As the brain gets older, our blood vessels and thus the cells they support start to degenerate. The result is often more than just be forgetful (which is a sign of high intelligence!), perhaps into dementia and Alzheimer’s disease.
This video (4:41) discusses the results of research that show that Hyperbaric Oxygen Therapy expands the blood vessels and helps them regenerate. He speaks with a tough accent, but this is short and well worth listening to if you are old like me or have older people in your life.