Figure 3.

Anatomical substratum of arousal and awareness. Consciousness involves two main components: arousal and awareness of oneself and of the environment. Awareness is dependent on the integrity of specific anatomical regions [89]. The ascending reticular activating system (ARAS), the primary arousal structure, is located in the upper pons and lower midbrain in the posterior part of the upper two-thirds of the brainstem [90,91]. A ventral pathway (black solid arrows) projects to the hypothalamus (hypo) and basal forebrain (Bfb); a dorsal pathway (black dashed arrows) projects to the reticular nuclei of the thalamus (thal); and a third pathway (light grey arrows) projects directly into the cortical regions [90]. From the basal forebrain, two main bundles project diffusely to several cortical areas [92]. The reticular nuclei of the thalamus connect to other nuclei in the thalamus. They are involved in a thalamocortical circuit [93] that controls cortical activity. Some regions of the cerebral cortex may also make specific contributions to consciousness [94].