Two Aspects of Impaired Consciousness in Alzheimer's Disease

Alzheimer's disease (AD) is a degenerative dementia characterized by different aspects of impaired consciousness. For example, there is a deficit of controlled processes that require conscious processing of information. Such an impairment is indexed by decreased performances at controlled cognitive tasks, and it is related to reduced brain metabolic activity in a network of frontal, posterior associative, and limbic regions. Another aspect of impaired consciousness is that AD patients show variable levels of anosognosia concerning their cognitive deficits. A discrepancy score between patient's and caregiver's assessment of cognitive functions is one of the most frequently used measures of anosognosia. A high discrepancy score has been related to impaired activity in the superior frontal sulcus and the parietal cortex in AD. Anosognosia for cognitive deficits in AD could be partly explained by impaired metabolism in parts of networks subserving self-referential processes (e.g., the superior frontal sulcus) and perspective-taking (e.g., the temporoparietal junction). We hypothesize that these patients are impaired in the ability to see themselves with a third-person perspective (i.e., being able to see themselves as other people see them).