The Left Brain Speaks, the Right Brain Laughs Read online

  In everything we do, there’s a hierarchy of perspective, from immediate to barely tangible to fully abstract. To understand how we react to challenges, it helps to start with something easy, like the imminent attack of a saber-toothed tiger.

  But first, a few words about what makes you so damn smart (and good lookin’).

  2.2 EVOLUTION

  Natural selection is a more descriptive term than Darwin’s “evolution” because it indicates how the process works. Random mutations cause random changes over many generations. The changes that benefit an organism’s proliferation tend to proliferate.

  You know the statement: “Whatever doesn’t kill you makes you stronger.” It should be: “Whatever doesn’t kill you, make you weaker, or leave you the same makes you stronger.” The modified version of the cliché serves as a nice description of natural selection. If a mutation makes you stronger, your progeny stronger, their progeny stronger, and so on, that mutation has a good chance of making it into your gene pool. Mutations that make you stronger are adaptations. If a mutation makes you weaker, and by weaker I mean less competent at survival and/or less competent at reproducing and parenting, it’s not likely to make it out of the gene pool’s shallow end. On the other hand, if it doesn’t make you weaker or if it leaves you more or less just as well equipped to survive and spawn as before, it has a pretty good chance of staying in the gene pool, and maybe somewhere down the line, that mutation might team up with another and the combination could make you stronger. Mutations with this sort of delayed gratification are called exaptations—we’ll get to them later.

  Mutations that make it into the gene pool are “selected” by nature. That sounds nice and tidy, right? Well, random mutations happen to both predator and prey, as well as the landscape itself. Just because a mutation makes you better at reproducing does not mean that it will make it into the pool, because the pool changes too.

  Here’s evolution’s feedback loop: The mutation alters the individual. The individual alters the environment. The environment, including other animals, as well as friends and relatives, determines which mutations benefit a species and which do not. Those that benefit carry on to progeny. The progeny alter the environment, and so on—a picture within a picture.

  Figure 2: The natural selection feedback loop.

  2.2.1 The power of long times and large numbers

  People produce new generations about every twenty years, and tiny random mutations occur every time. Looking around, we see very little change across the four or five generations we’re exposed to during the few decades we live. So if it takes a thousand generations for a significant mutation to proliferate, how long would it take to crank out a whole different beast? Several hundred thousand years equates to tens of thousands of mutations, so that’s the rule-of-thumb timescale for natural selection in humans. The timescale differs for different species. A dog generation is about a tenth of a human generation, so coyotes, wolves, and puppies evolve ten times faster. Most life on earth has a generation that lasts weeks; some bacteria turn over in minutes. With such short generations, biologists and biotechnicians can see adaptations evolve through natural selection in their labs during their lunch breaks.

  Making choices by random chance is no more intelligent than playing the lottery. When a baby is born with a significant mutation, odds are that it will kill him. But with billions of years to work with, millions of random variations easily combine into a hefty list of excellent adaptations.

  You see, evolution enjoys a relaxed timescale. Seriously, Darwin was in no rush. I mean, he’s long dead, but even if he were alive, the dude would still have the long view in mind. We rarely deal with truly large numbers, so it’s no more surprising that we have trouble grasping evolution than that we buy lottery tickets.

  2.2.2 Evolution predicts what already happened

  In physics, theories predict how stuff works. If you kick a football and tell me its direction and speed, I can calculate where it’s going to land. Quantum electrodynamics, while a mouthful, predicts the behavior of hydrogen atoms to a greater precision than anything else human beings have measured.

  Evolution doesn’t predict which mutations will happen. It’s not that kind of theory.

  When presented with a vat of bacteria and details of the chemical soup where it lives, temperature, humidity, and all the other conditions, evolution won’t predict what comes out after one hundred thousand generations. It tells you that whatever survives will be better suited for those conditions than what you started with. It doesn’t predict which mutations will occur, only that the survivors will be better at surviving than their ancestors. Just because a mutation is beneficial doesn’t mean it will happen.

  Any explanation we serve up for how or why an organism has a certain characteristic must be consistent with the rules of natural selection. It’s in this sense that evolution serves as a judge for biological explanations. However—and watch your step here because this is a minefield for biologists, behaviorists, neuroscientists, psychologists, linguists, and philosophers—just because an explanation makes sense in the light of natural selection doesn’t mean it’s right.

  Before continuing, let me be clear that there is no scientific doubt about the reality of evolution through natural selection. It forms the backbone of biology, biochemistry, bioengineering, and pharmacology. You will not find employees at a biotech firm who deny natural selection, and if you do, I would advise against investing.

  2.3 A FROG, A PUPPY, AND RICHARD FEYNMAN WALK INTO YOUR CRANIUM

  Our brains evolved from the bottom up, so it’s tempting to distinguish the three obviously distinct sections of the brain as prehistoric, primitive, and genius—your inner frog, puppy, and Richard Feynman. Neurobiologists assure us that it’s not nearly so simple. At each step in the millions of years of their development, brains have re-optimized their internal wiring. There wouldn’t be much point in putting a Corvette engine in a horse-drawn carriage if you didn’t disconnect the horses, add a transmission, install a killer stereo, and put on some nice tires and wheels. A steering wheel might be nice too.

