Have you heard of Phineas Gage? He was a railroad worker who, in 1848, was tamping down black powder with an iron rod when the powder blew up and shot the rod through his head, coming in under his left cheekbone and out the top. This picture shows him with the rod, his “constant companion.” (To see his skull and a recreation of where the rod went, go here.)
Mind/brain connection
So what happens when much of the left frontal lobe of a person’s brain is destroyed? His case was one of the first examples that modern medicine had to see how cognition and personality—what we think of as the mind—are connected to the physical brain. Accounts differ as to how severe and how prolonged Gage’s personality change was, but it does seem to have been substantial, at least temporarily.
Modern science has continued to find the connection between various parts of the brain and different functions so that the mind is often defined as simply what the brain does. For example, Henry Molaison had part of his brain surgically removed in 1953 to treat epilepsy. An unintended consequence of the surgery was a type of amnesia in which he could remember (with some loss) events before the operation, but he couldn’t form new memories. He could update old memories and he could learn new motor skills, but he couldn’t remember learning them. He was studied by scientists until his death in 2008.
Another example is Clive Wearing, a British musicologist who got amnesia because of encephalitis in 1985. His long term memory is poor, and he can’t remember new events for more than 30 seconds. He feels like he is continually waking up. He can still play the piano, though he has no recollection of ever being taught.
Then there’s Klüver-Bucy Syndrome, the rare result of some kinds of brain damage from surgery or disease. Its symptoms include hypersexuality, even in children. Or aphasia, the loss of the ability to speak, which usually comes from strokes. Or the kinds of personality and memory loss caused by Alzheimer’s and other kinds of dementia. Or even prions, the misshapen proteins that cause BSE (“mad cow disease”) in cattle and similar degenerative brain diseases in humans and are thought to be transmitted through food.
The more unusual of these are the fascinating kinds of stories that neurologist Oliver Sacks writes about in The Man Who Mistook His Wife for a Hat and other popular books. Indeed, Sacks himself has an interesting disorder, prosopamnesia, the inability to recognize faces.
The “mind” is a useful idea, but this close connection between the brain and mental function leaves no room for the mind—as something separate from the brain—to hide. The same is true for the soul. As a term for someone’s essence or moral character, it’s a useful word, but there is no evidence that the soul exists as anything more than an abstract concept.
The brain behaves exactly as if it’s all that there is, not that it is simply the shoebox in which the soul is stored. How could an injury to the shoebox affect its contents, when the soul is immutable and will be good as new in heaven?
What does physics say?
Physics isn’t a field that usually has much to say about the soul, but a video by physicist Sean Carroll of CalTech makes the intriguing argument that physics shows not only that souls don’t exist but that nothing supernatural exists.
There’s plenty of physics that we don’t yet understand, he says, but the physics of our Newtonian world is all understood. For example, you don’t need to understand string theory to work in chemistry. Any physics that operates in our world would be known to us by now, which leaves no room for the supernatural.

Could new particles hide from our view? Sure, but only if they were (1) very weakly interacting or (2) too heavy to create or (3) too short-lived to detect. In any of those cases, the new particle would be irrelevant to our everyday lives. (@ 4:20)

Everyday physics is understood. We are done. It’s nothing more than

electrons and quarks, with mass from the Higgs field, interacting via gravity, electromagnetism, and the nuclear forces. That’s the everyday world. (@ 6:15)

The physics that remains are non-everyday physics (dark matter, dark energy, quantum gravity, origin of the universe, etc.) and complicated systems that are the result of the understood physics (superconductivity, turbulence, cancer, consciousness, etc.).
Compare physics with chess. Knowing the rules of chess doesn’t make you a grandmaster, but it does constrain the kinds of games you can play. Any games in which the pawn moves like a queen, for example, can be simply ruled out.
In physics, we know the rules of the everyday world, and this constrains the kinds of things that make sense. We know enough to simply rule out astrology, claims of clairvoyance, ESP, life after death, homeopathy, and other supernatural claims. If these claims were true, we would know that already.

If you believe in life after death, tell me what particles contain the information that moves your soul from place to place. (@ 9:30)

The ideas that the soul actually exists and that the mind is separate from the brain belong back to the time when demons were said to cause mental illness.

What is freedom of expression?
Without the freedom to offend,
it ceases to exist.
— Salman Rushdie

Photo credit: Wikipedia