Conversations with Neils Brain|
The Neural Nature of Thought & Language
Copyright 1994 by William H. Calvin and George A. Ojemann.
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William H. Calvin, Ph.D., is a neurophysiologist on the faculty of the Department of Psychiatry and Behavioral Sciences, University of Washington.
George A. Ojemann, M.D., is a neurosurgeon and neurophysiologist on the faculty of the Department of Neurological Surgery, University of Washington.
A Window to the Brain
THE TIMED SCRUB is an operating room ritual, and Im a little out of practice. Keep those elbows down, I remind myself, so that the water drips off them rather than running the other way, from dirty to clean areas. Scrub, scrub. Three more minutes to go on the scrub, then my grand entrance into the O.R.
Though I have to think about it because I do it so infrequently, this scrub is automatic for a surgeon, requiring as little thought as riding a bicycle. A surgeon gets ten quiet minutes to think about the patient, contemplate the novelties of the case, reflect on what the patient said when asked about preferences. In this type of neurosurgery, there may be a lot of on-the-spot tailoring of the surgery to the unique aspects of the patients brain. And there are often serious value judgments to be made, ones that the patient will have to live with ever after. Conflicts can arise, between getting rid of the patients epileptic seizures and preserving his language and memory abilities intact. One of the neurosurgical principles in such matters is, "Better some seizures than a loss of language abilities." Thats a consideration that could arise later today, when some of Neils brain is being removed.
There is a window next to the scrub sink, and I look into the O.R. to see how things are going. I see the big blue-green tent, created with sterile sheets, but it mostly hides Neil. I remember seeing him at the pre-op conference: the one patient, and twenty inquisitive doctors. Not the usual patient-to-physician ratio, even hereabouts. The conference brings out many people like me who are interested in how the brain normally works, crowding in with the usual specialists in treating epileptics.
Before the conference, when Neil and I were talking about writers, he said that he was becoming a rather specialized kind of writer himself: writing letters-to-the-editor about wearing seat belts. The skull fracture that caused his epilepsy came from a collision with the steering wheel fifteen years ago, during one of those quick trips to the grocery store.
Like most epileptics who are surgical candidates, Neil is highly motivated. A long day of surgery, he said, was nothing compared to coping with a seizure almost every week. And besides, he added, he had always wondered how his brain worked; maybe he might learn a little.
Unlike many of the mentally ill, epileptics often have quite a bit of insight into their problem. Seizures are only temporary, with little in the way of problems between them. A single seizure usually wont hurt you, unless you are driving a car or flying an airplane. Its all the repetitions that make it a serious problem. About one in four epileptics isnt helped by anticonvulsant drugs. If the epileptic "pacemaker" area can be identified, and is in a place where it is doing more harm than good, it can sometimes be surgically removed. This requires a lot of testing, once the brains surface is exposed to the light of day, to identify the troublesome region. The patient wakes up after the first two hours and, under only local anesthetic, works quite hard, exercising his brainpower as we watch his brain.
Another minute. Remember the door. Ordinary pedestrians push open a swinging door in a straightforward manner. Surgeons, however, tend to back into swinging doors, shouldering them aside. No outstretched arms. Ever since I had to learn the surgeons technique for keeping freshly scrubbed hands sterile, Ive been keeping my eyes open around the medical school. Surgeons shoulder doors open, even when not scrubbed. If you watch the people entering a lecture hall, you may be able to sort out the surgeons by their shoulder action.
Toss the brush in the trash without touching anything. Shut off the faucet with its knee control. Peer through the window in the swinging door to make sure that someone isnt about to leave the O.R. Lean your back to the door. Pause. Take a deep breath. Let it out. (No, those arent on the checklist but everyone seems to do it before going onstage.) Back into the door, push it open, and rotate around its edge into the O.R. Another player enters, stage left.
Nobody seems to notice.
THE SPECIAL SIGN hangs on the O.R. door today: "Quiet, Please. Patient Awake."