  We’ll use our modified version of this “triune model” of the brain as a metaphor, not a theory, for how the brain works. Metaphors are great for illustrating scientific concepts, as long as we don’t let those metaphors grow hooves and trample the concepts.

  Starting from where the neck bone connects to the head bone, our inner frog brain is composed of the brainstem and cerebellum. The brainstem is a collection of nerves that controls all the processes we take for granted, like heart rhythm, breathing, and perspiration. The cerebellum, sometimes called the “mini-brain,” sits just above the back of your neck and is a bulbous processor composed of more neurons than you have in the rest of your brain combined. It coordinates your motions from dancing to throwing to raising your beer mug to your mouth on target almost every time.

  Figure 3: The same drawing of a brain as before, but with different labels.

  Your inner frog is, in evolutionary terms, the oldest part of your brain. It delivers and receives information to and from neurons all over your body—tactile sensations of your skin, orgasms, pain, the various biological urges to fill and empty your body and so on.

  2.3.1 First dose of jargon: neurons, axons, dendrites, and synapses

  We’re both pleasantly and painfully aware of the presence of nerves throughout our bodies. Nerves deliver signals to our brains and carry instructions from our brains to our muscles. The spinal cord is the cable through which tactile sensations are received and commands to muscles are transmitted. Every sense has such a cable. The optic and auditory nerves are really bundles of thousands of individual nerves, each carrying a unique signal. It’s the same deal with the sense of smell and its olfactory nerve. Taste is altogether nervier, delivering data from tongue to brain through the facial, glossopharyngeal, and vagus nerves.

  What we think of as nerves are more accurately called neurons. In addition to carrying signals to and
from the brain and body, neurons within our brains form the scratch paper on which we write our thoughts. Like all biological cells, neurons have a cell body that houses the nucleus, chromosomes, and all that stuff from Bio I that we’ve forgotten.

  Axons carry signals from one neuron to another. Your longest axon is the sciatic nerve that runs from your tailbone to your big toe. The shortest are millimeter-or-less connections between neighboring neurons within your brain. Neurons have a single axon for transmitting signals, but they can have a veritable forest of dendrites for receiving signals. One axon can connect to many dendrites, including the dendrites of its own neuron. When a neuron’s axon connects to one of its own dendrites, it feeds back its own signal.

  The cell body is about 30 microns (0.03 mm) across, a bit smaller than the diameter of a human hair. While axons can be quite long, they are about 1 micron (0.001 mm) in width. Dendrites are a little wider than axons, though rarely longer than 50 microns (0.05 mm). The points where an axon connects to a dendrite are called synapses. With the central body or “soma,” the long axon, and the cluster of dendrites about the body, the whole thing looks sort of like a tree.

  Figure 4: A neuron and a synapse.

  2.3.2 Your inner puppy and inner Feynman

  The next layer, your inner puppy, called the limbic system, is made of organ-looking things; stuff like the amygdala, basal ganglia, hypothalamus, and a mess of other individually discernible doodads.

  Your inner puppy is the part of you that likes to play, the part that betrays whether you’re happy or sad, afraid or confident. It wags your tail when you’re happy and perks your ears when you’re fascinated. It’s the part of you that feels appetites like hunger, thirst, and carnal lust.

  The outer layer, your inner Feynman, where you do mathematical physics, make conscious decisions, recognize faces, speak, plan, and develop goals, is the uniform-looking, wrinkly outer layer called the neocortex.

  Richard Feynman was the greatest American physicist of the twentieth century. When he worked on the Manhattan Project he picked locks in top-secret buildings; as a member of the panel assembled by NASA to investigate the Challenger space shuttle explosion, he discovered the engineering mistake by questioning bureaucratic dogma; he gave a series of famous lectures on basic physics that have dazzled every physics major in the last fifty years; and he also made physics far more approachable by describing sub-nuclear processes in cartoons called Feynman diagrams—I’ll show you some later.

  The urge to think of your inner frog/brainstem plus cerebellum, inner puppy/limbic system, and inner Feynman/neocortex as three distinct layers that evolved over different epochs is tempting because, well, it’s more or less how it happened. But puppies have a bit of Feynman and frogs a bit of puppy. That is, amphibians and reptiles may not feel anger per se, but they respond to challenges as though they do, and if a lizard looks pissed off and acts pissed off, I’m willing to assume that it’s pissed off, and being pissed off is an emotion. Similarly, when my dog Professor Buckley figures out how to unlatch the gate or wakes me up with his leash in his mouth, it’s the work of his inner Feynman.

  Your brain divvies up the workload to millions of subnetworks that perform the processes that keep you going. Each subnetwork processor is also a building block for other processors. If the left side of your brain just in front of your ear is damaged, you’ll lose the ability to speak because you have a speech processing unit in that space. However, that processing unit is part of a broad network. To discuss an orphan growing up on northern California ranches, you associate information from other localized subnetworks including those that process how you feel about the kid and whether or not he wept alone or just let the world laugh with him, plus what you know about citrus, geography, and turn-of-the-twentieth-century history. When you get to the oranges, associations from your visual, scent, and taste processors all affect what you have to say and then, finally, you can associate all that baggage with the lower-level motor cortex processor that blows air through the vocal cords of your inner guitar to produce audible speech.

