Life Lessons from a Brain Surgeon Read online

  They laughed again at my naiveté.

  But there was no more laughter the next morning, at 7:30 a.m., when I stood across from the surgeon on the other side of an operating table. His patient, lying before us, was covered by a sheet except for the top of his head, which had already been shaved. The surgeon cut the scalp, drilled and cracked open the bone, incised open the dura, and revealed undulating white flesh speckled with tiny blood vessels. For a moment, it felt like a violation. Heart surgery is impressive, but in some ways it’s like working on a car engine: it’s all valves and pistons and fuel lines. But the brain is different.

  Here at the mysterious core of human being, I thought maybe a living person’s skull should be sacred space, taboo to enter.

  That feeling lasted about five seconds. Then came the thrill. If the cranial vault is a sacred sanctuary, so be it: I could become one of those few trusted to enter it. Later that day I let the professors know: I would accept their offer to enter neurosurgical training.

  So began my anatomy lesson like no other. Now please allow me to show you inside my workshop.

  BEYOND THE SKULL

  To begin: the brain doesn’t actually sit inside the skull; it floats, protected by a natural shock absorber called cerebrospinal fluid, or CSF for short. CSF is produced at a rate of about two cups per day from inside the brain’s deep, hidden chambers: the ventricles.

  Although it looks like water, CSF is filled with bioactive ingredients that serve as the brain’s “nourishing liquor.” It carries bioactive factors that keep the brain fit and also drain away the brain’s waste products.

  A weird thing about the brain is its peculiar texture when you touch it. You might assume it’s like a muscle, or body fat — that you could push your finger into it as you would into someone’s belly, and it would smoosh in a little and then rebound. But that’s not how it works. In reality, the texture of the brain is like no other flesh. It’s more like flan or bread pudding. Push your finger against it, and your finger will sink straight in. Take a thimble and you can scoop up an easy million or so brain cells.

  Those cells on the outer lining of the brain, by the way, are the most precious ones. You have probably heard of the cerebral cortex. That’s not just a synonym for the whole brain. The word cortex comes from the same Latin word that gives us cork, which grows on the bark of a type of oak tree. The cerebral cortex is the bark on the brain — incredibly, less than one-fifth of an inch thick — where most of the magic happens in human beings: consciousness, language, perception, thought.

  Visually, the most notable feature of the brain’s surface is how it looks like tightly tucked hills and valleys. Each of the little hills is called a gyrus, with a soft “g.” (So it’s “jie-russ,” not “guy-russ.”)

  The valley or sunken section is called a sulcus, which is pronounced with a hard “c.” (So it’s “sulk us.”)

  The reason for all this folding is that it permits a greater surface area. Unfolded, the cerebral cortex would be the size of an extra-large pizza. The brain wants the most acreage it can get of that thin but powerful cortex, so it figured out a way to fit more of it into the skull, by folding it like an accordion or a pleated curtain.

  What you have to understand about the cortex is that it’s all “gray matter,” the central bodies of brain cells. Under a powerful microscope, these neurons appear to line up vertically like pine trees in a forest. And like the roots of a tree, each neuron has a branched network of thread-like connectors that link to other neurons. These connectors — the biological equivalent of cables — are the “white matter.” Sixty percent of the brain is white matter.

  The incoming fibers that carry messages from other cells are called dendrites. The outgoing fibers that send messages to other cells are called axons. So if one neuron wants to talk with another neuron, it sends an electrical signal down its axon to meet one of the other neuron’s dendrites. But they never physically touch. Think of Michelangelo’s painting in the Sistine Chapel of God and Adam’s fingers reaching toward each other.

  The space between, called a synapse, is where a variety of chemical messages swirl. Those chemical embers, called neurotransmitters, float across the synaptic cleft. There are dozens of these neurotransmitters — some that you might have heard of include dopamine, serotonin, epinephrine, and histamine — and they all have different effects on neuronal communication and function. Put it all together, and you can begin to understand the design that can generate the infinite variety of feeling, thought, and imagination that humans experience.

