If you close your eyes and think about it for a while, as philosophers have done for centuries, the world of the mind seems very different from the one inhabited by our bodies. The psychic space inside our heads is infinite and ethereal; it seems obvious that it must be made of different stuff than all the other organs. Cut into the body, and blood pours forth. But slice into the brain, and thoughts and emotions do not spill out onto the operating table. Love and anger cannot be collected in a test tube to be weighed and measured.

René Descartes, the great seventeenth century French mathematician and philosopher, enshrined this metaphysical divide in what came to be known in Western philosophy as mind-body dualism. Many Eastern mystical traditions, contemplating the same inner space, have come to the opposite conclusion. They teach that the mind and body belong to an indivisible continuum.