Think of these as Essential Building Materials. To build brain cells you need fatty acids. Two kinds of fatty acids are considered "essential", which means you must get these from the food you eat. Your body CANNOT produce them. Hence the name Essential Fatty Acids (EFAs).
The first essential fatty acid you need is Alpha-linolenic acid (ALA) or Omega 3. Linseed or Flax if you're American (as pictured) is a fantastic source.
The second essential fatty acid you need is Linoleic acid (LA) or Omega 6. Food sources include sunflower, safflower, corn and sesame oils.