In the 9th chapter the old rebbe explains about the animalistic soul: the animalistic soul is in the left side of the heart which is full of blood. So just like the blood comes from the heart and spreads to all limbs including the head, so the animalistic soul which causes anger and all other bad characters is in the heart and from the heart the bad characters spread to the brain, and then the person thinks about them. But all good characters come from the G-dly soul which is in the brain and right side of the heart in the part which has no blood, and from there they spread to the heart and all other limbs, because when one thinks about the greatness of G-d, he will start to love G-d, and so are all holy feelings.