May 6, 2010
Nothing; not science, not theology, not politics, not love: Nothing means anything without our brains. Everything we know and do, all the sense of human thought, all the feelings of human emotion, all the questions of human existence—all are the product of the brains in our heads.
Thought, emotion, existence—I’ve yearned to know what it’s all about. One could start with physics, philosophy, psychology, religion. I start with the human brain. How do human brains think and feel?
Rodolfo Llinas, the chair of physiology and neuroscience at New York University Medical Center, has wondered about the brain his entire life. “Of all our organs, the brain is the most spectacular,” he says. “At about three pounds, it’s 2 percent of the body’s weight, yet requires 25 percent of the body’s energy.”
How did this come to be? What do we need brains for? What is it that they do that makes them so special?
Llinas has a particular view, which some might call idiosyncratic. “The brain evolved to be able to move in an intelligent fashion,” he says. “First of all, if you’re going to move, it’s going to cost you an enormous amount of energy. This means you have to be able to eat other animals because you cannot get enough energy from the sun. You also have to flee from other animals trying to eat you. Hence, you require joints and muscles and so on, but you also need to have a desire to move, you need intentionality.”
He continues: “In order to have intentionality, you need the ability to predict. You don’t want to move into danger. So I consider these three basic things to be what brains are about—movement, intentionality, and prediction.“
What then, I ask, is thinking?
“Thinking is a pre-motor event,” Llinas states. “Thinking is internalized movement. Thinking is all the things that you could do, out of which you will choose those things you will do. We are emulating reality inside our head. We have managed to generate a dreamlike condition where we actually have sounds and objects that move with respect to backgrounds and all of these things without effort. So that is basically what the nervous system is for. It’s a huge, beautiful device to emulate reality.”
Movement, intentionality, predicting. According to Llinas, that’s what the brain does. All else is derived from these, he says. All the expressions of human personality, all the flourishings of human civilization, come from movement, intentionality, predicting.
But how does the brain do it?
To begin to find out, we can now look inside a living brain.
John Mazziotta, director of UCLA’s Brain Mapping Center, says that the new imaging tools can unlock mysteries of emotions, decision making, social cognition, and how people interact with one another. “If you’re exposed to something that you find enjoyable—it could be food, art, a political message; it doesn’t matter, if it’s a match with what you like—you have certain networks in the brain that become active,” he says. “Alternatively, if the stimulus is something you do not like, other networks are involved.”
Mazziotta explains that even the same stimulus in the same person can have different effects. “If you feed people foods that they enjoy, one brain system is active,” he explains, “but if you make them eat the same food excessively until they are revolted by it, another brain system becomes active.”
What about emotion? Joy, excitement, anger, fear? How does the brain add feelings?
Joseph LeDoux, a professor in New York University’s Center for Neural Science, is an expert on the amygdala, the almond-shaped nucleus deep within the brain that is involved in feelings of fear—the “fight or flight” response.
“The thing to understand about the amygdala is that the reason it does what it does is simply because of its wiring,” LeDoux says. “There’s no mysticism about it at all. It receives inputs from the external world, from all the senses, and then it connects up to responses that control our bodily physiology—blood pressure, heart rate, sweating, hormone secretions, all of the physiological signs that reflect aroused emotion. The central nucleus of the amygdala connects to the hypothalamus and the brain stem and controls all of those responses.”
This “innate wiring was put into the brain by evolution,” LeDoux says. “That’s why rats are naturally afraid of cats, and why we have innate fears of snakes and spiders—because they were dangerous to our ancestors.”
How important are affective or emotional behaviors in terms of the totality of sentient life?
LeDoux says that “affective emotional behaviors are essential to our entire being. We don’t do anything that’s not affective in one way or another. Those are the things that move us. If we want to understand what it is to be human, we must understand our emotions.”
So it seems that what feels “so me”—my feelings—is not “so me.” Emotions are a mechanism, localized in the brain, generated by the brain. Emotions are not mysteries: They are observable inside the brain; they are testable and can be manipulated.
But the brain is not like a computer, hardwired and fixed forever. The brain can change. Even with a doctorate in brain research (admittedly four decades ancient), I’m shocked by how much plasticity is the basis of higher brain function.
