APP and Alzheimer disease: Neurological disorders such as mild cognitive impairment (MCI) and Alzheimer’s disease (AD) are characterized by changes in the function of cholinergic neurons; cholinergic neuron activity may be enhanced initially due to synaptic plasticity, followed by loss of function of these neurons related at least in part to the toxic effects of β-amyloid peptides (Aβ) that are produced by cleavage of amyloid precursor protein (APP)5, 6, 7.