Rationale for focus on the tongue musculature

The tongue is a moveable mass of muscular tissue that is attached to the floor of the mouth (Fig. 1). The tongue is the organ of taste, aids in the mastication and swallowing of food as well as contributing to effective ventilation by keeping the pharyngeal airspace open to allow for the effective passage of air into the lungs. The respiratory function of the tongue can be compromised during sleep as a consequence of the naturally occurring changes in brain state that lead to changes in the neural and chemical inputs to the hypoglossal motor pool, the source of motor output to the muscles of the tongue. Ingestion of commonly used drugs can also change the neural and chemical inputs to the hypoglossal motor pool, so also influencing the ability of the tongue to keep the upper airway open for effective breathing. Examples of such commonly used drugs that influence brain chemistry include anaesthetics, sedative hypnotics and ethanol, all of which can also significantly influence tongue muscle activity and can impair breathing in some individuals. Such agents can exert their influences on tongue muscle activity via direct actions on key components of the respiratory network, including the hypoglossal motor pool, as well as the state-dependent neural inputs that modulate hypoglossal motor activity as a function of changes in sleep-wake states. This paper reviews the control of the tongue during sleep by state-dependent neuromodulators. The tongue and its control by sleep state-dependent modulators