Physiological Changes in the Autonomic Nervous System During Sleep

A behavioral state can be defined as the set of values that describe the level of activity of the physiological variables at a given point in time. Accordingly, each behavioral state is characterized by a specific pattern of autonomic nervous system (ANS) activity. The ANS, working together with the somatomotor and the neuroendocrine system, allows the body to maintain its internal homeostasis, as well as to optimize the interaction between the organism and the external environment. Since wakefulness and sleep are behaviors characterized by different levels of activity and interaction with the external environment, it is unsurprising that a consistent remodulation of ANS activity occurs during the transition from wakefulness to sleep. Furthermore, sleep itself is a state showing an intrinsic heterogeneity. In fact, in non-rapid eye-movement sleep (NREMS), as well as during quiet wakefulness, physiological adjustments work effectively to maintain stable internal conditions (i.e., maintenance of body homeostasis); in contrast, during rapid eye-movement sleep (REMS) the regulatory control of physiological variables follows an apparently “non-homeostatic” modality that has been defined as “poikilostatic”. The ANS regulates the majority of the body’s internal processes (e.g., blood pressure, cardiac activity, breathing, and body temperature) via afferent visceral and efferent sympathetic and parasympathetic pathways. Given the functional dichotomy in terms of control theory between NREMS and REMS, the ANS activity changes dramatically even across sleep stages.