The Human Brain

The Human Brain

PAGE CONTENTS:

Inside Your Brain

Your Plastic Brain

Inside an Evil Brain

Coffee On the Brain

Inside Your Brain

We humans like to think that our brains are the most complex brains on the planet--that the big, wrinkly cortex of our cerebral hemispheres, which endows us with reason and self-awareness, has made our brains the best. But the longer you study brains and behavior and the animal kingdom, the more you see that each creature's brain is the best for the environmental niche in which it lives.

The much-maligned bird brain has remarkably sophisticated cerebral organization and an amazing flight control system. The shark may have puny cerebral hemispheres, but its brain is an olfactory-processing marvel that lets Jaws live in a perceptual world of smells, and respond like a machine to minute changes in the environment. We can't do that.

But we can think great thoughts, which are important if you're small, naked, and vulnerable in a dangerous world. It's our skill, and our brain is best built to do it. Let's look under the human hood and see how--by touring the big, anatomical brain structures that we can see with the naked eye. Bear in mind that your brain is really much more complicated than this. That's why medical school takes four years, and neuroanatomy is a least favorite subject.

Open the skull and you can look right at the cerebral hemispheres, or neocortex--the "new" part that accounts for most of the mass of big mammalian brains. Alive, the hemispheres are a rosy ecru color, soft--like a well-set pudding. They pulsate in quiet rhythm with your heart.

The brain's surface is a mass of soft, fat folds called gyri, separated by valleys called sulci. The deepest valleys are fissures, and the deepest of all is the interhemispheric fissure--the split down the middle between the left and right hemispheres of the brain. Another one, the Rolandic fissure, divides the front half from the back, and a third one, the Sylvian fissure, divides the top half from each side.

The Frontal Lobes
Fissures are the landmarks that separate the lobes, which are worthy of individual names because they do different jobs. Most of our knowledge about which parts do what comes from studying people with brain injury or illness--people like Phineas Gage, whose face and forehead were impaled by an iron rod. His case helped define the role of the big frontal lobes, which are part chief executive officers, part directors of voluntary movement. They are responsible for ambition and drive, strategic planning, and control of emotional expression.

The Temporal Lobes
On the sides, the temporal lobes are the first way-station for sound processing and memory formation. They gather ideas, and integrate massive amounts of sensory data. The left temporal lobe (in most people) transforms ideas into words for the left frontal lobe to express. In diseased states, the temporal lobes can produce remarkable hallucinations of smells, sounds, and sights, and peculiar states of depersonalization, or absence of the self.

The Occipital Lobes
The occipital lobes are at the back of the brain, mostly on the inside of the two hemispheres, tucked away in the interhemispheric fissure. On the outside, they merge into the back part of the temporal lobes. This part of the brain takes in visual data and processes it, sending it forward to other parts of the brain to be fashioned into recognizable images. When troubled by disease or drugs, the occipital lobes produce hallucinatory misperceptions and illusions.

The Parietal Lobes
Between the frontal lobes and the occipital lobes, and above the temporal lobes, lie the parietal lobes, which map out bodily sensations and do the herculean work of integrating input from all other areas of the neocortex and from the more primitive brain below. They reveal their complexity in the variety of sensory and cognitive symptoms produced by disease. When Alice went down the rabbit hole, she was romping around in her parietal lobes.

The Limbic System
The cerebral hemispheres look like mirror images, but one, usually the left, is in charge of speech and handedness, while the other is more or less in charge of visual-spatial thinking. Split the brain down the middle, along the interhemispheric fissure, and you'll see a big bridge of nerve fibers--the corpus callosum--connecting the two sides. The gyri surrounding it and the deep parts of the brain are part of the "limbic system," one of the least understood brain regions.

Here lie your emotions, tangled up with memory formation, your sense of smell, the regulation of fight-or-flight reactions, hunger, thirst, and temperature. Here are laughter, rage, crying, and pleasure. Here is the border--and the connection--between our brand-new big brain and the little old brain we share with all the other animals.

