Incognito (20 page)

For the purpose of illustrating the team-of-rivals framework, I have made the oversimplification of subdividing the neuroanatomy into the rational and emotional systems. But I do not want to give the impression that these are the only competing factions. Instead, they are only the beginning of the team-of-rivals story. Everywhere we look we find overlapping systems that compete.

One of the most fascinating examples of competing systems can be seen with the two
hemispheres of the brain, left and right. The hemispheres look roughly alike and are connected by a dense highway of fibers called the corpus callosum. No one would have guessed that the left and right hemispheres formed two halves of a team of rivals until the 1950s, when an unusual set of surgeries were undertaken. Neurobiologists
Roger Sperry and
Ronald Meyers, in some experimental surgeries, cut the corpus callosum of cats and monkeys. What happened? Not much. The animals acted normal, as though the massive band of fibers connecting the two halves was not really necessary.

As a result of this success, split-brain surgery was first performed on human epilepsy patients in 1961. For them, an operation that prevented the spread of seizures from one hemisphere to the other was the last hope. And the surgeries worked beautifully. A person who had suffered terribly with debilitating seizures could now live a normal life. Even with the two halves of his brain separated, the patient did not seem to act differently. He could remember events normally and learn new facts without trouble. He could love and laugh and dance and have fun.

But something strange was going on. If clever strategies were used to deliver information only to one hemisphere and not the other, then one hemisphere could learn something while the other would not. It was as though the person had two independent brains.
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And the patients could do different tasks at the same time, something that normal brains cannot do. For example, with a pencil in each hand, split brain patients could simultaneously draw incompatible figures, such as a circle and a triangle.

There was more. The main motor wiring of the brain crosses sides, such that the right hemisphere controls the left hand and the left hemisphere controls the right hand. And that fact allows a remarkable demonstration. Imagine that the word
apple
is flashed to the left hemisphere, while the word
pencil
is simultaneously flashed to the right hemisphere. When a split-brain patient is asked to grab the item he just saw, the right hand will pick up the apple while the left hand will simultaneously pick up the pencil. The two halves are now living their own lives, disconnected.

Researchers came to realize, over time, that the two hemispheres have somewhat different personalities and skills—this includes their abilities to think abstractly, create stories, draw inferences, determine the source of a memory, and make good choices in a gambling game. Roger Sperry, one of the neurobiologists who pioneered the split-brain studies (and garnered a Nobel Prize for it), came to understand the brain as “two separate realms of conscious awareness; two sensing, perceiving, thinking and remembering systems.” The two halves constitute a team of rivals: agents with the same goals but slightly different ways of going about it.

In 1976, the American psychologist
Julian Jaynes proposed that until late in the second millennium B.C.E., humans had no introspective consciousness, and that instead their minds were essentially divided into two, with their left hemispheres following the commands from their right hemispheres.
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These commands, in the form of auditory hallucinations, were interpreted as voices from the gods. About three thousand years ago, Jaynes suggests, this division of labor between the left and right hemispheres began to
break down. As the hemispheres began to communicate more smoothly, cognitive processes such as introspection were able to develop. The origin of consciousness, he argues, resulted from the ability of the two hemispheres to sit down at the table together and work out their differences. No one yet knows whether Jaynes’s theory has legs, but the proposal is too interesting to ignore.

The two hemispheres look almost identical anatomically. It’s as though you come equipped with the same basic model of brain hemisphere in the two sides of your skull, both absorbing data from the world in slightly different ways. It’s essentially one blueprint stamped out twice. And nothing could be better suited for a team of rivals. The fact that the two halves are doubles of the same basic plan is evidenced by a type of surgery called a hemispherectomy, in which one entire half of the brain is removed (this is done to treat intractable epilepsy caused by Rasmussen’s encephalitis). Amazingly, as long as the surgery is performed on a child before he is about eight years old, the child is fine. Let me repeat that: the child, with only half his brain remaining, is fine. He can eat, read, speak, do math, make friends, play chess, love his parents, and everything else that a child with two hemispheres can do. Note that it is not possible to remove
any
half of the brain: you cannot remove the front half or the back half and expect survival. But the right and left halves reveal themselves as something like copies of each other. Take one away and you still have another, with roughly redundant function. Just like a pair of political parties. If the Republicans or Democrats disappeared, the other would still be able to run the country. The approach would be slightly different, but things would still work.

I’ve begun with examples of rational systems versus emotional systems, and the two-factions-in-one-brain phenomenon
unmasked by split-brain surgeries. But the rivalries in the brain are far more numerous, and far more subtle, than the broad-stroke ones I have introduced so far. The brain is full of smaller subsystems that have overlapping domains and take care of coinciding tasks.

Consider
memory. Nature seems to have invented mechanisms for storing memory more than once. For instance, under normal circumstances, your memories of daily events are consolidated (that is, “cemented in”) by an area of the brain called the
hippocampus. But during frightening situations—such as a car accident or a robbery—another area, the
amygdala, also lays down memories along an independent, secondary memory track.
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Amygdala memories have a different quality to them: they are difficult to erase and they can pop back up in “flashbulb” fashion—as commonly described by rape victims and war veterans. In other words, there is more than one way to lay down memory. We’re not talking about a memory of different events, but multiple memories of the
same
event—as though two journalists with different personalities were jotting down notes about a single unfolding story.

So we see that different factions in the brain can get involved in the same task. In the end, it is likely that there are even more than two factions involved, all writing down information and later competing to tell the story.
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The conviction that memory is one thing is an illusion.

