The earliest neuropathological changes of Alzheimer’s disease, the beta-amyloid plaques, usually appear first in olfactory parts of the brain including the olfactory bulb, anterior olfactory nucleus, and entorhinal cortex. I totally lost my ability to smell several years before I developed any measurable cognitive impairment. Almost all people with Alzheimer’s have at least some impairment of olfaction, but most are not aware of it unless tested, probably because it comes on so gradually.