I just wanted to give you a new thought. What if our brain really only regulates like heart beat, blood flow, physical things and we have a totally different part of us that is how we feel, our emotions, personality, our thoughts, who we are. Lets say it is the soul. What if all our brain function was completely knocked out -all memory (this has happened to me by the way) and yet we found we were still able to function with all this brain damage. We could be not depressed, able to feel emotions and think about new and expanded ideas. You are locking yourself in to an obsession my friend. Brain shrinkage? I have a 3mm area of my brain that is receiving no signals. It is shown on MRI. Yet I somehow am okay. Not functioning as actively as I used to but still ok. I also have brain shrinkage that shows on the frontal lobe. Yes I have to take some medications but I am able to MANAGE the condition. You know Einstein proved what I said above about having a separate part that is really us and can function without the brain.
Try to learn to meditate and expand your thinking past these thoughts. When these thoughts come in chuck them out fast just like you would smelly garbage in your house. Picture in your mind you throwing this thought out and every time it comes in chuck it out and think about something positive. You can change your thinking. You have the power. Not your brain. You are the master make your brain behave. Take charge of it. It works for you.
Good luck. I hope this gives you a different perspective.
Brain