FIGURE 2.

(Left) Consciousness has two main components: arousal, or the level of consciousness, and awareness, corresponding to the contents of consciousness per se. Arousal and awareness are usually positively correlated. However, they involve different brain structures. Arousal involves the activity of subcortical structures encompassing brain-stem reticular formation, hypothalamus, and basal forebrain. Awareness is related to the activity of a widespread set of frontoparietal associative areas, both on the convexity and on the midline. (Right) Awareness can in turn be divided into two main components: self and external awareness. In healthy volunteers, self- and external awareness are usually negatively correlated. Similarly, the frontoparietal awareness network can in turn be divided into two sub-systems, involved in self-and external awareness. Self-awareness networks encompass the posterior cingulate/precuneal cortices, medial frontal cortex, and bilateral temporoparietal junctions. The external awareness network encompasses lateral frontal and parietal cortices. In healthy volunteers, self- and external awareness networks usually show an anticorrelated pattern of activity.