  The vast majority of people, about 95 percent, use the same areas of their brains to perform the same tasks. A guy gets a whack to this part of his head and he can’t talk anymore. Look at his brain after he dies, see the part that’s wrecked, and it must be the inner talker, right? Well, sort of, but not quite.

  Functional nuclear magnetic resonance imaging, fMRI, produces those multicolored pictures of brains that you see in magazines, newspapers, and books, such as those listed in the bibliography. As fMRI techniques have improved, subtle mental processes have been isolated to specific regions of the brain. Reading, writing, and arithmetic processors have been found, though the three Rs require combinations of processors. Facial recognition has been localized to a region of the right brain. And where we store information about movie stars has been narrowed down to several thousand neurons.

  The processing centers in your inner Feynman don’t have clear-cut boundaries the way that organs do, and this is where our frog-puppy-Feynman metaphor runs out of steam. You could cut open my belly, saw my rib cage apart and yank out my heart, liver, pancreas, stomach, gizzard—all that gooey stuff—cut away the inputs and outputs, arteries and veins, and throw each organ in a separate bucket. But what I call processing centers aren’t separate organs. If you cut open my brain, you can’t tell my speech processor from my calculus processor because, as we’ll see, these two processors share subnetworks.

  Your inner Feynman is not composed of individual components that perform separate tasks; it’s a network.

  The left brain has localized clusters of neurons, processing centers that provide higher-level data for association among other processing centers and the entire network as a whole. The right brain has processing centers too, but on the right, the neurons have longer connections that form fewer but bigger and broader subnetworks.

  To color-code it, neuron cell bodies are dark gray. Since the axons that stick out from neurons carry electrical signals, they need insulation just like the wires that go from your MP3 player to your ears. That bio-insulation, called myelin, is white. The left brain is a darker shade of gray than the right brain because it has a larger number of closely packed gray neurons with short axons. The right brain is a paler shade of gray because it has fewer gray neurons with more long-reaching white axons.

  The difference in how the left and right brains are wired indicates their functional difference. The left brain’s localized subnetworks tend to perform more focused processes, and the right brain’s farther-reaching, global subnetworks tend to monitor broad relationships among processes.

  2.4 HOW TO GREET A SABER-TOOTHED TIGER…OR CHESS PLAYER

  Say you’re walking along the street, you turn a corner, and there, towering over you, is a snarling saber-toothed tiger. The sight and smell of it enter your brain and, still barely processed, the data arrive first in your thalamus.

  The thalamus is the part of your inner puppy that acts as a way station for incoming data. Our eyes scan far more objects than we notice. The thalamus is the first step in deciding whether or not the thing in view is worth considering. The thalamus immediately sends the data to your amygdala, which is your four-F center: fight, flight, freeze, or “mate.”

  Your amygdala reacts to the sight, scent, and snarl of the saber-toothed tiger with a blast of fear. The fear triggers an injection of the action hormone epinephrine, which is also known as adrenaline, into your bloodstream. In so doing, the amygdala tells your inner frog to crank up your heart rate, start sweating, and get ready to run, fight, or talk your way out of this mess.

  Vesicles on the axon end of the synapse release neurotransmitters. Neurotransmitters change the shape of receptors on the dendrite, opening a membrane that allows the signal to flow from one neuron to another. Neurohormones and neurotransmitters like epinephrine play a huge role in how we feel about life, the universe, and everything else. When your inner pharmacist doses you with dopamine, for
example, you feel rewarded and satisfied. Endorphins block pain and generate pleasure rather like opiates. Oxytocin and vasopressin make you feel desired and trusting. Serotonin affects your feelings of safety and happiness. Hundreds of others have been identified but their roles are mostly vague, especially in combinations. As with everything in this field, we tread lightly. Just as we don’t all respond to drugs in the same way, we don’t all respond to neurotransmitters in the same way.

  The conscious feeling of fear, or any feeling for that matter, comes after the initiation of your physical response—sweating, trembling, muscle tension. Your brain doesn’t determine that you should be afraid and then generate the feeling of fear; it generates the physical response to fear and that physical response is fed back up to the thalamus and then to the amygdala, which generates the sensation of fear.

  Within about 0.2 seconds of your saber-toothed encounter, your amygdala does two things. First, it engages your flight mechanism and you sprint the hell out of there. Second, it forwards the decision to your forebrain.

  Your visual processors take an additional quarter of a second to refine the image of the saber-toothed tiger. Just after the image is ready for your Feynman to contemplate, your inner puppy’s decision to flee arrives at your Feynman with a dose of hormones that produce a feeling of certainty. The confidence born of that certainty convinces your Feynman that it actually made the decision to flee so that it doesn’t waste time second-guessing your inner puppy instead of getting the hell out of there.