Thats to cut down on all the shoptalk between
O.R. staff accustomed to anesthetized patients. It was discovered long ago that
awake patients under local anesthesia may not realize
that the nurses are talking about last weeks patient, or the one in the operating room
But its hardly a hushed library. The O.R. is awash in sound. The gurgling sounds emanating from the idling suction, the regular muted beeps from the heart monitor, the chorus of monotonous fans hidden inside a dozen pieces of electronics equipment they go on, not unlike the background sounds of a busy office, but echoing off the tile walls and floors. Theres only one telephone, and the number is unlisted. It seldom rings here, but sometimes the circulating nurse has to answer it and relay a quick question.
Indeed, such a call just caused the second-year resident to strip off her gloves and leave the O.R. a message was relayed from the chief resident, asking for some help down in the emergency room and the surgeon nodded his agreement. She noticed me on her way out, did something of a double take, and then waved at me as she backed through the swinging doors. Wonder whats going on down in the E.R.?
The anteroom was certainly quiet in comparison to the O.R. This isnt my usual milieu. Although Im not exactly a tourist, it always seems a bit of Alice-in-Wonderland when I enter, still wet behind the elbows and dripping occasionally. I never had the slightest interest in becoming a physician, much less a surgeon. I started out to be a physicist, but I soon went astray, seduced by a fascination with the brain. How do you command your hand to grasp a cup? What goes wrong in the brain when your mind fools you? How do you make up a grocery list or plan a career?
I generally work at a desk, surrounded by disorderly piles of scholarly magazines, with a computer or two hidden beneath them. My archaeologist friends smile when they see my office: layers reaching all the way down to physics, they ask? I talk often to anthropologists and linguists and computer scientists about our overlapping interests. And to psychologists and primatologists; Ive recently been creating a computer game for a chimpanzee to play, trying to measure precision timing skills.
Most of the time, I make theoretical models of brain functions lately, Ive been investigating an electrical pattern that I call the "hexagonal mosaics of the mind." But I have little to do with sick people other than when my neurosurgeon and psychiatrist friends invite me to come over and see a patient with a particularly interesting problem. Im a neurophysiologist. Brains how they work, and how they came to evolve occupy my working day.
So what on earth am I doing here in the O.R.? Im about to "assist," lend an extra pair of hands, stand by to solve the minor electronics problems that sometimes arise. And to watch the patient carefully when the neurosurgeon is trying to map out the brains surface the cerebral cortex is, after all, largely what separates the humans from the apes. Weve got four times more.
You seldom get the chance to see a real human brain at least, not while its language cortex is holding a conversation with you. And somehow remembering words, piecing them together into a sentence, picking and choosing which sentence to speak aloud and which to leave in the subconscious to gestate a little longer. A unique person emerges from all that Neil, in this case.
Even more rarely does anyone get a chance to investigate how that sentence comes about. Look for where the names pop out, or where they are strung together into sentences. See what brain areas specialize in reading. Find the spots in the brain where syntax resides, maybe even that "deep structure" that the linguists claim must be built-in.
I wait, hands held high, elbows still threatening to drip one last drop. I finally figured out the change in smell, between the anteroom and the O.R. proper: soap is the primary smell of the anteroom, what with all the scrubbing, but the scent of freshly done laundry dominates the O.R., all of those clean drapes and gowns that have been recently unfolded.
The scrub nurse sees me, but she is busy laying out some sponges for the neurosurgeon. Finally, judging that the neurosurgeon will not run out of sponges for a while, she picks up a sterile towel and walks over to hand it to me. "Lets see, youre seven and a half, if I remember correctly?" That is indeed my glove size. How could she have remembered from so long ago? Ill bet she looked at my hand and guessed.
Once gowned and gloved, I must navigate through all the scattered equipment without touching anything. Hands folded across my chest like a meditating monk or prudent poker player, I work my way around the anesthesiologists gas machine with its air tanks. I catch a glimpse of Neil under the sterile drapes. Only the anesthesiologist can see Neils face. But I can see his arms and legs, and hes restless. Small wonder.
Ive arrived too late to see the first act, appropriately called "opening." Hes lying on his right side so that the left side of his head is up. The left side of Neils brain is where the problem is. To see the relevant part of the brain that is causing Neils epileptic seizures, the surgeon must remove a hand-sized piece of bone, opening a window into the brain just above the line between left eye and left ear. The bone must be taken out in one large chunk, because it will be reinstalled in Neils skull late this afternoon to close that window. Opening is just a matter of drills and saws although especially nice models, ones that any cabinetmaker would covet, designed to avoid damaging the underlying layers.
