Eat not the Brain
This is the 31st Symbol in the Protreptics of Iamblichus; and the prohibition is very similar to that of Moses forbidding the Jews to eat the blood, because the blood is the life. The brain is the seat of reason and the ruler of the body. It was also esteemed the Divine part—at least, of man.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894