part two: steps to a biology of mind

Fifteen years after President Bush senior inaugurated “The Decade of the Brain,” it is hard to believe that until fairly recently in human history, the idea that the brain is even involved in mental life was a matter of considerable dispute. Indeed, the first thinker on record to suggest a link between mind and brain was the Pythagorean Alcmaeon of Croton, writing in the fifth century BCE. Prior to that, across cultures, it was widely held that the mind, or soul, was located in the heart. The priests of ancient Egypt, for example, when preparing the body of the deceased for the afterlife, would pull out the brain, piece by piece through the nose, but would leave the heart intact, believing it to be the center of a person's being and intelligence. In most ancient cultures, the idea of dissecting a cadaver was taboo, so with no knowledge of the nervous system, it was only natural to conclude that the accelerated heartbeat that accompanied an excited mind was a clear indication of the bodily location of mental life. Even such great thinkers as Aristotle subscribed to this view. But, rigorous biologist that he was, Greece's greatest polymath was certain that the brain must serve some function. Noticing that it was cool to the touch, he concluded that it refrigerated the blood—a conclusion that also allowed him to account for the inordinately large brains of humans. Because of our unusual intelligence, he argued, our hearts produced more heat and, thus, required a larger cooling system.

Alcmaeon's brain-centered theory, however, did manage to persuade the likes of Hippocrates and Plato to abandon the prevailing “cardiovascular theory,” and despite Aristotle's resistance to the idea, it was picked up by physicians during the early Roman period who broke the taboo against dissecting cadavers and discovered the nervous system branching out from the skull and spine. Although this view gradually took hold, and has remained dominant ever since, it was still being disputed as late as the seventeenth century, when philosopher Henry More wrote, “This lax pith or marrow in man's head shows no more capacity for thought than a cake of suet or a bowl of curds.” It is also worth noting that the model of the brain that prevailed through most of the second millennium was very different from the model we subscribe to today. Whereas we now see a vast, complex electrochemical network of some hundred billion neurons, these early anatomists were convinced that the mind, or soul, was a kind of etheric presence that lived in large “ventricles” or chambers in the brain, communicating its commands to the rest of the body through “vital spirits” that flowed through the nervous system's minute pathways.

Indeed, it has been this move away from a spirit-based view of the brain's workings toward a purely biological one that has led to the idea, so unpopular with the religiously inclined, that the mind, or soul, is ultimately reducible to brain activity.

Like a hole in the head

The road to this now widely shared conviction has, like any scientific development, been marked by several major turning points. But few have struck the field with as much force as the story of a Vermont railroad worker named Phineas Gage. The year was 1848, and Gage was out supervising the construction of a section of track when an accidental explosion shot an iron rod more than three feet long and one and a quarter inches in diameter straight into his left cheek, through his frontal lobe and out through the top of his head, taking no small measure of brain with it. To everyone's amazement, Gage was back on his feet in a matter of minutes and appeared unfazed by the incident. In fact, according to the doctor who treated him an hour later, he was able to speak more lucidly about it than his shaken coworkers who had witnessed it. Although his basic cognitive functions remained unaltered, however, over time it became clear that something fundamental had changed. According to John Harlow, the physician who followed his case, where Gage had once been efficient, capable, and thoughtful, after the accident he became “fitful, irreverent, indulging at times in the grossest profanity, . . . manifesting but little deference for his fellows, impatient of restraint or advice when it conflicts with his desires.” So radical was the shift in personality that, “his friends and acquaintances said he was 'no longer Gage.'”

At the time of the Gage incident, there was already considerable speculation that specific regions of the brain were responsible for specific aspects of perception, cognition, and behavior—particularly among the “phrenologists,” who attempted to “map” the regions of the brain according to the lumps on the skull. But the reason Gage's case caused such a stir was that it seemed to suggest that there were even systems in the brain responsible for the creation of our personalities, our unique selves. In the century and a half since, studies of brain-damaged patients by clinical neurologists have revealed much about the relationship between the functioning of the brain and the way we experience and respond to the world. Their stories are often as perplexing as they are revealing.

In his book Phantoms in the Brain, neurologist V.S. Ramachandran tells the story of a young patient named Arthur who, after suffering a severe head injury in a car accident, began to insist that his parents were impostors. No matter how hard they tried to convince him otherwise, whenever he would see them, he would say, “You may look like my real parents, but I know you're not my real parents.” When they would call him on the phone, however, he immediately recognized them. This peculiar delusion, known as Capgras' syndrome, has been chronicled a number of times in psychiatric literature and has generally been given Freudian interpretations relating it to the notorious Oedipus complex. But Ramachandran had a different idea. His explanation was that a connection had been severed between one of the visual centers of the brain and one of the emotional centers. So despite the fact that Arthur could recognize his parents' faces, he didn't feel anything when he saw them. Though Arthur's father did manage to temporarily convince him of his authenticity (by apologizing for hiring the impostor parents), Arthur soon returned to his original delusion.

It is hard for most of us to imagine what it would be like to have one of our most taken-for-granted faculties suddenly no longer available to us, like the ability to respond emotionally to our visual experience. Indeed, what is most intriguing about these stories is the way in which they challenge one of our most fundamental intuitions—our sense that the self is a single, unified whole. Repeated throughout the neurology literature are cases in which damage to a specific part of the brain leads to the loss of some specific aspect of our ability to perceive and respond to the world. Damage one part of my brain and I'll lose the ability to learn any new facts. Damage another part and I'll be unable to recognize faces. Damage another area and my experience of the world will remain intact, but I'll be unable to find the words I need to speak clearly about it. Damage still another part and I'll lose the ability to pay attention to half of my visual field, but I will be convinced that the half I'm seeing is the whole picture. As a result, in the morning, I'll only shave half of my face. Taken together, the data from neurology suggest that despite our brain's ability to organize our experience of ourselves and the world into a seamless unity, we are, in fact, made up of many parts, the loss of any of which can have dramatic effects on the whole.

