Forebrain and Hindbrain Inhibition of the Reticular Activating System
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Arousal may be seen as having two components: ascending and descending. Ascending activation engages cortical processes for conscious, cognitive (psychological) arousal and the subsequent behavioral adjustments appropriate to the conditions that initiated the arousal. The descending component may be described as physiological activation in which the somatic motor system and the sympathetic component of the autonomic nervous system produce a complex of changes to support the increased activity that normally occurs during waking. It was recognized in the 1950s that both the ascending (psychological) and descending (physiological) components of arousal had elements of positive feedback to the brain stem arousal system. A number of workers in the UCLA group, as well as others, demonstrated that stimulation of certain cortical sites produced cortical arousal (Segundo et al. 1955a,b; Adey et al., 1957; Kaada and Johannessen, 1960). This effect was shown to be mediated by a corticoreticular influence that activated the ARAS; that is, the cortex does not possess the ability to arouse it-self without the mediation of the ARAS. An everyday understanding of this corticoreticular influence would be the increased arousal produced by the daydreaming of stimulating thoughts.
KeywordsReticular Formation Carotid Sinus Inhibitory Influence Cortical Arousal Somatic Motor
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