Re: question about alzheimer's disease
Dementia is a broad catagory that includes many types of cognitive decline. Alzheimer is just one of the many types of dementia. Vascular dementia and picks are two other types of dementia.
Depression does not cause dementia. People who are depressed can have some of the same symptoms as those with dementia. Because of their withdrawal they can have behavior changes, difficulty focusing, memory problem etc but the root case is the depression. The correct medication for depression will improve these symptoms. In dementia the symptoms are not improved by depression medication.
Depression is a chemical imbalance in the brain where as dementia is caused by an inability of the synaps of the nerves to function correctly.
As I said before people who have dementia (alzheimer being one type of dementia) may (and often do) develop depression but depression does not cause dementia.
It might help to do a web search on depression, dementia, and alzheimer as Janie suggested.
Good luck and I hope this helped.