A Map of the Soul

“Doctor, what’s that sound?”

The voice startled me. I was performing brain surgery on a woman with a tumor near the area that controls speech. I was removing much of her frontal lobe, in order to remove the tumor. To map her speech area with an electrical probe, I needed her to be awake. So I performed the surgery under mild local sedation only. The brain itself feels no pain.

It took me a moment to realize that it was my patient, not a nurse, speaking to me from under the surgical drapes. “Just the sound of the instruments,” I replied, not entirely candid. The sound was a lot of her frontal lobe going up my sucker into a canister.

“It’s loud,” she said, half-laughing from nervousness and a sedative. “How’s the operation going?”

“Fine. Everything’s going well. How do you feel?”

“OK. Sleepy. It doesn’t hurt.”

We chatted as I worked. She was drowsy, but quite coherent. She went on to recover nicely. Her tumor had been benign, and her prognosis was good.

Francis Crick, neuroscientist and co-discoverer of the helical structure of DNA, expressed the widespread view that the mind is a function of material stuff: “A person’s mental activities are entirely due to the behavior of nerve cells, glial cells, and the atoms, ions, and molecules that make them up and influenced them.” How, then, is it possible to converse with someone while removing the large portions of her brain that serve thought and reasoning?

I’m a neuroscientist and professor of neurosurgery. The mind-brain question haunts me. Neurosurgeons alter the brain on a daily basis, and what we find doesn’t fit the prevailing view that the brain runs the mind as computer hardware runs software.

I have scores of patients who are missing large areas of their brains, yet who have quite good minds. I have a patient born with two-thirds of her brain absent. She’s a normal junior high kid who loves to play soccer. Another patient, missing a similar amount of brain tissue, is an accomplished musician with a master’s degree in English.

How can this be? It wasn’t until I read Thomas Aquinas that I began to understand.

Aquinas began by reaching back to an earlier thinker. Following Aristotle, he posited that the human soul has three kinds of powers. It has vegetative powers, which serve physiological functions such as heartbeat, respiration, and metabolism. It has sensitive powers, such as sensation, perception, memory, sensitive appetite, and locomotion. The vegetative and sensitive powers are caused by matter, in a purely physical way.

But the human soul also has intellect and will, powers of a wholly different kind. With our intellect, we can think of universal concepts, such as mercy and justice and abstract mathematics. With our will, we can act on abstract principles. Because thinking of abstract concepts entails thoughts removed from particular things, Aquinas reasoned, intellect couldn’t be a material thing. Intellect and will are immaterial powers.

Aquinas taught that our soul’s immaterial powers are only facilitated by matter, not caused by it, and the correlation is loose. His insight presaged certain findings of modern neuroscience.

Wilder Penfield, an early-twentieth-century neurosurgeon who pioneered seizure surgery, noted that during brain stimulation on awake patients, he was never able to stimulate the mind itself—the sense of “I”—but only fragmented sensations and perceptions and movements and memories. Our core identity cannot be evoked or altered by physical stimulation of the brain.

Relatedly, Penfield observed that spontaneous electrical discharges in the brain cause involuntary sensations and movements and even emotions, but never abstract reasoning or calculation. There are no “calculus” seizures or “moral” seizures, in which patients involuntarily take second derivatives or ponder mercy.

Similar observations emerge from Roger Sperry’s famous studies of patients who had undergone surgery to disconnect the hemispheres of the brain. This was done to prevent seizures. The post-operative patients experienced peculiar perceptual and behavioral changes, but they retained unity of personal identity—a unified intellect and will. The changes Sperry discovered in his research (for which he won a Nobel Prize) were so subtle as to pass unnoticed in everyday life.

In the past decade, British researcher Adrian Owen has found using fMRI imaging that some patients with such severe brain damage that they are considered to be in a persistent vegetative state are actually capable of sophisticated thought. The “comatose” patients’ brain scans show that, in reply to questions by an examiner, the patients are in fact thinking and imagining.

The woman on the operating table who was talking to me while I removed her frontal lobe had both material and immaterial powers of mind. Our higher brain functions defy precise mapping onto brain tissue, because they are not generated by tissue, as our lower brain functions are.

Materialism, the view that matter is all that exists, is the premise of much contemporary thinking about what a human being is. Yet evidence from the laboratory, operating room, and clinical experience points to a less fashionable conclusion: Human beings straddle the material and immaterial realms.

We can do better science—and medicine—when we recognize that human beings have abilities that transcend reductionist material explanations. In this century of unprecedented advances in brain research, it’s remarkable that the deepest insights emerge from an ancient paradigm: Thomas Aquinas’s map of the soul.

Michael Egnor is a professor of neurological surgery at Stony Brook University School of Medicine.

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