FIGURE 1.

A) The potential hierarchical structure of some components of awareness and arousal. B) A conceptual illustration of the potential deterioration in different levels and facets of awareness and arousal with the progression of Alzheimer's disease (AD; colors correspond with categories in [A]). Behavioral evidence suggests components of higher awareness become impaired in mild AD, and awareness generally contracts with disease progression. However, the pattern of impairment is heterogeneous and some aspects of higher awareness may persist in some individuals. Magnetic resonance images of mild (Scheltens 2), moderate (Scheltens 3), and severe AD (Scheltens 4) adapted from Wahlund et al. ⁸