The Brain Stem
Put your finger at the back of your head, at the notch at the base of your skull, and you'll be just outside the lower end of a jam-packed, finger-sized structure called the brain stem. It is an exquisitely organized, multiple-lane highway for information speeding between the brain above and spinal cord below. Interspersed among the lanes are brain stem nuclei--little traffic control centers for parts of the body. A little damage here can kill, paralyze, or even lock people in, leaving them with no way to communicate that they are still inside.

The top part of the brainstem is the midbrain, the middle part is the pons, and the lower part, which merges into the spinal cord, is the medulla oblongata. In the midbrain, we swallow, hiccup, yawn, and move our eyes--sometimes deliberately, sometimes reflexively. The pons houses the on-off switch for consciousness. And the medulla controls the automatic, life-sustaining rhythm of breathing and influences other crucial, "vegetative" functions like heart rate and digestion.

The Basal Ganglia and Cerebellum
The brain stem swells at its top into big grey globular pieces that connect it to the neocortex. These are the basal ganglia, part of the control system for motor activities. They work in concert with the cerebellum, a delicately convoluted little accessory brain that first appeared in a big way in birds. It's a motor computer that controls the rate, force, and timing of all movements. When you start up a staircase, your cerebellum tells you by the second step exactly how high you must lift your foot to clear this flight's riser height.

The cerebellum is visible at the back of the brain, nestled under the occipital lobes and connected by nerve fibers that wrap around the pons. The basal ganglia and the cerebellum are continuous feedback systems that control the body while the neocortex above tells it what to do.

The brain may be the boss of the body, but like all dictators, it's vulnerable to its vassals, should they fail to serve. The big neocortex demands much energy and will fail quickly if oxygen or glucose doesn't arrive, leaving behind a body driven by an automatic pilot in the tougher old brain--and wiping out much of your "self."

So, where in this incredible organ is the self? No one knows. To the naked eye, the monotonous surface of the brain yields no clue to its phenomenal specialization and organization, or to the self that lies inside. Einstein's brain looks like the one in the guy next door.

--Elizabeth Reid, MD

Your Plastic Brain

We bring you a from-the-front-lines look at what today's scientists are discovering about "neuroplasticity," your brain's ability to change itself. For help, we're turning to Dr. Norman Doidge, author of the bestselling book "The Brain That Changes Itself".

Dr. Doidge explains:

The Discovery of the Century: Your Plastic Brain

Recently I wrote a book about the revolutionary discovery that the human brain can change itself. Without operations or medications, scientists, doctors, and patients have made use of the brain's hitherto unknown ability to change. Some of these people had what were thought to be incurable brain problems; others simply wanted to improve the functioning of their brains or preserve them as they aged.

For 400 years, this venture would have been inconceivable because mainstream medicine and science believed that brain anatomy was fixed. The common wisdom was that after childhood the brain changed only when it began the long process of decline; that when brain cells failed to develop properly, or were injured, or died, they could not be replaced. Nor could the brain ever alter its structure and find a new way to function if part of it was damaged.

The theory of the unchanging brain decreed that people who were born with brain or mental limitations, or who sustained brain damage, would be limited or damaged for life. Scientists who wondered if the healthy brain might be improved or preserved through activity or mental exercise were told not to waste their time.

A neurological nihilism--a sense that treatment for many brain problems was ineffective or even unwarranted--had taken hold, and it spread through our culture, even stunting our view of human nature. Since the brain could not change, human nature, which emerges from it, seemed necessarily fixed and unalterable as well.

The belief that the brain could not change had three major sources: the fact that brain-damaged patients could so rarely make full recoveries; our inability to observe the living brain's microscopic activities; and the idea--dating back to the beginnings of modern science--that the brain is like a glorious machine. And while machines do many extraordinary things, they don't change and grow.

I became interested in the idea of a changing brain because of my work as a research psychiatrist and psychoanalyst. When patients did not progress psychologically as much as hoped, often the conventional medical wisdom was that their problems were deeply "hardwired" into an unchangeable brain. "Hardwiring" was another machine metaphor coming from the idea of the brain as computer hardware, with permanently connected circuits, each designed to perform a specific, unchangeable function.

When I first heard news that the human brain might not be hardwired, I had to investigate and weigh the evidence for myself. I began a series of travels, and in the process I met a band of brilliant scientists, at the frontiers of brain science, who had, in the late 1960s or early 1970s, made a series of unexpected discoveries.