Brain scientist Michael Merzenich has pioneered cochlear implants, enabling people who become profoundly deaf to hear again. But how could such crude devices work so wonderfully? The brain would have to give up a deep secret.
“One of the most exciting things that’s happened in neuroscience is that we now have this completely different view of how the brain is operating,” Merzenich says. “We now realize that the brain is actually remodeling itself, revising itself massively as we evolve in our abilities. The brain has a wonderful trick. It simply strengthens all of the connections that contribute to a better try.”
He gives an example. “Let’s say I’m bouncing a ping pong ball on a paddle, and initially I get only one or two bounces right. But my brain knows what success is. It has a model of success. It’s probably seen my brother or somebody do it successfully. And when it sees success, it rewards itself. And it rewards itself by releasing neural transmitters that basically tell the brain, ‘Hey, save those connections. That was a good one.’ And through a series of successive approximations, it saves those changes that result in better and better performances. Ultimately, I master it.”
He stresses: “It’s a wonderful trick to control your own brain plasticity, to control your own evolution.”
Merzenich tells the remarkable story of the cochlear implant, which, in my sense of things, is one of the most powerful probative discoveries of how the brain really works. Placed in the inner ear, a cochlear implant, he explains, “is designed to deliver shocks to the auditory nerve in response to sound, to deliver input into the brain that can simulate the input that’s normally delivered by sound, so that now oral speech can be understood by the person again, so the deaf can recover their speech and language.”
What is amazing is that compared with the natural auditory nerve, these electrical stimulating devises are extremely crude. Merzenich says the devices are “necessarily very crude,” whereas the normal input via the auditory nerve is “very sophisticated.” For a long time, he explains, “scientists imagined that all of those details of the individual neurons [nerve cells] really mattered. Now, we enable sounds to be understood as language with a crude device that shocks the auditory nerve grossly. It’s a little bit akin to playing Chopin with your forearms!”
But eventually it works! “These patients can talk to you on the phone,” Merzenich says. But how does it work?
He gives the sequence of events: “At first, when the device is turned on and I speak to my patients, they say what they hear sounds like crap, it sounds like noise, it sounds like a language they have never heard before. But then a few months later, perhaps four to eight months, they hear and understand everything. How? It’s not a product of better or marvelous engineering—the device is the same. The dramatically improved results can only be attributed to the incredible power of the brain to adapt, to create a new construct of the cacophony of crude sounds that convey the language, a construct that’s just as useful as the old one.”
How on earth can these deaf people grow to have a unified, simple understanding with so little real information? “The only way you can account for it is if the brain reconstructs a new language representation from this very crude, inner-ear new information,” Merzenich says. “Therefore, I’ve come to deeply appreciate how the brain organizes activity, an incredibly powerful top-down process that uses its stored information [memories] to take this new aural trash [i.e., the crude shocks to the auditory nerve] and turn it into language gold—and then to connect it seamlessly to all information in the brain.”
Merzenich continues: “Aural information coming to them in a very different form, encoded in a radically different way—a coarse and crude way—comes to seem ‘perfectly natural.’ This is astonishing, and it is decisively and decidedly a trick of the brain. It’s something I could have never predicted.”
Playing Chopin—say the etudes—with your forearms! A perfect analogy. Plasticity adapts the brain to its environment, even repairs brain damage.
Remarkable, yes—but this I could always accept. To restructure the rough, rudimentary nonsense of artificial electrical impulses into the exquisitely fine structure of intelligible sounds astounds me. After a lifetime following brain research, I’m flabbergasted!
What other mysteries does the brain hold? Brain hemispheres are vital for cognition. What about right and left brains? How do they differ?
Split-brain researcher Eran Zaidel speculates that for important computations, “one side will compute, while the other side will monitor or compute in another way. So, one way to describe the division of labor between the two sides is to say that one side is ‘top down’ and one side is ‘bottom up.’ When we perceive the forest, do we see the trees first and then those trees make up a forest? Or do we see the forest first, and then we see the trees? It turns out we do both.” And creativity, Zaidel says, is “a function of the connection between the two.”