  NEURO BUSTED: BRAIN CHEMICALS PLAY MANY ROLES

  Some people think of dopamine as the “feel good” neurotransmitter, the one that showers your brain when you are overcome with feelings of love or happiness, or activates with the help of drugs like cocaine. But like all neurotransmitters, it has multiple functions. Yes, dopamine is closely involved in generating subjective feelings of pleasure. But a lack of dopamine in the brain causes Parkinson’s patients to struggle with movement. And when medicines like L-dopa are given to replace deficient dopamine in order to address movement issues, the range of possible side effects are quite revealing. Some patients develop a gambling addiction, and some can become hypersexual. The bottom line is that assigning one feeling or cognitive function to each neurotransmitter is a gross oversimplification. All neurotransmitters — including not only dopamine but also epinephrine, norepinephrine, glutamate, histamine, and many others — play different roles in different parts of the brain.

  But let’s get back to the large map of the brain. Functionally, the cortex is divided into four sections, or lobes, each devoted to a particular set of tasks. Structurally, though — seen from the top — the brain is also divided into a left half and a right half. Connecting the two halves, deep inside the brain, well below the cortex, is the corpus callosum (Latin for “tough body”), a bundle of hundreds of millions of axons. Each of the four lobes, and all the other brain structures located deeper in the brain, exist in pairs, just like your eyes, your ears, and your limbs.

  Let’s start with the lobe most unique to humans: the huge frontal lobe that bulges beneath our foreheads.

  FRONTAL LOBE

  The frontal lobe plays a primary role in motivation and reward-seeking behaviors.

  When you’re carefully paying attention to what your teacher or boss is saying, that’s your frontal lobe at work. Doing math? Frontal lobe. Crossword puzzle? Frontal lobe. Trying to figure out how to handle a former friend who has lately been talking behind your back? The integration of all those feelings, memories, and possible responses requires the quarterbacking of the frontal lobe.

  And when you feel like jumping out of your car and screaming at somebody in a traffic jam, it’s the frontal lobe that’s supposed to step in and say, “Hold up, not worth it.”

  Actually, that kind of complex decision-making and juggling of conflicting possibilities is managed by a section of the frontal lobe called the prefrontal cortex, or PFC. Just like it sounds, the PFC is the most forward-facing part of the frontal lobe. This is where some of our most human faculties lie: planning, personality, rule learning, and other “executive” functions that permit us to live in a complex, nuanced world pummeling us with stimuli.

  Another subsection of the frontal lobe, near the outside edge of your eyebrows, can be found only on one side of your head: the “dominant” hemisphere, usually meaning the left side (if you’re right-handed) but very rarely on the right side (even if you’re left-handed). This section, called Broca’s area, is where your ability to speak resides. In chapter 3, “The Seat of Language,” there is a full description of Broca’s and other nearby areas that control not only the ability to speak but to understand.

  PARIETAL LOBE

  Running just a few inches from the crown of your head back toward the nape of your neck, the parietal lobe controls sensation. In the first half of the twentieth century, a Canadian-American neurosurgeon, Wilder Penfield, mapped exactly which parts
of the parietal lobe correspond to which parts of the body. Using a tiny probe with a forked tip and a minuscule current running between its tines, he tickled the parietal lobes of living, conscious patients who were undergoing brain surgery.

  (It may sound arcane, but we still use awake brain surgery to help patients. It turns out the surface of the brain doesn’t feel. The scalp feels pain, but the surface of the brain has no pain receptors. It relies on its emissaries, the nerves it sends out into the face and the body via the spinal cord. So, if I numb your scalp and open your skull while you’re under, and then taper off the anesthesia, you will wake up groggy, pain-free, and able to let me know if I’m touching something that interferes with your ability to move, talk, see — or anything else.)

