https://www.medscape.com/viewarticle/894022?nlid=121314_329&src=WNL_mdplsnews_180316_mscpedit_psyc&uac=27343DV&spon=12&impID=1583202&faf=1

Basically, there is not solid evidence to the myth that ECT causes dementia or permanent memory decline.
It’s the depression itself that causes brain degeneration like Alzheimers (i.e. DOD, dementia of depression).
Duration of depression, untreated, determines these changes.

https://www.medscape.com/viewarticle/893762?nlid=121314_329&src=WNL_mdplsnews_180316_mscpedit_psyc&uac=27343DV&spon=12&impID=1583202&faf=1

These studies show brain changes in chronic depression due to inflammation