I watched the CAT scan images appear on the screen, one by one. The baby’s head was mostly empty. There were only thin slivers of brain—a bit of brain tissue at the base of the skull, and a thin rim around the edges. The rest was water.
Her parents had feared this. We had seen it on the prenatal ultrasound; the CAT scan, hours after birth, was much more accurate. Katie looked like a normal newborn, but she had little chance at a normal life. She had a fraternal-twin sister in the incubator next to her. But Katie only had a third of the brain that her sister had. I explained all of this to her family, trying to keep alive a flicker of hope for their daughter.
I cared for Katie as she grew up. At every stage of Katie’s life so far, she has excelled. She sat and talked and walked earlier than her sister. She’s made the honor roll. She will soon graduate high school.
I’ve had other patients whose brains fell far short of their minds. Maria had only two-thirds of a brain. She needed a couple of operations to drain fluid, but she thrives. She just finished her master’s degree in English literature, and is a published musician. Jesse was born with a head shaped like a football and half-full of water – doctors told his mother to let him die at birth. She disobeyed. He is a normal happy middle-schooler, loves sports, and wears his hair long.
Some people with deficient brains are profoundly handicapped. But not all are. I’ve treated and cared for scores of kids who grow up with brains that are deficient but minds that thrive. How is this possible? Neuroscience, and Thomas Aquinas, point to the answer.
Is the Mind Mechanical?
As a medical student, I fell in love with the brain. It’s a daunting organ: an ensemble of cells and axons and nuclei and lobes tucked and folded in exotic shapes. I had to learn what it looks like when it’s sliced through by CAT scans, and then what it looks like when I slice through it. My fascination with neuroanatomy was metaphysical: this was where our thoughts and decisions came from, this was a roadmap of the human self, and I was learning to read it as I read a book. It was the truth about us, I thought.
But I was wrong. Katie made me face my misunderstanding. She was a whole person. The child in my office was not mapped in any meaningful way to the scan of her brain or the diagram in my neuroanatomy textbook. The roadmap got it wrong.
How does the mind relate to the brain? This question is central to my professional life. I thought I had it answered. Yet a century of research and 30 years of my own neurosurgical practice have challenged everything I thought I knew.
The view assumed by those who taught me is that the mind is wholly a product of the brain, which is itself understood as something like a machine. Francis Crick, a neuroscientist and the Nobel laureate who was the co-discoverer of the structure of DNA, wrote that “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 influence them.”
This mechanical philosophy is the result of two steps. It began with Rene Descartes, who argued that the mind and the brain were separate substances, immaterial and material. Somehow (how, neither Descartes nor anyone else can say) the mind is linked to the brain— it’s the ghost in the machine.
But as Francis Bacon’s approach to understanding the world gained ascendency during the scientific Enlightenment, it became fashionable to limit inquiry about the world to physical substances: to study the machine and ignore the ghost. Matter was tractable, and we studied it to obsession. The ghost was ignored, and then denied. This was what the logic of materialism demanded.
The materialist insists that we are slaves of our neurons, without genuine free will. Materialism comes in different flavors, each having passed into and then out of favor over the past century, as their insufficiency became apparent. Behaviorists asserted that the mind, if it exists at all, is irrelevant. All that matters is what is observable—input and output. Yet behaviorism is in eclipse, because it’s difficult to deny the relevance of the mind to neuroscience.
Identity theory, replacing behaviorism, held that the mind just is the brain. Thoughts and sensations are exactly the same thing as brain tissue and neurotransmitters, understood differently. The pain you feel in your finger is identical to the nerve impulses in your arm and in your brain. But, of course, that’s not really true. Pain hurts and nerve impulses are electrical and chemical. They’re not even similar. Identity theorists struggled with uncooperative reality for a generation, then gave up.
Computer functionalism came next: the brain is hardware and mind is software. But this too has problems. Nineteenth-century German philosopher Franz Brentano pointed out that the one thing that absolutely distinguishes thoughts from matter is that thoughts are always about something, and matter is never about anything. This aboutness is the hallmark of the mind. Every thought has a meaning. No material thing has meaning.
Computation is the mapping of an input to an output according to an algorithm, irrespective of meaning. Computation has no aboutness; it is the antithesis of thought.
Neuroscience and Metaphysics
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.
One of the neurosurgeons who pioneered the corpus callosotomy for epilepsy patients was Wilder Penfield, who worked in Montreal in the middle of the twentieth century. Penfield studied the brains and minds of epileptic patients in a remarkably direct way, in the course of treating them. He operated on people who were awake. The brain itself feels no pain, and local anesthetics numb the scalp and skull enough to permit painless brain surgery. Penfield asked them to do and think things while he was observing and temporarily stimulating or impairing regions of their brains. Two things astonished him.