Opening is consequently a little noisy. Neil got to sleep through it all. But its over now, and the intravenous short-acting anesthetic has been stopped, allowing Neil to wake back up. He needs to be alert during the next act. And there is very little to cause any pain at that stage of the operation. Touching the brains surface doesnt produce any sensations of touch. The brain itself has no sensors for that sort of thing, although it receives messages from sensors elsewhere in the body.
GEORGE OJEMANNS OFFICE will be even more of an archaeologists delight than
my own, with piles everywhere ("My filing system," he claims. "What year did you
loan me that book you need back?"). The patient records are, of course, kept
elsewhere, one reason that he can indulge his filing system.
The neurosurgery operating room, the various consulting rooms in the clinic, the patients hospital rooms, the conference rooms where x-rays are posted and cases are debated theyre all "offices" of a sort for a neurosurgeon, who can wear out a new pair of shoes faster than most of us.
Here in the O.R., the neurosurgeon is like the captain of a ship, navigating difficult waters while directing a cast of thousands (well, a half dozen at the moment). Even the spotlights tend to feature the surgeon although once you get a view of the sterile field and the patients brain, you realize that the surgeon is illuminated only incidentally, backlit by the spotlights and with his face lit by the light reflected from the well-lit brain. Reflected glory, indeed.
"We ought to be ready for the handheld stimulator in a few minutes," George says softly to me as I finally inch my way past the last obstacle. My cue to get busy unwrapping the sterile box of electronics. I signal the circulating nurse to come and help me (brief glances and raised eyebrows are an important mode of communication in the O.R. surgical masks hide most other facial expressions).
"Neil," George continues, raising his voice a bit, "were doing just fine up here. Move around some more if you want to. How do you feel?"
"Im okay," the muffled voice replies from beneath the sterile drapes. "What are you guys doing now?"
"Just anchoring the dura, making things tidy for the next act. There shouldnt be any more discomfort," George says. "I put some local anesthetic down on that spot that hurt, but we wont be touching that region of the dura again for a long time, anyway." The dura is a tough "skin" that covers the brain; usually one can cut or stretch it without the patient noticing, but in other patients a little local anesthetic is needed on the dura as well as the usual dose on the skin incision.
The circulating nurse has unwrapped the first layer of sheets surrounding the electronics box without touching the underlying layer. She steps back and, with a flash of the eyebrows, signals, "Its all yours now." I unfold my sterile hands from my chest for the first time and proceed to remove the second layer of sheets that protect the box. A spotlight up in the gallery above me is repositioned to shine down on the side table where the box sits, gleaming but transparent, the size of an old-fashioned bread box and filled with the unfamiliar.
Indeed, the only two familiar things in the box seem somewhat out of place in the O.R.: an ordinary clipboard and a sharpened yellow pencil. Sterile, of course. I find the handheld stimulator and unwrap the wires. We use it to pass a little electric current through the surface layers of the brain. Once I tried stimulating my arm with current of the same strength, a few milliamperes, and all I felt was a tingle. Not pain.
I turn around to face the patient, watching George finish "tidying up," flushing with sterile saline solution and then sucking it up. Nothing seems to be bleeding anymore. But Neils brain looks white and pink and red, simply because there are so many blood vessels spreading out over its surface. It takes a lot of oxygen to run a brain, and so the brain gets about one-fifth of the bright red blood that the heart pumps.
Looks like a normal brain to me, but Im no expert. And George isnt saying yet. He gently touches the exposed surface here and there, especially in the region closest to Neils left ear. Does Neil feel anything? No.
"Feels normal, so far," George says. Sometimes scarred tissue feels tough, its resilience like a stale marshmallow. Whatever is stirring up the epileptic seizures that begin in that region, it isnt obvious. Still, it could be a tumor or an old scar. The microscope may tell a different story this afternoon. Were rather expecting some old scar tissue, because of Neils skull fracture long ago.
"Notice that central sulcus?" George asks me. I peer more closely at Neils exposed brain surface, searching for the characteristic pattern.
Oops, what central sulcus? I missed that there is a little abnormality after all. The brains surface is folded into a hills-and-valleys arrangement (better known as gyri and sulci) that increases the surface area a matter of some importance since the brains fancier functions are performed only in the "cortical" layers near the surface. The more surface area of cerebral cortex, the more "processing power."
