The reality of man is his thought, not his material body. The thought force and the animal force are partners. Although man is part of the animal creation, he possesses a power of thought superior to all other created beings. – Abdu’l-Baha, Paris Talks, pp. 17-18.
Why not material body?
In Europe I told the philosophers and scientists of materialism that the criterion of the senses is not reliable. For instance, consider a mirror and the images reflected in it. These images have no actual corporeal existence. Yet if you had never seen a mirror, you would firmly insist and believe that they were real. The eye sees a mirage upon the desert as a lake of water, but there is no reality in it. As we stand upon the deck of a steamer, the shore appears to be moving, yet we know the land is stationary and we are moving. The earth was believed to be fixed and the sun revolving about it, but although this appears to be so, the reverse is now known to be true. A whirling torch makes a circle of fire appear before the eye, yet we realize there is but one point of light. We behold a shadow moving upon the ground, but it has no material existence, no substance … In brief, the senses are continually deceived, and we are unable to separate that which is reality from that which is not. – Abdu’l-Baha, The Promulgation of Universal Peace, p. 21.
How about the Human Brain or intelligence
If a man’s thought is constantly aspiring towards heavenly subjects then does he become saintly: if on the other hand his thought does not soar, but is directed downwards to centre itself upon the things of this world, he grows more and more material until he arrives at a state little better than that of a mere animal. – Ibid., pp. 17-18