To Increase Our Knowledge on Sleep, Sleep Disorders, and Chronobiology in the Neuroscience Field during the Next Decade

The Grand Challenge for Sleep and Chronobiology in the Neurology/Neuroscience domains for the twenty-first century is to improve our understanding of the complex relationships between sleep, wake, and chronobiology in healthy subjects and in patients with neurological disorders. Sleep disorders are very common and often disabling conditions that can be isolated or associated with neurological disorders. basic scientists also are involved in sleep disorder diagnosis and research. This corresponds to a heterogeneous group of physicians/researchers with different interests and expertise that include basic and clinically applied research. Our diversity of interests is both our strength and a challenge. Sleep is a universal physiological need that plays a key role in the prevention of health problems. In modern life, sleep disruption through behavioral deprivation is a major issue. Indeed, one-third of the population is affected by sleep disorders, as defined by the revised International Classification of Sleep Disorders (1), namely insomnia, central hypersomnolence disorders (such as narcolepsy), sleep-related movements disorders (such as restless legs syndrome), sleep-related breathing disorders , parasomnias (such as sleepwalking and REM-sleep behavior disorder), and circadian rhythm sleep–wake disorders. Epidemiological studies have demonstrated the large prevalence of many sleep disorders in the general population, especially in patients with neurological and psychiatric diseases, and their association with a decline of cognitive performance, productivity, and quality of life, with a major social, medical, and economic impact. People with sleep disorders are often at risk of accidents, psychiatric, neurological and cardiovascular diseases, obesity, and metabolic disorders, for example, sleep-disordered breathing, excessive daytime sleepiness, short and long sleeping time are risk factors for cardiovascular diseases; insomnia for depression; REM-sleep behavior disorder for Parkinsonism, etc. In addition, sleep–wake alterations (e.g., reduced slow wave sleep and circadian disturbances) may influence the course and outcome of neurodegenerative diseases, such as Alzheimer's disease (2). Narcolepsy with cataplexy remains the classic example of neurological sleep disorder and one of the most studied sleep disorders at the molecular level. Narcolepsy is a disabling disorder characterized by excessive daytime sleepiness and abnormal rapid-eye-movement sleep manifestations, including cataplexy (sudden loss of muscle tone triggered by strong emotions), sleep paralysis, hypnagogic hallucinations, and sleep onset REM periods (3). Narcolepsy with cataplexy has been renamed narcolepsy type 1 due to the deficiency in hypocretin signaling caused by the selective loss of hypothalamic hypocretin neurons. Conversely, no other specific reliable biomarker has been described so far for most of the other sleep disorders.