You can seldom see down into the "valleys" (some, such as the sylvian fissure, are quite deep), but you can judge how wide the "hilltop" is. And one hilltop is very wide looks as if the fold we call the central sulcus is simply missing in Neil, at least down near the sylvian fissure where the surgical window gives us a view. Its absence probably means nothing; there is a lot of normal variability.
"You should have stuck around until the end of the pre-op conference," George tells me. "The neuroradiologist waited until the very end of the conference and then said, `Oh, by the way, you might not see the central sulcus, down where youll be operating. No one else had noticed, and shes never going to let us forget it."
Magnetic resonance imaging those magical machines that seem to slice your brain up into a series of images, and without even using x-rays is wonderful for revealing details like that, and an MRI is now part of the preoperative workup. It has considerably reduced the number of surprises in the O.R., at least the ones seen at this stage of the operation. Back when George learned how to do this kind of epilepsy surgery from Arthur Ward, about a quarter century ago, they were lucky to have a good x-ray highlighting the major blood vessels in advance of the surgery, displaced blood vessels serving to warn us if there was a tumor. And back when Arthur learned the epilepsy operation a quarter century before that, in Montreal, from Wilder Penfield himself, much of the time they were flying blind. Penfield was the pioneer, the neurosurgeon whose maps of motor and sensory strip are frequently seen in textbooks, whose reports of memories evoked by brain stimulation have dominated popular accounts of what memories are stored in the brain.
Now there are a number of ways to image the brains anatomy. The computerized tomography scanners started the revolution in the early 1970s. The MRI then came along, improving resolution enough that we can see boundaries between gray matter and white matter. We can see the cortical surface folded into hills and valleys. Yet anatomy doesnt always tell you about function. And how well it works that is whats important. Certainly to Neil, who is about to lose some of his brain on the prospect that this will allow the rest of his brain to perform better. Such operations have been done for over fifty years, with many studies of the patients afterward.
THE HANDHELD STIMULATOR looks like a little penlight that grew a pair of horns. And, of course, a tail that wire trailing back to the electronics. The horns are silver wires that end in smooth little balls. George turns and takes the stimulator from me, double-checking the wiring that the nurse and I have created.
"Neil?" he asks, raising his voice. "All settled down for a while?"
"I suppose so," Neil answers from under the drapes. "Whats next?"
"Now were ready to do some of that electrical stimulation that I told you about yesterday," says George. "I want you to tell me if you feel anything."
George lowers the two silver wires until they gently touch the exposed cortical surface, and then lifts them again. "Feel anything?"
"No. Nothing," replies Neil.
By this time, Ive maneuvered myself back around the anesthesiologists gas machine so that I can peer under the sterile drapes and see Neil a little better. Hes lying on his right side, with his head propped up on a doughnut-shaped pillow. The tent over him has a flat top, created by the scrub nurse for her big tray of instruments, but one side is open. Neil sees me looking at him, and I silently wiggle my eyebrows at him.
"Hey! Someone touched my hand!" Neil volunteers. Neither the anesthesiologist nor I had come anywhere close to Neils hand.
"Which hand?" asks George.
"My right one, sort of like someone brushed the back side of it. Its still tingling a little." The right hand reports to the left side of the brain, and George evidently has located the hand area of somatosensory cortex with the stimulator.
"Turn down the stimulator current a little." George glances up at the technician in the gallery, and a voice comes back over the intercom saying that the stimulator is now set at two milliamperes, down from three.
"Felt it again," Neil reports. "Same place as before. But it isnt continuing to tingle." Neil is picking up on our strategy but then, hes an MIT-trained engineer. And hes been reading a lot about the brain these last few weeks.
"Thats on the side of my face," Neil says. "The right side. Cheek, sort of."
"Does it tingle afterward?" George asks.
"No. Didnt feel normal, though. Funny kind of feeling." Thats par for the course stimulated sensations are seldom identifiable with any familiar sensation. No patient has ever reported being tapped with a pencil point, for example.
Everyone is listening to Neil. There is just the busy background noise of the O.R., with no one speaking. There is a pause in Neils responses, probably because George is stimulating some region that isnt in the primary somatosensory cortex. Most regions of the brain can be briefly stimulated without the patient being aware of it.
