Here’s a suggestion from "The Dinner Choice That Thwarts Alzheimer’s" at RealAge:
Recipe for a sharp mind: chop some mango, jalapeno, and cilantro; toss together with lime juice, salt, and pepper; then spoon generously over grilled fish.
The combo of fatty acids from the fish and antioxidants from the fresh fruit helps protect the brain from dementia.
Other brain foods: nuts, fish (especially wild salmon, whitefish, tilapia, catfish, flounder, mahi mahi), soybeans, tomato juice and spaghetti sauce, olive oil, nut oils, fish oils, flaxseed, avocados, real chocolate (at least 70% cocoa). Read the full article for the explanation of the benefits and recommended amounts.