  Step by step, Penfield systematically marched up and around the parietal lobe to identify the corresponding feeling of touch, throughout the body. This area felt like someone touched my foot; that area felt like the stroking of a cheek. Penfield surveyed the cartography of the parietal lobe to generate what is today known as the cortical homunculus, or “little human.”

  Notice that just your tongue, lips, and fingers get about as much area in the brain devoted to them as the entire portion of your body below your thighs. No wonder a kiss or caress stirs us.

  Amazingly, more than forty years since Penfield’s death, his maps remain so accurate that we still use them today as a general guide to where the motor and sensation functions are located.

  OCCIPITAL LOBE

  The portion of your brain at the very back of your head is called the occipital lobe, from the Latin roots ob (“behind”) and caput (“head”). It’s the brain’s visual processing center. An injury or stroke to both the left and right occipital lobes causes blindness, even though the eyes work fine.

  Where things get weird is if you injure only the left occipital, or just the right. Depending on where the damage occurs, sometimes the effect on vision is barely noticeable. Occasionally, however, the person develops a manageable condition called homonymous hemianopsia: partial blindness in both eyes but on just the left side of their visual field, or just the right side. They can see fine looking straight ahead, but their peripheral vision is shot.

  TEMPORAL LOBE

  Place a finger one inch above each of your ears. Just below that spot are the two halves of the fourth lobe: the temporal (as in the temples of your head). Not surprisingly, they handle the processing of sounds in general and the understanding of speech in particular.

  Dr. Penfield also used his electric probe to tickle the temporal lobe. When some spots were stimulated, he found, a person would suddenly be unable to understand speech. In other spots, they would have an astonishing variety of sensations: of dreamlike states, of suffocation, burning, falling, déjà vu, even profound spirituality.

  I once used an electrical stimulator on the temporal lobe of a patient who had a tumor deep within it. Seeking to find a spot where I could safely dissect deeper, I stimulated here and there, each time asking what, if anything, he was experiencing.

  “Listening to Kendrick Lamar!” he said at one point. “Kendrick’s rapping!”

  It was so vivid, the man told me, it sounded like I’d turned on a speaker next to his ear.

  DOWN UNDER

  The four lobes we discussed are just the lobes of the cortex, the outermost layer of the brain. Underneath, the axons and dendrites connect and channel the billions of neurons above to each other and to deeper brain structures below. These subcortical structures — those beneath the cortex — serve in part as transit hubs for signals coming from and going to the spinal cord. They modulate and fine-tune those messages.

  NEURO BUSTED: GRAY MATTER ISN’T GRAY

  In the living brain, gray matter isn’t gray, and white matter isn’t white. Those colors appear only in dead brain tissue filled with preservatives. Inside a living brain, “gray” matter is actually a shimmery beige-pink; “white” matter — the axons wrapped with a fatty myelin sheath — is the color of a glistening pearl. Under the bright lights of the operating room, the iridescent surface of the brain is densely punctuated with ruby-red arteries and hyacinth-blue veins.

  The hippocampus sits in the basement of the temporal lobe. Its name derives from its resemblance, first noted by a sixteenth-century Venetian anatomist, to a sea horse (from the Greek hippos, meaning “horse,” and kampos, meaning “sea monster”). There are actually two, below both the left and right temporal lobes, and they are essential for forming new memories.

  Usually, either your left or right hippocampus is dominant, so this redundancy allows us to remove one temporal lobe if you’re having epileptic seizures emanating from it without destroying your ability to remember new people, places, and events. We figure out which side is most dominant by shutting down one side at a time with a temporary paralytic agent, and then we ask you a series of memory questions.