Here’s another example of overlapping domains. Scientists have long debated how the brain detects
motion. There are many theoretical ways to build motion detectors out of neurons, and the scientific literature has proposed wildly different models that involve connections between neurons, or the extended processes of neurons (called dendrites), or large populations of neurons.
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The details aren’t important here; what’s important is that these different theories have kindled decades of debates among academics. Because the proposed models are too small to measure directly, researchers design clever experiments to support or contradict various theories. The interesting outcome has been that most of the experiments are inconclusive,
supporting one model over another in some laboratory conditions but not in others. This has led to a growing recognition (reluctantly, for some) that there are
many
ways the visual system detects motion. Different strategies are implemented in different places in the brain. As with memory, the lesson here is that the brain has evolved multiple, redundant ways of solving problems.
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The neural factions often agree about what is out there in the world, but not always. And this provides the perfect substrate for a neural democracy.

The point I want to emphasize is that biology rarely rests with a single solution. Instead, it tends to ceaselessly reinvent solutions. But why endlessly innovate—why not find a good solution and move on? Unlike the artificial intelligence laboratory, the laboratory of nature has no master programmer who checks off a subroutine once it is invented. Once the
stack block
program is coded and polished, human programmers move on to the next important step. I propose that this moving on is a major reason artificial intelligence has become stuck. Biology, in contrast to artificial intelligence, takes a different approach: when a biological circuit for
detect motion
has been stumbled upon, there is no master programmer to report this to, and so random mutation continues to ceaselessly invent new variations in circuitry, solving
detect motion
in unexpected and creative new ways.

This viewpoint suggests a new approach to thinking about the brain. Most of the neuroscience literature seeks
the
solution to whatever brain function is being studied. But that approach may be misguided. If a space alien landed on Earth and discovered an animal that could climb a tree (say, a monkey), it would be rash for the alien to conclude that the monkey is the only animal with these skills. If the alien keeps looking, it will quickly discover that ants, squirrels, and jaguars also climb trees. And this is how it goes with clever mechanisms in biology: when we keep looking, we find more. Biology never checks off a problem and calls it quits. It reinvents solutions continually. The end product of that approach is a highly overlapping system of solutions—the necessary condition for a team-of-rivals architecture.
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The members of a team can often disagree, but they do not have to. In fact, much of the time rivals enjoy a natural concordance. And that simple fact allows a team of rivals to be robust in the face of losing parts of the system. Let’s return to the thought experiment of a disappearing political party. Imagine that all the key decision makers of a particular party were to die in an airplane crash, and let’s consider this roughly analogous to brain damage. In many cases the loss of one party would expose the polarized, opposing opinions of a rival group—as in the case when the frontal lobes are damaged, allowing for bad behavior such as shoplifting or urinating in public. But there are other cases, perhaps much more common, in which the disappearance of a political party goes unnoticed, because all the other parties hold roughly the same opinion on some matter (for example, the importance of funding residential trash collection). This is the hallmark of a robust biological system: political parties can perish in a tragic accident and the society will still run, sometimes with little more than a hiccup to the system. It may be that for every strange clinical case in which brain damage leads to a bizarre change in behavior or perception, there are hundreds of cases in which parts of the brain are damaged with no detectable clinical sign.

An advantage of
overlapping domains can be seen in the newly discovered phenomenon of
cognitive reserve
. Many people are found to have the neural ravages of
Alzheimer’s disease upon autopsy—but they never showed the symptoms while they were alive. How can this be? It turns out that these people continued to challenge their brains into old age by staying active in their careers, doing crossword puzzles, or carrying out any other activities that kept their neural populations well exercised. As a result of staying mentally vigorous, they built what neuropsychologists call cognitive reserve. It’s not that cognitively fit people don’t get
Alzheimer’s; it’s that their brains have protection against the symptoms. Even while parts of their brains degrade, they have other ways of solving problems. They are not stuck in the rut of having a single solution; instead, thanks to a lifetime of seeking out and building up redundant strategies, they have alternative solutions. When parts of the neural population degraded away, they were not even missed.

Cognitive reserve—and robustness in general—is achieved by blanketing a problem with overlapping solutions. As an analogy, consider a handyman. If he has several tools in his toolbox, then losing his hammer does not end his career. He can use his crowbar or the flat side of his pipe wrench. The handyman with only a couple of tools is in worse trouble.

The secret of redundancy allows us to understand what was previously a bizarre clinical mystery. Imagine that a patient sustains damage to a large chunk of her primary visual cortex, and an entire half of her visual field is now blind. You, the experimenter, pick up a cardboard shape, hold it up to her blind side, and ask her, “What do you see here?”

She says, “I have no idea—I’m blind in that half of my visual field.”

“I know,” you say. “But take a guess. Do you see a circle, square, or triangle?”

She says, “I really can’t tell you. I don’t see anything at all. I’m blind there.”

You say, “I know, I know. But
guess
.”

Finally, with exasperation, she guesses that the shape is a triangle. And she’s
correct
, well above what random chance would predict.
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Even though she’s blind, she can tease out a hunch—and this indicates that
something
in her brain is seeing. It’s just not the conscious part that depends on the integrity of her visual cortex. This phenomenon is called
blindsight, and it teaches us that when conscious vision is lost, there are still subcortical factory workers behind the scenes running their normal programs. So removal of parts of the brain (in this case, the cortex) reveals underlying structures that
do the same thing, just not as well. And from a neuroanatomical point of view, this is not surprising: after all, reptiles can see even though they have no cortex at all. They don’t see as well as we do, but they see.
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