ABSTRACT

Disturbances in the level of consciousness reflect dysfunction

of either the ascending reticular activating system (ARAS)

(Parvizi and Damasio 2003), the thalamus, or the cortex. The

ARAS is a midline brainstem structure which extends from

the rostral pontine tegmentum up into the mesencephalic

tegmentum, where it lies ventral to the periaqueductal gray

matter. Fibers from the ARAS then extend up into the

thalamus, specifically to the thalamic intralaminar nuclei

and the reticular nucleus, and subsequently fibers from the

thalamus project to the cortex. In addition to this efferent

pathway of the ARAS, there is also a subsidiary, extratha-

lamic pathway, which ascends from the ARAS, and then

passes on through the hypothalamus toward the frontal

cortex.