George looks up from the sterile field and nods to me. I bend down farther, sterile gloves clutched to sterile chest, and peer intently at Neils hands and face.
"Somebody moved my hand!" Neil says again. "Felt funny, but I sure didnt move it." George must have stimulated the motor strip. Neils hand didnt move in any ordinary way. At first, it looked as if he might be reaching for something, but then the hand rotated to be palm upward, with none of the finger positioning associated with grasping. Motor cortex stimulation seldom produces movements that might be useful.
The motor cortex is just in front of the somatosensory cortex. And if I know George, the next thing to move will be Neils jaw.
Sure enough, I see Neils jaw tighten and the right corner of his mouth pull back a little.
"Felt like the dentist pulling the corner of my mouth back," Neil reports after the stimulation stops. "But not very gracefully," he adds. There is no sense of volition patients dont report wanting to move, and then doing it. These are involuntary movements, and rather uncoordinated ones at that.
"Nothing else," I report, meaning that I didnt see the hand move at the same time. I focus on Neils right thumb, expecting George to try stimulating a point on motor cortex midway between his two previous positions.
And sure enough, Neils right thumb flexes inward. Neil notes that someone is moving his hand again. Although the jaw and the thumb may not be adjacent to one another within the body, the jaws motor cortex patch is adjacent to the one for the thumb.
"Didnt see any jaw movement," I report afterward. Near the boundary, the electrical stimulation may spread enough to evoke both movements.
I didnt see Neils left arm or face move either, although that goes without saying. It would really be newsworthy if I had seen the left side move while the left brain was being stimulated. That the left brain has something to do with the right side of the body was discovered by the ancient Greeks. Hippocrates noticed that injuries to one side of the head often caused the other side of the body to become paralyzed or suffer seizures.
The notion of "maps" on the brain surface has been around for about two centuries. By the early nineteenth century, the phrenologists, such as Franz Joseph Gall in Vienna, proposed that the brain had rather detailed functional maps, even suggesting that there was a separate area for grammar. Phrenology then went down the wrong track with the notion that these maps could be located by feeling the bumps on the skull, and that there were different areas for "Democrats" and for "Republicans." These maps, still popular among artists, are largely wrong but they serve to remind us of how the science got started, with a good idea.
The orderly map on the brains surface representing movement commands has been known for a little more than a century. A British neurologist, John Hughlings Jackson, observed the way an epileptic seizure progressed. The patients tongue might first protrude. Then his face would begin to twitch. Next the fingers, then the arm, and so on to the rest of the body. The slow progression of the seizure served to map the motor strip, much as we do more cleanly with the handheld stimulation in the O.R. The electric current is a crude but effective stimulus to motor strip, so long as you are careful to keep the current strength well below the levels that would start a local seizure.
ON MY RETURN TRIP around the sterile field, I see that big piece of Neils skull,
being kept moist in a protected spot amid the scrub nurses array of instruments and
supplies. Once I get back to stand next to George, I notice that he has placed some
little numbered pieces of sterile paper atop Neils brain, resting lightly on its surface.
Number 1 marks the first site that George stimulated, and so on. The scrub nurse
undoubtedly has kept track of how many have been used, just to make sure that,
along with the sponges, they are all removed later. For now, they serve as
landmarks to remind us of the stimulation results.
Alongside the motor strip, but just to its rear is the sensory strip. In the usual textbook pictures of an average brain, a deep infolded groove, the central sulcus, separates the two maps. But, as our neuroradiologist predicted, Neil doesnt have that anatomical dividing line, at least not down in the region we can see through todays window in the skull. The numbered tags for sensory responses lie right next to the motor response tags, atop the same wide gyrus. No infolded region separates them.
The texts show typical maps of the sensory strip and the motor strip, but patients exhibit a lot of variability. Thats the reason it has to be mapped carefully in each patient undergoing epilepsy surgery. Brain maps are just as variable as faces. No one knows whether such details of cortical organization are important but they might reflect the differences between the clumsy and the well coordinated, the articulate and the tongue-tied.
