;Urrestarazu and Iriarte, 2016). This is based on the facts that; a) changes in sleep have been observed to predate the onset of cognitive symptoms in patients with dementia (AD), with a decline in sleep quality and/or circadian function occurring in parallel with both cognitive dysfunction and the progression of disease (see Ju et al, 2014 for review) .b) sleep disturbances and disruption of the neural regulation of the sleep-wake rhythm appear to be involved in the cellular and molecular mechanisms of cognitive decline (Guarnieri and Sorbi, 2015), and have been associated with severity of memory and cognitive impairment (Shin et al, 2014), c) alteration in sleep rhythm has a significant impact on physical, physiologic and cognitive functioning in individuals with dementias and are positively associated with the severity of behavioural dysfunction and cognitive impairment (Guarnieri and Sorbi, 2015). Studies have also reported that the concentrations of amyloid-β (Aβ) have a diurnal variation, with levels rising during wakefulness and the nadir during sleep (Huang et al, 2012;Lucey and Bateman, 2014); there are also reports that sleep facilitates Aβ clearance, a function which may be impaired with sleep disturbance ( Ju et al, 2014;Miller, 2015).…”