ABSTRACT
Transitions from wakefulness to sleep, or between non-rapid eye movement (NREM) and rapid eye movement (REM) sleep, are characterized by changes in behaviour, subjective experience and physiology. However, these changes do not always occur in lockstep, and the study of both healthy and pathological sleep has revealed many instances of dissociations between the behavioural, experiential and physiological dimensions of sleep. These dissociations do not fit with the classical vision of wakefulness, NREM and REM sleep as global all-or-nothing events. We argue here that considering sleep as both a global and local phenomenon can address these challenges. First, we will review the evidence in animals and humans, healthy and pathological brains, stressing the existence and relevance of local regulations of sleep. Second, we will synthesize the impact of these local modulations on behaviour, cognition and subjective experience. We will examine how the notion of local sleep sheds new light on a wide range of atypical phenomena in wakefulness and sleep such as dreaming in NREM sleep, intra-sleep responsiveness or inattention and mind wandering in wakefulness. This local view of sleep also offers an interesting framework to better understand sleep disorders. However, this new vision of sleep opens many new questions on the origins, mechanisms and possible functions of local aspects of sleep.
