How might atrophy or hardening of the brain associated with Alzheimer's affect cognitive functioning

Alzheimer’s disease (AD) is a progressive, degenerative brain disease that slowly erodes memory and thinking skills, and eventually even the ability to carry out simple tasks. It is the most common cause of dementia, accounting for approximately 50-70% of all cases of dementia. The incidence of AD rises exponentially with advancing age. Estimates vary, but experts suggest that as many as 5.1 million Americans may have Alzheimer’s. The greatest risk for Alzheimer’s disease is advancing age, with the risk increasing as we get older