Professor of Neuroscience and Novelist, Princeton University:
In my last post I commented about the link between the brain and the mind. That post received so much interest and so many comments from all perspectives that I thought it would be useful to explore the topic more systematically. Nobody should be mistaken about the cultural importance of the topic. The link between the mind and the brain is not merely a medical story. Its implications reach into almost all aspects of religion and spirituality including the belief in God, ghosts, angels, devils, and life after death.
When most of us think about the key conflicts between science and religion, we tend to think about Darwin's theory of evolution published in 1859, or Galileo's persecution by the Catholic Church in the 17th century. These famous clashes between science and religion are resolvable. Every sensible modern religion accepts the fact that the Earth orbits the Sun. Liberal religions are gradually accepting the scientific fact of biological evolution.
One disconnect between religion and science, however, is much older, much more profound, and may be much harder to bridge. It dates back at least to Hippocrates in the fifth century BC. At that time there was no formal science as it is recognized today. Hippocrates was nonetheless an acute medical observer and noticed that people with brain damage tended to lose some of their mental abilities. A passage attributed to him summarizes his view elegantly:
"Men ought to know that from the brain, and from the brain only, arise our pleasures, joys, laughter and jests, as well as our sorrows, pains, griefs and tears. Through it, in particular, we think, see, hear, and distinguish the ugly from the beautiful, the bad from the good, the pleasant from the unpleasant..."
Hippocrates evidently understood the central conflict between observation and most spiritual beliefs. The belief in a spirit world, a world of consciousness that exists independently of physical substance, that survives the death of the body, that comprises ghosts and angels and deities, is incompatible with the observation that damage to the physical brain systematically takes away chunks of the mind. The medical facts suggest that mind, though it definitely exists, is something created by the brain and that it dies piece-by-piece as the brain dies.
About a century later Aristotle famously disagreed with Hippocrates, placing the mind in the human heart. Aristotle listed his reasons, many of which sound vaguely plausible given the analogical and somewhat mystical thinking of the time. How did Aristotle go so wrong in his medical analysis? He was a theoretician. Hippocrates, who worked in a hospital, saw the effects of brain damage every day and grounded his theory in observation. Nobody who spends appreciable time with brain-damaged patients can avoid the obvious conclusion. The brain is the source of the mind.
Another famous view of the brain/mind problem was outlined by Descartes two thousand years later, in the 17th century. In Descartes' view the mind was an ethereal substance, a fluid, that was stored in a receptacle in the brain. When he dissected the human brain he noticed that almost every structure came in pairs, one on each side. The human soul was obviously a single entity and therefore it could not be stored in a double structure. In the end he found a small single object at the center of the brain, the pineal body, and deduced that it was the house of the soul. The pineal body is now known to be a gland that produces melatonin and has nothing whatever to do with a soul.
Descartes' idea, aside from being wrong in the particulars, has a deeper problem. There is no part of the brain that, when damaged, takes away the Cartesian soul. Instead damage to different structures takes away different chunks of the mind. The ability to formulate a sentence? Lost in damage to Broca's area. The ability to understand language? Lost in damage to Wernicke's area. The ability to see, imagine, or comprehend color? Lost in damage to specific regions of the visual system. The ability to think about the space around the body? Lost in damage to another set of brain areas. The ability to intuit the feelings and intentions of others? Impaired after a stroke to a specific network of brain regions. And so on. The mind is a collective and bits of it die when parts of the machinery are mucked up. Even awareness itself, as I wrote about last time, can be splintered apart and compromised by brain damage.
The effect of brain damage is certainly not the only pertinent evidence. Some of the more interesting evidence comes from the direct electrical stimulation of the brain. A little more than a century ago scientists tried applying minute sparks of electricity to surface of the brain, stimulating the circuitry. The technique was improved and elaborated and is now one of the main methods for probing the brain's circuitry. For example, before removing a tumor from a person's brain, a surgeon will expose the brain while the person is awake and under local anesthetic. The surgeon will then study the effect of electrical stimulation, mapping out the function of this and that brain area, to avoid surgically removing any area necessary for language. Some of the most colorful and memorable experiments of this type were done by Penfield in the early 20th century. He found, as have many others since, that electrically tickling a specific spot in the circuitry has a specific and predictable effect on the mind. Whether seeing, hearing, feeling hunger, feeling rage, remembering a scene from childhood, making a coordinated gesture, even feeling as though you've intentionally chosen to make the gesture, these many bits and components of mind can be turned on and off by altering the activity of neurons.
The evidence is now overwhelming that every aspect of the mind is produced by the brain.
The realization that the brain produces the mind is similar in some ways to the theory of evolution before Charles Darwin got to it. Prior to Darwin, the theory of evolution was much discussed and the fossil record certainly supported it, but nobody could point to a plausible mechanism. How exactly did one species evolve over time into many new species? Darwin proposed a mechanism that fit the evidence: natural selection. Survival of the fittest. With the discovery of this simple mechanism, the science of biology was revolutionized.
The idea that the mind depends on the action of the brain is amply supported by the scientific evidence. But nobody knows how a brain produces the inner experience -- the feeling of consciousness. What is the mechanism? That is the question of our time. Many theories have been proposed, including one of my own, and only time and data will tell who is right.
I draw two personal lessons from the neuroscience of mind.
First, far from dismissing mind, or spirit, or soul as nonsense, I see these quantities as far more precious precisely because they are vulnerable and finite. In a sense I've become more spiritual as my scientific understanding deepens and I realize that spirit is a passing conjunction of information.
Second, the neuroscience of the mind gives me a wonderful opportunity to work on a scientific problem that is truly meaningful. About 25 years ago Francis Crick, famous for his role in understanding DNA, posed a question. Is it possible for brain science to address consciousness, a topic traditionally studied by philosophers and theologians? The answer is a definite yes. Many neuroscientists including myself have joined that effort.