Norman Doidge on Rene Descartes

 “We have seen that imagining an act engages the same motor and sensory programs that are involved in doing it. We have long viewed our imaginative life with a kind of sacred awe: as noble, pure, immaterial, and ethereal, cut off from our material brain. Now we cannot be so sure about where to draw the line between them. Everything your “immaterial” mind imagines leaves material traces. Each thought alters the physical state of your brain synapses at a microscopic level. Each time you imagine moving your fingers across the keys to play the piano, you alter the tendrils in your living brain. These experiments are not only delightful and intriguing, they also overturn the centuries of confusion that have grown out of the work of the French philosopher René Descartes, who argued that mind and brain are made of different substances and are governed by different laws. The brain, he claimed, was a physical, material thing, existing in space and obeying the laws of physics. The mind (or the soul, as Descartes called it) was immaterial, a thinking thing that did not take up space or obey physical laws. Thoughts, he argued, were governed by the rules of reasoning, judgment, and desires, not by the physical laws of cause and effect. Human beings consisted of this duality, this marriage of immaterial mind and material brain. But Descartes—whose mind/body division has dominated science for four hundred years—could never credibly explain how the immaterial mind could influence the material brain. As a result, people began to doubt that an immaterial thought, or mere imagining, might change the structure of the material brain. Descartes’s view seemed to open an unbridgeable gap between mind and brain. His noble attempt to rescue the brain from the mysticism that surrounded it in his time, by making it mechanical, failed. Instead the brain came to be seen as an inert, inanimate machine that could be moved to action only by the immaterial, ghostlike soul Descartes placed within it, which came to be called “the ghost in the machine.” By depicting a mechanistic brain, Descartes drained the life out of it and slowed the acceptance of brain plasticity more than any other thinker. Any plasticity—any ability to change that we had—existed in the mind, with its changing thoughts, not in the brain. But now we can see that our “immaterial” thoughts too have a physical signature, and we cannot be so sure that thought won’t someday be explained in physical terms. While we have yet to understand exactly how thoughts actually change brain structure, it is now clear that they do, and the firm line that Descartes drew between mind and brain is increasingly a dotted line.” 

Norman Doidge, The Brain That Changes Itself: Stories of Personal Triumph from the Frontiers of Brain Science