Yes in Alzheimer's it appears the brain is starving for fuel (and areas dying because of it) even though it is swimming in glucose. Insulin resistance of the brain cells. There has been good results of people being given exogenous ketones and the brain responds positively with some cognition reversal. The use of ketones doesn't seem to be effected, only glucose. Of course the brain cells that are actually dead it can't help, but the ones just in the starving stage it does seem to reverse and get better.

I have linked to Mary Newport many times and her husbands improvement in Alzheimer's cognition by feeding him coconut oil and later when it became available MCT oil. The medium chain triglycerides are readily converted into ketones by the liver.

https://www.youtube.com/watch?v=A3uQ85noslk&pp=ygUaYWx6aGVpbWVycyBhbmQgY29jb251dCBvaWw%3D

Edit: The above is an outstanding interview. Anybody remotely interested in dementia should listen to it. It is first of a several part series.
Part 2
Full playlist.