heart or brain

Why was it we started to think with our 'heart' not 'brain'? Egyptians thought the brain was not important and removed it completely in mummification process while preserving the other vital organs inside jars guarded by their gods. And the idea that a person's heart will be as light as a feather if his deeds are justfied is anohter manifestation of the importance of THE HEART. Or was it because the heart beats n throbs that they took notice while on the other hand, brain lies peacefully as a stagnant mass inside the thick enclosure of the skull... Whatever, 'lemme show you my true brain' sounds weird enough, not to say 'lemme show u the true colour my brain'. I don't wanna know.