There are several more motor maps; they are hard to detect in the operating room with the stimulating technique, but are known from laboratory studies of monkey brains. The motor strip, for example, is not the exclusive commander of the muscles. It certainly isnt the exclusive commander of the neurons in the spinal cord that actually run the muscles; the premotor regions just in front of the motor strip have just as many connections down to the spinal cord as does the motor strip itself. But the loss of motor strip tends to produce muscle weakness and, if the damage is extensive enough, paralysis.
Indeed, this is the origin of that dubious factoid: "You use only 20 percent of your brain anyway." This is true, but only in a very limited sense. Before the hand starts acting weak or paralyzed, a slowly growing tumor has to kill about 80 percent of the cells in the hand region of the motor strip. Yet that is a very crude test of function. A pianist or mechanic would probably notice problems long before then. And a stroke that suddenly killed perhaps 30 percent of the neurons in the motor strip would also cause paralysis.
There is more than one map of sensations from the skin, too, and an orderly map of the visual world at the back of the brain losing that piece of the brain causes blindness. But it isnt the only one. No one knows how many visual maps there are in humans, but there are several dozen in monkeys, and more are discovered every year. However important some maps may be (you could be paralyzed or blind without them), we cant think of them as "the center of things" anymore.
Both the sensory and the motor maps extend to include the rest of the body, but those regions are still hidden under Neils skull. The legs and feet are represented up over the top of the cerebral hemisphere, where it turns to dive vertically down the midline.
The representation of the larynx is also inaccessible today, as is most of the auditory cortex, because theyre buried in the depths of that big infolding called the sylvian fissure. The maps of visual space are in the back of the head, quite inaccessible except when a tumor must be removed from there. The only parts of Neils brain that are visible today, because of the surgery he requires, are the left temporal lobe and some parts of the frontal and parietal lobes. But thats a very interesting area it includes most of the language cortex.
I notice George lightly touching the temporal lobe, exploring for scar tissue once more. And since Neil is busy talking to the anesthesiologist and wont hear me, I risk a little computer joke in a soft voice. "Still trying to find the reset button?"
"No," quips George, just as quietly. "Im looking for the seat of consciousness."
Definitely an in-group joke, neurological variety. There is no seat of consciousness. Or at least not of the most interesting aspect of consciousness.
CONSCIOUSNESS certainly seems to be the Big Question. Wheres Neil? Is he down in his brain stem, since thats what keeps him awake? Poking around down there is fraught with hazards the patient might stop breathing, or his blood pressure might soar.
Or is he in his thalamus, since it helps determine what he pays attention to?
Or here in the language areas of his brain, so visible now, that allow him to express himself in ways that chimpanzees cant? It will take at least three chapters in this book to describe how a voice arises from brain mechanisms.
Or is he up in his frontal lobes, which he uses for speculating and worrying and planning? Its what he used to decide whether or not to undergo this surgery today.
Is there a "command neuron" among the billions of nerve cells in his brain that triggers a particular action, or a cell whose specialty is representing his grandmother?
Is Neil "conscious" when he answers accurately but cannot form a memory of the event? Indeed, how does Neil memorize something? And perceive his world, select what to recall from memory, then decide how to act?
How does he create something new, a novel sentence that hes never spoken before, or a plan for a career? Or (the flip side of frontal lobe functions, which we will consider in a later chapter), how would he get sidetracked into obsession, or suffer hallucinations?
And, finally, how does Neil manage to put all of this together, to see himself in terms of the stories that he has constructed about his past? How does he see himself poised at the intersection between his various stories about the past and his various imagined futures? And choose from among them? That, surely, is conscious.
A "voice" emerges somehow, somewhere in that brain before us. It mostly talks to itself (and what does that mean?). It narrates his life story. It is the voice of Neil. He didnt have it when he was born, but he was telling himself stories by the age of four and his inner voice was full blown before he reached his fifth birthday. How did he create it? In the course of this attempt to cure Neils seizures, we will explore Neils brain and learn something about how it creates his unique voice.
Conversations with Neil's Brain: |
The Neural Nature of Thought and Language (Addison-Wesley, 1994), co-authored with my neurosurgeon colleague, George Ojemann. It's a tour of the human cerebral cortex, conducted from the operating room, and has been on the New Scientist bestseller list of science books. It is suitable for biology and cognitive neuroscience supplementary reading lists. ISBN 0-201-48337-8.
|AVAILABILITY widespread (softcover, US$12).|