Wilder Penfield was a pivotal figure in modern neurosurgery. He was an American-born neurosurgeon at the Montreal Neurological Institute who pioneered surgery for epilepsy. He was an accomplished scientist as well as a clinical surgeon, and made seminal contributions to our knowledge of cortical physiology, brain mapping, and intra-operative study of seizures and brain function under local anesthesia with patients awake who could report experiences during brain stimulation.There's more at the link. Egnor's argument boils down to this. If the material brain is sufficient to account for all of our cognitive experience, and since stimulation that normally triggers all sorts of "mental" activity never triggers abstract thinking, abstract thinking must arise from something other than the material brain.
His surgical specialty was the mapping of seizure foci in the brain of awake (locally anesthetized) patients, using the patient's experience and response to precise brain stimulation to locate and safely excise discrete regions of the cortex that were causing seizures. Penfield revolutionized neurosurgery (every day in the operating room I use instruments he designed) and he revolutionized our understanding of brain function and its relation to the mind.
Penfield began his career as a materialist, convinced that the mind was wholly a product of the brain. He finished his career as an emphatic dualist.
During surgery, Penfield observed that patients had a variable but limited response to brain stimulation. Sometimes the stimulation would cause a seizure or evoke a sensation, a perception, movement of muscles, a memory, or even a vivid emotion. Yet Penfield noticed that brain stimulation never evoked abstract thought. He wrote:There is no area of gray matter, as far as my experience goes, in which local epileptic discharge brings to pass what could be called "mindaction"... there is no valid evidence that either epileptic discharge or electrical stimulation can activate the mind... If one stops to consider it, this is an arresting fact. The record of consciousness can be set in motion, complicated though it is, by the electrode or by epileptic discharge. An illusion of interpretation can be produced in the same way. But none of the actions we attribute to the mind has been initiated by electrode stimulation or epileptic discharge. If there were a mechanism in the brain that could do what the mind does, one might expect that the mechanism would betray its presence in a convincing manner by some better evidence of epileptic or electrode activations.[italics mine]The brain was necessary for abstract thought, normally, but it was not sufficient for it. Abstract thought was something other than merely a process of the brain.
Why don't epilepsy patients have "calculus seizures" or "moral ethics" seizures, in which they involuntarily take second derivatives or contemplate mercy? The answer is obvious -- the brain does not generate abstract thought. The brain is normally necessary for abstract thought, but not sufficient for it.
Thus, the mind, as Penfield understood, can be influenced by matter, but is, in its abstract functions, not generated by matter.
This is not proof that there's a mind, of course, but it is certainly consistent with the dualist hypothesis that we are a composite of mind and brain and certainly puzzling on the materialist hypothesis that the material brain is solely responsible for all of our mental experience.