Elementary CNS arousal

Abstract

Diffusely projecting, global controls over brain arousal have long been recognized in clinical neurology, as their damage leads to disorders of consciousness. In the first half of the twentieth century, brain arousal was thought to be triggered and maintained by the influx of sensory information. This viewpoint was superseded by two relevant lines of research that developed in relative isolation. One involved the ascending reticular activating system, a system which comprises neuronal cell bodies in the brainstem reticular formation that have diffuse ascending axonal projections to the forebrain, including the central thalamus, and which play a key role in modulating levels of arousal and attention. The other system involves hypothalamic centers involved in controlling the expression of both sleep and motivated or goal-oriented behaviors essential for the survival of the individual (e.g., appetitive behaviors associated with hunger and thirst) and survival of the species as a whole (e.g., sexual and parental behaviors).