He gave three lines of reasoning, based on brain surgery on over a thousand patients:
Michael Egnor points out that Penfield offered three lines of evidence: His inability to stimulate intellectual thought during brain operations, the inability of seizures to cause intellectual thought, and his inability to stimulate the will. … So he concluded that the intellect and the will are not from the brain. Which is precisely what Aristotle said. Mind Matters News
See also: Pioneer neuroscientists believed the mind is more than the brain. A number of them were Nobel Laureates and their views were informed by their work. In a podcast discussion with Walter Bradley Center director Robert J. Marks, neurosurgeon Michael Egnor talks about how many famous neuroscientist became dualists—that is, they concluded that there is something about human beings that goes beyond matter—based on observations they made during their work.
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Four researchers whose work sheds light on the reality of the mind The brain can be cut in half, but the intellect and will cannot, says Michael Egnor. The intellect and will are metaphysically simple