Sleep and Cognition

Sleep is an ancestral and primitive behaviour, an important part of life thought to be essential for restoration of body and mind. As adults, we spend approximately a third of our lives asleep and as we progress through life there are certain shifts in sleep architecture, most notably in sleep quantity. These biological or physiological age-dependent changes in sleep are well documented [1], and alongside the shifts in sleep architecture there is an increased susceptibility to certain sleep disorders. Sleep disturbances and sleep deprivation are common in modern society. Most studies show that since the beginning of the century, populations have been subjected to a steady constant decline in the number of hours devoted to sleep. This is due to changes in a variety of environmental and social conditions (e.g. less dependence on daylight for most activities, extended shift work and 24/7 round-the-clock activities) [2]. Developments in the fields of molecular genetics, behavioural neuroscience, sleep neurobiology, and the cognitive neurosciences have produced converging evidence of a fundamental role for sleep in cognition. Sleep is required for good mental health, and insufficient sleep has negative effects on mood, cognitive performance and motor function [3]. Cognition is a broad term, which encompasses a variety of mental processes including memory, problem solving, language, forward planning and attention, which can all, be differentially affected by inadequate sleep. This can have serious real-life consequences, where many industries including airlines, long-distance truck driving, manufacturing and emergency services have recognised that sleep deprivation has major effects on performance. Epidemiologists and clinical neuroscientists have also documented significant links between degree of sleep disturbance and severity of impairment on selective cognitive functions in a variety of clinical populations, including persons at risk for various dementing illnesses [4, 5]. Sleep disorder, in fact, may be one of the earliest signs of neurodegenerative disorders, including early Alzheimer’s disease (AD) [6]. This chapter will briefly examine the relationship between sleep (quantity and quality) and cognition throughout the life course, and will consider the evidence which suggests that sleep deprivation and sleep disorders are associated with poor cognitive function. More specifically, it will examine the effects that sleep deprivation and sleep disorders have on both amnestic (memory function) and non-amnestic (non-memory function) cognitive processes.