APP and Alzheimer disease: The role of dopamine (DA) dysfunction in Alzheimer's disease has been investigated in a mouse model expressing a mutated version of the human amyloid precursor protein: neuronal loss in the ventral tegmental area (VTA), but not in the substantia nigra, anticipated alterations in hippocampal neuron function and memory performance.7,8 Additional findings have emerged from studies carried out on cognitively unimpaired (CU) older adults and people with Alzheimer's disease.