Here is a pretty awesome video. I've summarized some of the key points below if you don't want to watch. Very interesting.
"What foods make my brain work best?" by Seth Roberts, PhD from Ancestral Health Society on Vimeo.
He started taking flax seed oil every day. Worked up to 4 tablespoons. Found that his balance increased. Tried other types including Olive oil. Didn't have the same effect. When he quit the flax seed balance got worse. He also found out that his gums improved dramatically. This was also documented by other people that had similar experiences.
Found that pork belly fat improved sleep quality, duration and speed at which he fell asleep. He had more energy the next day.
Stumbled upon butter and found that 4 tablespoons a day improved his arithmetic testing.
Addressed the belief that although possibly helping cognition, he was killing his cardiovascular health. (butter is bad for your arteries/heart) By chance he had taken an Agatson test before all the butter. It was 38. One year later, after eating 4tb of butter a day, the Agatson test was now a 29. Most people get worse by 20% per year.
Big improvement in brain function is possible, and often the the brain dysfunction is invisible. Improvements in other systems as such as inflammation, circulatory are possible as well.