Walnuts

Walnuts (genus Juglans) are plants in the family Juglandaceae. They are decidours trees. 10 to 40 meters tall. The hard brown walnut shell is covered by a green husk that turns black after falling off.
The walnut kernel possess two lobes that look like abstract butterflies. The lobes are off white in color and sheltered by a thin, light brown skin. They are partially attached to each other. The kernels are enclosed in round or oblong shells that are brown in color, rough and hard from outside.
Walnut nutrition
Walnuts are the best source of omega-3 fatty acids, a special type of fat that is essential for our bodies, but that the body cannot make.

Walnuts are often known as a "brain food," not only because of the wrinkled brain-like appearance of their shells, but since they high concentration of omega-3 fats. For your brain cells to function properly, this structural fat needs to be primarily the omega-3 fats found in walnuts and cold-water fish.
The cell membranes of our body including the neurons in our brain are composed of fats. They are the gate keepers to allow certain things and disallow others into the cell. Omega 3 is especially a fluid which makes the whole process a lot easier, thus maximized the cells ability to promote nutrients and eliminating wastes, a good way to keep them away.