They showed that the brain changed its very structure with each different activity it performed, perfecting its circuits so it was better suited to the task at hand. If certain "parts" failed, then other parts could sometimes take over. The machine metaphor, of the brain as an organ with specialized parts, could not fully account for changes the scientists were seeing. They began to call this fundamental brain property "neuroplasticity."

Neuro is for "neuron," the nerve cells in our brains and nervous systems. Plastic is for "changeable, malleable, modifiable." At first many of the scientists didn't dare use the word "neuroplasticity" in their publications, and their peers belittled them for promoting a fanciful notion.

Yet they persisted, slowly overturning the doctrine of the unchanging brain. They showed that children are not always stuck with the mental abilities they are born with; that the damaged brain can often reorganize itself so that when one part fails, another can often substitute; that if brain cells die, they can at times be replaced; that many "circuits" and even basic reflexes that we think are hardwired are not. One of these scientists even showed that thinking, learning, and acting can turn our genes on or off, thus shaping our brain anatomy and our behavior--surely one of the most extraordinary discoveries of the 20th century.

In the course of my travels I met a scientist who enabled people who had been blind since birth to begin to see, another who enabled the deaf to hear; I spoke with people who had had strokes decades before and had been declared incurable, who were helped to recover with neuroplastic treatments; I met people whose learning disorders were cured and whose IQs were raised; I saw evidence that it is possible for 80-year-olds to sharpen their memories to function the way they did when they were 55. I saw people rewire their brains with their thoughts, to cure previously incurable obsessions and traumas.

The idea that the brain can change its own structure and function through thought and activity is, I believe, the most important alteration in our view of the brain since we first sketched out its basic anatomy and the workings of its basic component, the neuron. Like all revolutions, this one will have profound effects. The neuroplastic revolution has implications for, among other things, our understanding of how love, grief, relationships, learning, addictions, culture, technology, and psychotherapies change our brains.

All of the humanities, social sciences, and physical sciences, insofar as they deal with human nature, are affected, as are all forms of training. All of these disciplines will have to come to terms with the fact of the self-changing brain and with the realization that the architecture of the brain differs from one person to the next and that it changes in the course of our lives. The human brain has underestimated itself.

--Norman Doidge, MD

About the Author
Dr. Doidge is a psychiatrist, psychoanalyst, and researcher, as well as an author, essayist, and poet. His book, "The Brain That Changes Itself", is available at all booksellers.

Inside An Evil Brain

Who knows what evil lurks in the brains of men? Increasingly, the neuroscientists do. In the last few decades, they've made headway in discovering what makes violent criminal minds tick. No scientist claims complete comprehension. In fact, they like to say that if the human brain were simple enough to understand, we'd all be too simple to understand it. Yet their research has shown that bad-guy brains do tend to have a loose biochemical screw.

The average adult brain is 3 pounds (1,400 grams) of unrivaled processing power, with 1 quadrillion synaptic connections organized into various "maps" governing language, movement, vision, hearing, and more. Chemicals called neurotransmitters infuse the whole works and carry messages from one brain cell to another. Two of these neurotransmitters--serotonin and noradrenaline--tend to go wrong in violent people.

Serotonin is the brain's "don't worry, be happy" juice. It's the body's own Prozac. (In fact, Prozac works by helping the brain make use of its serotonin.) At normal levels, serotonin lets the "reasonable" part of your brain maintain control over all sorts of primitive, but pretty useful, drives--like sex, hunger, fear, and aggression.

Of course, serotonin doesn't prevent you from acting on these drives. It just puts the brakes on, giving the reasonable part of your brain enough time to say "back in the cage, monkey boy" or "go for it." Not enough serotonin, and your brain lacks brakes. Drives and emotions rule. Too much, and you're an obsessive-compulsive wreck, agonizing over decisions and details.

If serotonin puts on the brakes, noradrenaline steps on the gas. It's the loyal robot that waves its arms and screams, "Danger! Danger, Will Robinson!" When external events command immediate action, noradrenaline literally focuses the mind, preparing the brain for "fight or flight" decisions and triggering the production of adrenaline and other biochemical concoctions meant to give the body an edge.