Being of two minds

When we think of brain damage, we generally think of damage caused by accident or disease. But there is also the kind of damage intentionally inflicted by surgeons in order to help resolve a brain disorder. Given our increased understanding of the delicate interrelatedness of the entire brain, such procedures are rarely done these days, owing in some part to the often disastrous results of the 45,000 frontal lobotomies performed in the U.S. in the 1940s and '50s. But another procedure, performed in the 1960s as a means to eliminate epileptic seizures, yielded some surprising findings for our understanding of the brain's relationship to the self.

However ignorant we may be of brain science, most of us are familiar by now with the idea that our brain has two hemispheres, a left one and a right one, each responsible for very different aspects of our behavior. Our dominant left brain, we are told, is more analytical; our right brain more emotional, creative, and intuitive. Although much of the popular psychology literature on the right brain–left brain distinction has been, in the eyes of neuroscience, exceedingly simplistic and inaccurate, the basic fact—known in the field as “hemispheric specialization”—is well established. In a normal brain, these two hemispheres communicate with one another through a large band of nervous tissue known as the corpus callosum (larger in women than in men, incidentally, accounting for their superior ability to multitask, among other things). But what would happen if the connection between these two halves of the brain was severed, leaving us, in effect, with two brains in our head? Would we end up with two different selves? Over the past few decades, a group of neuroscientists have had the chance to find out.

Epilepsy comes in many forms, some mild and some severe. In its worst manifestations, it brings with it nearly constant seizures that make life almost impossible for the patient. In an attempt to control these severe cases, in the 1960s neurosurgeons began cutting the corpus callosum to prevent the seizures from spreading from one side of the brain to the other. The procedure was remarkably successful, and to the relief of the doctors who pioneered the treatment, patients generally recovered well and were able to live relatively normal lives. But in these “split-brain” patients, psychobiologist Roger Sperry soon recognized a rare opportunity to study the differences between the two hemispheres in a way that had never been possible before. Over the decades that followed, he pioneered a series of studies that ultimately earned him a Nobel Prize. Most of these split-brain studies focused on illuminating the functional differences between the two hemispheres, but along the way, Sperry and his colleagues began to realize that there were implications to what they were seeing that went far beyond the scope of their initial questions.

One of the most commonly known facts about hemispheric specialization is that the right brain controls the left side of the body and the left brain controls the right side. Where visual input is concerned, the same rule applies. The left half of the visual field (of each eye) is routed to the right brain and vice versa. Knowing this, researchers realized that by presenting information quickly to only one side of the subject's visual field, they could ensure that the information only reached one side of the subject's brain. This technique provided the cornerstone of their research.

Employing this method, researchers had learned early on that the dominant left brain, with its ability to reason and use language, is the home of what we usually think of as the conscious mind. For instance, when asked to report on information that had been presented to their left brain alone, subjects could speak about it quite normally. When information had been presented only to the right brain, by contrast, subjects seemed unaware of it. As the research progressed, however, the picture grew more complex. For instance, when the right brain was shown an image of a spoon, the subject's left hand (which is controlled by the right brain) could successfully identify an actual spoon from among an assortment of objects, even though the subject claimed to have no conscious knowledge of having seen it. Despite its inability to express itself, the right brain nonetheless seemed to have a will and mind of its own. Eager to test this, Scottish neuroscientist Donald MacKay devised a twenty-questions-type guessing game and successfully taught each of the two halves of a patient's brain to play it—first against him and then against the other half. But this image of the two halves of one brain competing with one another soon moved from the experimental to the macabre, as split-brain patients began to develop the bizarre malady known as “alien-hand syndrome.”

Imagine just having zipped up your trousers with your dominant right hand only to find your left hand unzipping them and taking them off. Or reaching to embrace a lover only to find your left hand punching her in the face. Or attempting to shop at the supermarket as your left hand grabs unwanted items from the shelves and shoves them in your pocket. If this sounds like a story straight out of The Twilight Zone, it is nonetheless exactly what a number of split-brain patients began to report. One patient said it regularly took her half a day to pack for a trip because each time she put an item in her suitcase with her right hand, her left hand would remove it. Another said that he was even afraid to go to sleep for fear that his left hand would strangle him.

As extreme as it sounds that each half of a brain could have its own agenda, this fact was eventually demonstrated experimentally by neuroscientists Michael Gazzaniga and Joseph LeDoux. Although in most of us, the dominant left brain houses all of our language capacity, in a small percentage of the population, the right brain also develops some linguistic functions. Using a rare case of a young split-brain patient whose right brain had developed a slight capacity for printed language, the researchers asked both halves of the brain a series of questions, and found that, particularly where preferences and opinions were concerned, there was often disagreement. What was most revealing, though, was when the patient was asked about his ambitions. In response to the question: “What do you want to do when you graduate?” his dominant left hemisphere answered, vocally, “I want to be a draftsman. I'm already training for it.” His right hemisphere, which could only respond by using Scrabble letters to spell out its answer, responded “A-U-T-O-M-O-B-I-L-E R-A-C-E-[R].”

The idea that splitting the brain amounts to nothing less than splitting the self is a challenging one with enormous implications for our understanding of the brain's role in creating consciousness and even individuality. Therefore, it is no surprise that it has remained a controversial finding, even among scientists. But for the man who was awarded the Nobel Prize for his pioneering work in this area, the experience of working with split-brain patients for many years all pointed in one direction. “Everything we have seen indicates that the surgery has left these people with two separate minds,” Sperry wrote. “That is, two separate spheres of consciousness.”

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