My falang friend is 78, healthy and still functioning but experiencing memory loss  and some confustion.
He is ready to accept some health so any Chiang Mai experience with this is appreciated. 

That seem to be the first signs of dementia. 

But sorry, I cannot give/recommend you the name of a neurologist in CM.

I have some suggestions that may help.

 

There is a neurological hospital connected to Chiang Mai University Medical School. It is on Suthep Road

https://www.cmneuro.go.th/EN/index.php

 

For day to day medical needs, the Geriatric Hospital can be useful

www.med.cmu.ac.th/en/service/excellence-center/gmc/

 

If dementia in some form is diagnosed, then residential care may be needed. Dok Kaew Gardens is attached to McKean Hospital, and is reasonably priced. There are other, less affordable privately owned places.

https://www.mckean.or.th/dok-kaew-gardens/

 

Somebody, somewhere, should be given a power of attorney to manage your friend's affairs. You could perhaps discuss this with him while he is still legally able to make such decisions.

 

Good luck to him and to you.