Nefesh HaChaim (01:14) And thought, it is in the category of the Neshama. She teaches man knowledge and understanding via the holy Torah, and therefore the origin of its abode is in the brain, the tool of thought, and she is the highest category of them all. And so they said in Bereshis Rabbah “She is called by five names...”, “the Neffesh is the blood..., Ruakh..., Neshama is the nature of the creature”— meaning his knowledge and thoughts, as was explained by the Arukh and Rashi.

Lekutei Moharan (61:03) And all these intelligences receive from the comprehensive guiding force, which is the all-encompassing intelligence. This is the soul, which guides all their motions, in the aspect of “the soul from the Almighty enables them to understand” i.e., the soul infuses them with their intelligence. 

Bereishis Rabbah (14:09) The soul has five names: nefesh, neshamah, hayyah, ruah, yehidah. Nefesh is the blood: For the blood is the nefesh. Ruah: this is so called because it ascends and descends: thus it is written, Who knoweth the ruah  of man whether it goeth upwards, and the ruah of the beast whether it goeth downward to the earth  Neshamah is the breath; as people say, His breathing is good. Hayyah: because all the limbs are mortal, whereas this is immortal in the body Yehidah (unique): because all the limbs are duplicated, whereas this is unique in the body.