WordNet sense 1 (someone who has exceptional intellectual ability and originality):

genius, mastermind, Einstein, brainiac

WordNet sense 2 (mental ability):

mentality, wit, brainpower, learning ability, mental capacity

WordNet sense 3 (that which is responsible for one's thoughts and feelings; the seat of the faculty of reason):

head, mind, psyche, nous

WordNet sense 4 (that part of the central nervous system that includes all the higher nervous centers; enclosed within the skull; continuous with the spinal cord):

encephalon