AD is marked by significant death of neurons in certain cortical regions and layers in which a particularly vulnerable neuronal phenotype is prevalent. The circuits that are most vulnerable to degeneration are the perforant path, which connects the entorhinal cortex with the hippocampus, and the long corticocortical projections that link association cortices such as inferior temporal cortex and prefrontal cortex (Morrison and Hof, 2002). As these circuits degenerate, there is initially a memory defect from the perforant path degeneration, followed by dramatic loss of cognitive abilities as the corticocortical circuits degenerate. Patients with a moderate memory defect but lacking dementia are often classified as having mild cognitive impairment. These patients have received a great deal of attention because they are the key to understanding the difference between AD and AAMI. Mild cognitive impairment can represent the fairly stable condition of AAMI or the early stage of progressive AD, which will become much more severe over time. As interventions emerge that are appropriate for AD, as opposed to AAMI, this clinical distinction within the mild cognitive impairment group will become of paramount importance.