If a caregiver is doing self-care and proper interventions for dementia will their loved one's cognition improve some?

When you say self-care, do you mean that you are caring for the person with dementia yourself? It's just that we usually use self-care to describe taking care of ourselves, i.e. not allowing ourselves to get run down and burned out as caregivers.

You can't - depending on the cause of it anyway: there are reversible causes of dementia but they are comparatively rare and usually spotted by doctors - reverse the process of dementia. Even those therapies which are intended to halt or significantly slow it are coming in for increasingly loud criticism (of their efficacy).

But what you can do through interventions, adaptations and skilled support is lessen the *impacts* of dementia very significantly indeed, and for some time. And if you've just stepped in to help somebody who was having real trouble, you will probably have made a huge improvement in that person's daily quality of life.

Would you like to say more about what is happening in your situation?

Dementia is a process of physical decline; so, although you may be able to somewhat ameliorate your loved one's symptoms, you cannot---barring some miracle medication I'm unaware of---improve their cognition because you can't affect any of the underlying mechanisms producing it. Dementia actually kills parts of the brain.

I've noticed with my mother (Vascular Dementia) that she has good days and bad. It's like she has a short in her brain where a connection is sometime, for some unknown reason, made, and she can think relatively clearly. But it always gets progressively worse.

What are you doing that you feel will improve the person's cognition? We can't answer the question without more info.