Remarkably, neuroscience tells us three things about the mind: the mind is metaphysically simple, the intellect and will are immaterial, and free will is real.
In the middle of the twentieth century, neurosurgeons discovered that they could treat a certain kind of epilepsy by severing a large bundle of brain fibers, called the corpus callosum, which connects the two hemispheres of the brain. Following these operations, each hemisphere worked independently. But what happened to the mind of a person with his or her brain split in half?
The neuroscientist Roger Sperry studied scores of split-brain patients. He found, surprisingly, that in ordinary life the patients showed little effect. Each patient was still one person. The intellect and will – the capacity to have abstract thought and to choose – remained unified. Only by meticulous testing could Sperry find any differences: their perceptions were altered by the surgery. Sensations – elicited by touch or vision – could be presented to one hemisphere of the brain, and not be experienced in the other hemisphere. Speech production is associated with the left hemisphere of the brain; patients could not name an object presented to the right hemisphere (via the left visual field). Yet they could point to the object with their left hand (which is controlled by the right hemisphere). The most remarkable result of Sperry’s Nobel Prize–winning work was that the person’s intellect and will – what we might call the soul – remained undivided.
The brain can be cut in half, but the intellect and will cannot. The intellect and will are metaphysically simple.
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