Zaidel notes that the standard view—that (in right-handed people) the left side of the brain is specialized for language while the right side is specialized for space and attention—is “generally true, but it doesn’t capture everything. One can also talk about the perceptual style of the two sides: the left hemisphere being analytic and the right hemisphere synthetic. Discerning a detail in a more complex design is what the left hemisphere is good at. On the other hand, the ability to complete a figure that’s incomplete, to see things from unusual perspectives, is right-hemispheric. When there is brain damage to the left side, people suffer major problems in language. Right-side damage causes problems with space and attention.”
Split-brain patients fascinate by providing a special window into inner consciousness. (These are generally patients with intractable epilepsy whose connections between left and right brain hemispheres must be severed in order for them to regain some semblance of normal life.) They shatter our apparently sure sense of a unity of consciousness by behaving as if they know things that they vow they do not know.
A typical patient, Zaidel says, would not appear unusual. “In fact, if you see a split-brain person walking on the street, you wouldn’t tell them apart from any other person, which is amazing because the largest fiber system in the brain—200 million nerve fibers—has been cut and nothing seems to happen.”
But when you test them in a laboratory, he continues, “you discover that split-brain patients have many unusual characteristics. Basically, you find two different people in the same brain. It’s unbelievable. We have two separate sensory systems; two separate perceptual apparatuses; two separate memory systems, languages, personalities, consciousnesses. You can ask each brain hemisphere questions about itself and you get two different views. This suggests that consciousness is not necessarily unified in the sense that it can have different representations at different times, even in the same brain.”
One consequence of this discovery, Zaidel says, is that “it introduces problems for religious people who believe in the unity of the will, of the self, and of the soul.”
One disorder that is very dramatic is called “hemineglect.” Zaidel explains that when there is damage to the right parietal brain, patients who may be very intelligent and verbal simply ignore the left half of their visual space. If the damage is large enough, the patient may have, say, a paralyzed left hand, but he denies his illness (a condition that is called “anosognosia”). The patient doesn’t know that he has a deficit, so this is a disorder of consciousness. “He denies that this paralyzed hand is his own hand,” Zaidel explains. “He may give it a name, ‘Charlie.’ ‘What do you mean, Charlie?’ ‘It’s a hand,’ the patient says. As a researcher, I may respond: ‘Whose hand is it? Yours? Mine? It’s connected to your body.’ ‘I know,’ the patient says, ‘but it has a will of its own.’”
Another example of anosognosia, Zaidel relates, is when “you show these brain-damaged patients two identical pictures of a house, except that the one on the bottom has some flames coming out of its left half. ‘What do you see on top?’ I ask. ‘A house,’ he says. ‘What do you see on bottom?’ ‘A house.’ ‘What’s the difference between the two houses?’ ‘None.’ ‘Are they identical?’ ‘Yes.’ ‘Where would you rather live?’ ‘The top one.’ ‘Why?’ ‘I don’t know; it just feels better.’”
Here is a case, Zaidel concludes, where the patient does process the information in the neglected field, but he doesn’t know that he does. Meaningful semantic information is being processed—i.e., fire is bad—but it is not penetrating consciousness.
How to sum up? How does the human brain think and feel? How does it happen that three pounds of meat understands science, appreciates art, experiences love?
Here are some categories by which to understand the brain.
Specific brain structures: wired for specialized purposes, like the amygdala for fear.
Specialized brain functions: change over time, through learning.
Brain networks: waxing and waning, always dynamic.
Brain plasticity: the brain always reinventing itself.
Dual cerebral hemispheres: left and right, with complex computational relationships.
What, then, is human consciousness?
Of only this, be sure: Understanding the brain gets us closer to truth.
Robert Lawrence Kuhn speaks with Rodolfo Llinas, John Mazziotta, Joseph LeDoux, Michael Merzenich, and Eran Zaidel in “How Do Human Brains Think and Feel?”—the 14th episode in the new season of the Closer To Truth: Cosmos, Consciousness, God TV series (53rd in total).
The series airs on PBS World (often Thursdays, twice) and many other PBS and noncommercial stations. Every Thursday, participants will discuss the current episode.
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