  Scientists first learned the role of the hippocampi due to the tragic case of a man known to the public only as H.M. until after his death in 2008. Henry Molaison had suffered from epilepsy since childhood until, in 1953, at the age of twenty-seven, he underwent an experimental surgery: Parts of his left and right temporal lobes were removed in hopes of eradicating the abnormal electrical discharges causing his epilepsy. They ended up taking both of his hippocampi and surrounding regions. Afterward, he could still form brief, short-term memories (he could, for instance, remember what a person said a minute ago), but not any new long-term memories (an hour later, he remembered nothing of the conversation).

  The amygdala is shaped like an almond, and as with the hippocampi, there are two of them, one on each side of the brain. To visualize where they are located, imagine two lines going straight back from the eyes, each one intersecting a third line going between the ears.

  Unfortunately, this paired structure has gained infamy as the place where fear lives. This tremendous oversimplification is naive and misguided. It arose from press descriptions of a rare disease called Kluver-Busy syndrome, which is marked by a near-total loss of fear after injury to the amygdalae. And while it’s true that the amygdalae do play an important role in fear, they also do so for other positive emotions. It’s not the fear center, but it is an intense emotion hub.

  The thalamus is another paired structure. It’s larger than the other deep-brain structures and sits near the bottom of the brain, atop the brain stem. In the true center of our semispherical brain, it is a large cluster of gray matter that serves as a kind of train station for all the axons passing through on their way to the spinal cord. Here the axons have their signals tweaked; signals being sent to move the muscles are smoothed and refined. Sensations coming from the body, meanwhile, are likewise modulated and sent on the right tracks toward the appropriate corners of our cortex. The thalamus is like the old-school switchboard operators who direct a stream of incoming and outgoing calls to the right place.

  The hypothalamus, located directly below the thalamus, is only the size of a plump grape, but it regulates hormones that control blood pressure, body temperature, growth, and more. It is a no-fly zone during surgery.

  The brain stem lies below everything else, a structure at the bottom and center of the brain that is no thicker than your thumb. If you stuck your finger in your mouth, it would be pointing at the brain stem. From behind, it’s about even with a shirt collar. The brain stem is the portion of the brain that controls basic functions like breathing, sleeping, heart rate, consciousness, and pain sensitivity. Damage it and recovery is impossible. Miracles don’t happen after this area is injured.

  The cerebellum (Latin for “little brain”) lies behind the brain stem, below the rest of the brain, and can be found in all vertebrates. It helps to refine your physical movements, with a particularly strong effect on coordination and timing. Although it was once believed that motor control was the cerebellum’s only function, neuroscientists now understand that it also plays an important role in a variety of mental and emotional functions. Some now
think of it as a “supervised learning machine” that refines thoughts and emotions just as it does movements. As with much of our knowledge about the brain, it’s still TBD.

  BELOW THE NECK

  The brain is always depicted as an isolated organ sitting atop the body like some master controller. In truth, its tentacles reach throughout the body. Thirty-two nerves branch out of the spinal cord, the tail of the brain, and they exit the spine and go into your arms and legs, allowing your brain to sense what your fingertips touch, telling them in turn whether to pick up that grape or toss that stem. Other nerves arise directly from the brain and descend to your heart and your guts to modulate their function, telling them how quickly to pulse and writhe — and, in turn, telling you when you’re feeling so nervous you have “butterflies.”

  The brain’s reach into your body is not only mediated by nerves. The deeper structures in the brain, like the hypothalamus, make master hormone regulators that trigger the nearby pituitary gland to drip hormones into your blood. As these hormones descend from the blood in your brain to your body, they tell the thyroid, adrenals, testicles, and ovaries what to do. All the glands in your body are under the dominion of chemicals released by the pituitary, which hangs underneath your brain just behind the upper bridge of your nose. As with nerves that the brain sends down, hormone levels are detected in reverse order to keep us finely tuned. Disruption is when diseases ensue.

  We still have no clue how consciousness arises from flesh and blood or how the mind arises from matter. We early cartographers of the cranium have made only the roughest of maps. And I can’t wait to find out how the gaps will be filled in.