What is happening inside the brain to change behavior?

Often there are behavioral changes associated with Alzheimer’s disease, even in the fairly early stages.
One of the things that is becoming clear is that the hippocampus, where Alzheimer’s begins, is not only important for memory; it also affects anxiety. It is very common to see a patient with early Alzheimer’s disease, sometimes even before they’ve manifested a memory disorder, to be anxious, hyper-reactive and very concerned about things that are going on around them. Sometimes that’s an incredible burden to the caregiver. As the disease progresses, behavior almost always becomes part of what we face. So as a loved one loses their cognitive functions, we often hear about severe anxiety and agitation. Irritability is extremely common in people with Alzheimer’s disease. And as the disease progresses, even things like hallucinations, delusions, or false beliefs become common. Delusions sometimes occur about the loved one and their face. “This is not really my wife, this is an impostor,” they’ll say. And this is extremely hard to manage, and also extremely difficult for caregivers to face. It’s probably the biggest part of the burden of Alzheimer’s disease. It isn’t the memory, per se. It’s these behaviors that emerge.
As the disease progresses, this is almost invariable. It’s the biggest factor in determining caregiver health, and also a huge factor in a family deciding to place their loved one [in a memory care home].