You are allowed to mix things up here @rharphelle. This is a very efficient way to learn things! You see, when someone with dementia dies and have their brain examined, there will be many physical signs : plaques, tangles, atrophy. You can actually see them. This is why we say it is a disease of the brain.

However, when someone who, let's say, has been severely depressed for years, dies. If his post-mortem brain is examined, there won't be a single physical evidence showing that individual suffered from depression. This is why we say it is a disease of the mind.

Well, you sure are on your way to your "Steemit Psychology Degree" my dear 😘