Too much noradrenaline, and you're a high-strung hothead stuck on DefCon-2, always ready for a fight. Not enough, and you're one cool cucumber, a daredevil stuntman who needs to jump off bridges to get the rush most folks get saving money at Wal-Mart.

Scientists now know that violent brains tend to have the wrong amount of serotonin and noradrenaline. Low serotonin sets the stage. Without a full set of biochemical brake pads, you're likely to have trouble controlling emotions and drives, including aggression. In fact, when researchers temporarily lowered the amount of serotonin bathing the brains of volunteers at McGill University in Montreal, those volunteers proved far more willing to sting people with electric shocks.

High noradrenaline makes matters even worse. Imagine a brain that lacks emotional brakes and won't drive 55, and you may be imagining an impulsive, violent criminal. Cold-blooded killers seem to represent a special case--a case not of too much noradrenaline but of too little. Studies of convicted murderers in California suggest that serial killers and other remorseless, premeditating sociopaths suffer not from a surfeit of emotions but from a lack of them. Understimulated by life, they tend to kill, literally, for the thrill.

Scientists are quick to point out that none of these biochemical conditions is deterministic. People with low serotonin might find it harder to control their impulses, but that doesn't mean they can't. Nor is everyone with low serotonin and high noradrenaline destined for prison. It takes far more than bad genes to make bad guys. In fact, neuroscientists say that when it comes to the brain, nurture is as important as nature.

Human beings don't contain anywhere near enough genes to build a working brain. It's just too complex. Your genes simply ensure that you get all the mental material you need to get started (and then some, actually). Your brain, interacting with the world around it, has to figure out for itself how to work. Remarkably, it does. Within seconds of a newborn detecting its mother's scent for the first time, neural networks form to make sense of the experience. Such experiences constantly shape your brain.

Those moral lessons from Mom and Dad shaped your brain, too, like so much parental Play-Doh. Infusions of morality affect one part of the brain in particular, the area scientists call your prefrontal lobes (the frontalmost part of your frontal lobes). Just behind your forehead, your prefrontal lobes work hard to keep you from doing stupid things. If shaped and strengthened by good experiences, they add a bit of wisdom to your impulsive desires and help you fit in.

Good prefrontal lobes prioritize incoming information, consider all options, and come up with an endless stream of plan Bs. Those fleeting urges to do or say something you shouldn't all end up here, where you weigh consequences and outcomes and, hopefully, choose to stay on the straight and narrow.

--Michael Himick

Coffee on the Brain

Coffee drinkers will tell you that their brains don't really work until they've had their morning cups. Well, this week, neuroscientists announced that those caffeinated cups may actually protect drinkers' brains--by shoring up a remarkable bit of anatomy known as the blood-brain barrier.

First noticed by doctors more than 100 years ago, the blood-brain barrier is a sort of physiological filtering system inside the tiny capillaries (blood vessels) inside your head. It helps to protect your brain from chemicals and other "foreign bodies" that may be floating in your blood, including things that do you no harm as long as they don't invade your brain.

By allowing only certain tiny molecules to squeeze between protective cells, the blood-brain barrier protects your mental machinery from infection--even as it enables essential communication between your brain and your blood.

"Great," you say, "but what does that have to do with my coffee?" Maybe a lot, especially if your diet isn't perfect. A new study by U.S. researchers suggests that a daily caffeine supplement, equivalent to a single cup of joe, could help keep your blood-brain barrier hale and hearty.

Previous research has shown that high cholesterol can lead to "leaks" in the blood-brain barrier (and may play a role in the development of Alzheimer's disease). Meanwhile, other previous research has pointed to a possible connection between brain health and coffee drinking.

So, for 12 weeks, the researchers fed lab rabbits high-cholesterol diets. They also gave some of their rabbits daily caffeine supplements. Then they tested the rabbits' blood-brain barriers for damage. Result: the caffeinated rabbits had significantly less blood-brain barrier leakage.

Of course, that doesn't mean your doctor is about to start prescribing coffee. But it certainly is food for thought. As the study's lead researcher notes, "caffeine is a safe and readily available drug, and its ability to stabilize the blood-brain barrier means it could have an important part to play in therapies against neurological disorders." Plus, it's one medicine many would find easy to swallow.

--Steve Sampson

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