Prabhupada: The modern scientific theory that the brain substance is the cause of all intelligent work is not valid. The brain substance of Daksa and that of a goat are different, but Daksa still acted like himself, even though his head was replaced by that of a goat. The conclusion is that it is the particular consciousness of an individual soul which acts. The brain substance is only an instrument which has nothing to do with real intelligence. The real intelligence, mind and consciousness are part of the particular individual soul. It will be found in the verses ahead that after Daksa's head was replaced by the goat's head, he was as intelligent as he had previously been. He prayed very nicely to satisfy Lord Siva and Lord Visnu, which is not possible for a goat to do. Therefore it is definitely concluded that the brain substance is not the center of intelligence; it is the consciousness of a particular soul that works intelligently. The whole movement of Krsna consciousness is to purify the consciousness. It doesn't matter what kind of brain one has because if he simply transfers his consciousness from matter to Krsna, his life becomes successful. It is confirmed by the Lord Himself in Bhagavad-gita that anyone who takes up Krsna consciousness achieves the highest perfection of life, regardless of whatever abominable condition of life he may have fallen into. Specifically, anyone in Krsna consciousness goes back to Godhead, back to home, on leaving his present material body. --- Ref. => SB 4.7.5.