Brain imaging technologies -- positron emission tomography, MRIs, and near infrared spectroscopy -- have reached a point of development that bioethicists are discussing the moral implications of being able to read someone's mind (see Science, March 11, 2005).
It can be unnerving to see those colorful images in the science journals of brains flickering with activity as subjects do mathematics, read poetry, or think about God. Mental states studied by brain imaging include intelligence, racial antipathy, impulsivity, additive cravings, political affiliations, sexual attraction, neuroticism, aggression, moral reasoning, empathy, deception and religious transcendence.
In other words, all of those characteristics that used to be ascribed to an immaterial soul -- the ghost in the machine -- are now seen to be identifiable activities of the machine itself. Descartes turned on his ear: I am, therefore I think.