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Pioneering Neuroscientist Wilder Penfield: Why Don’t We Have Intellectual Seizures?


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 intraoperative study of seizures and brain function under local anesthesia with patients awake who could report experiences during brain stimulation.

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.1 [Emphasis added.]

Penfield noted that intellectual function — abstract thought — could only be switched off by brain stimulation or a seizure, but it could never be switched on in like manner. 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.

Penfield’s observations bring to light a perplexing aspect of epilepsy — or at least an aspect of epilepsy that should be perplexing to materialists. Seizures always involve either complete unconsciousness or specific activation of a non-abstract neurological function — flashes of light, smells, jerking of muscles, specific memories, strong emotions — but seizures never evoke discrete abstract thought. This is odd, given that the bulk of brain tissue from which seizures arise is classified as association areas that are thought to sub-serve abstract thought. 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.

Furthermore, Penfield noted that patients were always aware that the sensation, memory, etc., evoked by brain stimulation was done to them, but not by them. Penfield found that patients retained a “third person” perspective on mental events evoked by brain stimulation. There was always a “mind” that was independent of cortical stimulation:

The patient’s mind, which is considering the situation in such an aloof and critical manner, can only be something quite apart from neuronal reflex action. It is noteworthy that two streams of consciousness are flowing, the one driven by input from the environment, the other by an electrode delivering sixty pulses per second to the cortex. The fact that there should be no confusion in the conscious state suggests that, although the content of consciousness depends in large measure on neuronal activity, awareness itself does not.2

Penfield finished his career as a passionate dualist. His materialist naiveté did not survive his actual scientific work and his experiences as a clinical neurosurgeon. My own experience as a neurosurgeon has led me to the same conclusion.

Remarkably, scholastic philosophers who worked in the Aristotelian tradition presaged Penfield’s observations centuries ago. In the classical Aristotelian-Thomist understanding, the mind is several powers of the soul, which is the subsistent form of the body. “Subsistent” means that the soul informs the body, so to speak, as any form is composed to matter, but that it can exist independently of matter. The reason it can exist independently of matter is that the intellectual powers of the soul — the ability to contemplate universals and engage in abstract thought — is necessarily an immaterial power. Universals — concepts that are not particular things — by their nature cannot be in particular things, and thus cannot be in matter, even in brain matter.

Thus, the mind, as Penfield understood, can be influenced by matter, but is, in its abstract functions, not generated by matter.

Aristotle, if informed of Penfield’s experiments, would have yawned: “Of course the mind is not wholly material. Abstract thought — contemplation of universals — is immaterial by its nature, and cannot be generated by the brain.” The philosopher would have shrugged, as he concerned himself with other propositions that weren’t as obvious. It is remarkable that insights from philosophers in the Aristotelian-Thomist school from millennia ago presage modern discoveries in the neuroscience of the mind-brain relationship with such stunning accuracy.

H/t: Chris Carter, Science and the Near-Death Experience: How Consciousness Survives Death.


(1) Penfield, The Mystery of the Mind, pp. 77-8.

(2) Ibid., p. 55.

Image: Wilder Penfield in 1913 as a student at Princeton, by Bain News Service [Public domain], via Wikimedia Commons.

Michael Egnor

Professor of Neurosurgery and Pediatrics, State University of New York, Stony Brook
Michael R. Egnor, MD, is a Professor of Neurosurgery and Pediatrics at State University of New York, Stony Brook, has served as the Director of Pediatric Neurosurgery, and is an award-winning brain surgeon. He was named one of New York’s best doctors by the New York Magazine in 2005. He received his medical education at Columbia University College of Physicians and Surgeons and completed his residency at Jackson Memorial Hospital. His research on hydrocephalus has been published in journals including Journal of Neurosurgery, Pediatrics, and Cerebrospinal Fluid Research. He is on the Scientific Advisory Board of the Hydrocephalus Association in the United States and has lectured extensively throughout the United States and Europe.