|A book by|
William H. Calvin
UNIVERSITY OF WASHINGTON
SEATTLE, WASHINGTON 98195-1800 USA
The Cerebral Symphony|
Seashore Reflections on the
Structure of Consciousness
Copyright ©1989 by William H. Calvin.
You may download this for personal reading but may not redistribute or archive without permission (exception: teachers should feel free to print out a chapter and photocopy it for students).
Orchestrating the Stream of Consciousness:
We drove further out the Cape today, and with considerable caution, too, particularly after we came upon an accident in a blind curve, a smashed-up car nosed into a tree and blocking the opposite lane; a truck was stopped just past it. The accident had evidently just happened, and I looked quickly for injured persons needing help. But there was no one in the damaged car, and the truck driver was walking along the shoulder, looking like business-as-usual.
After my second incredulous look at the truck, I figured out what had happened: The flatbed truck held three damaged (and partly flattened) junk cars, two in front (one perched atop the other) but there was only one car at the rear. The car on the road had evidently fallen off its precarious perch atop the other junk car when rounding the curve. And dropped down into the opposite lane of traffic fortunately unoccupied at that particular moment and rolled over, finally coming to rest against the tree. If the driver was worried about being jailed for recklessly endangering other drivers via his improperly secured load, he sure didnt look it. "No problem, no problem!" his expression seemed to say. Evidently, this sort of thing is not taken very seriously around here.
We may not hold animals responsible for failures to look ahead; we realize that their brains are not capable of the foresight that ours are. We do expect operators of dangerous equipment to uphold a high standard in that department. I have no idea what the general standards are among Massachusetts truck drivers, but anyone driving around Cape Cod for a day can see for themselves the standards among the public officials responsible for the roads. The roads are well paved but poorly designed and not just because blind curves havent been straightened out since the horse-and-buggy days.
Like a haunted-house movie, some situations contain so many traps for the unwary as to seem quite unnatural. The Mid-Cape Highway, Cape Cods only modern limited-access highway, is a good idea but with fatal flaws that have never been corrected. At one point in the eastbound lanes just before the Hyannis exit, there is a hill that crests so sharply that the driver cannot see more than a few car-lengths ahead, suggesting that one should slow down to half the speed limit in order to be able to stop for anything on the road (few drivers do).
Thats bad enough. But it is also at the end of a blind curve. And it is where the highway designers chose to locate a rest area of the block-long, extra-wide-shoulders variety, so that cars enter the high-speed lanes from a variety of places (there are two more rest areas in the next few miles, so this wasnt the only possible location). Having eliminated blind intersections with the limited access design, they seem to have recreated a few for old times sake.
Even more incredibly, they put such rest areas on both sides of the eastbound lanes, facing each other across this blind stretch of two-lane hilltop highway, tempting people out stretching their legs on the right shoulder to walk across the highway in search of a rest room (indeed, there is a flight of stairs and a paved path leading off into the median, seemingly promising facilities somewhere near the westbound lanes). In the middle of the road, the pedestrians are likely to see a speeding car rising up out of invisibility, coming out of the blind curve.
Such compounded asking for trouble isnt a failure of the Pilgrims to look ahead to motor-cars: It is the stupidity of recent generations. Not just the designers either, but the politicians who fail to fix it and the voters whose priorities run to "well paved" rather than "well designed." At least such are the dark thoughts that one tends to think while cautiously navigating their highways and contemplating foresight as a defining characteristic of post-ape brain evolution.
Evolution, you may say, surely does better just by trial and error. Just think of those sleek cormorants, swallowing a fish with a deft flip of the head. But, alas, evolutionary design is full of stupidities too, such as our nearsightedness and sore backs. Biological evolution at least has the excuse of lacking foresight; one expects better of human cultural evolution.
DWELLING UPON STUPIDITIES, much as I dislike doing it, is a valuable exercise when
thinking about human evolution, as we have a tendency to portray the grand process as perfecting
things, with humans as the pinnacle of progress. Those who no longer believe that humans were
designed according to some grand plan still have a tendency to substitute the evolutionary
process as some guarantee that humans were, nonetheless, well designed. Or at least pretested.|
But there is no reason to assume that humans are any better prepared for our present world than is the skunk, with its striking vulnerability to speeding cars. Nature is full of examples of "good enough engineering" where a sufficient solution to a problem (say, the cormorant wing-flapping to fluff up waterlogged feathers) tends to remove the problem from exposure to further selection pressures that might evolve a better design (such as the ducks waterproofing oil glands). Much evolutionary progress is far too slow and iffy to do us much good: Despite the undoubted importance of good vision for survival, human evolution has somehow let nearsightedness continue in a considerable proportion of the population. This optical myopia has, over the generations, been even more stupid than the metaphoric myopia of the Massachusetts road builders. And cultural evolution has given us eyeglasses only in the last dozen generations, of the hundred-thousand since the brain started enlarging and making lots of tools.
One might think that the skunk-cormorant style of behavioral choice would have been a "good enough" solution to the problems of deciding what to do next. And that little improvements in foresight might have landed their possessor in as much trouble as they avoided. Which all makes the evolution of foresight at least via standard darwinian always-getting-better improvements a bit problematic, not at all the straightforward course of evolution that it initially seems. So what scaffolding, or conversion of function, might have aided foresight? Or what new niche might we have invented that made natural selection so weak that the usual niche-confining rules were suspended for long enough that some rule-breaking exceptions evolved?
A major clue to such inquiries is the human brain itself, looking at what functions are located next to others. And a traditional way of investigating brain organization is seeing what goes wrong, when it does as it recently did to a friend of ours.
OUR FRIEND ELAINE lives out near Wellfleets literary colony, along a protected
stretch of waterway. Escaping from the car, we joined Elaine and all walked along the
waterfront. "Big Blue" flies by every so often, Elaines name for the Great Blue Heron
that inhabits the place, along with numerous cormorants. The first time that you see Big Blue
gliding along, you think that youve seen a hang glider until he begins flapping his
wings in that graceful beat.|
Along the "river," one sees horseshoe crabs scurrying along the sandy bottom. Prehistoric tanks? Imagine a parade float, its wide skirts completely covering the truck that is underneath. Battle tanks were once made this way, to shield their vulnerable treads, but all that extra iron made them too slow and cumbersome. Yet thats the strategy evolution tried to protect the underside of Limulus polyphemus, and it seems to have worked for a very long time: Limulus is a "living fossil," very similar species being seen in the fossil record for the last 350 million years, even back before mammals invented themselves. Settled into the sandy bottom, the crablike legs of the horseshoe crab are completely concealed by the broad skirt of the shell; it almost looks like a bony version of a ray, hiding there in the sand. When it gets up and moves on, it leaves behind a horseshoe-shaped imprint in the sandy bottom. Its no crab, but rather a close relative of the modern spiders; they live from Maine to the Yucatán, and there are three other species in the Orient.
We havent seen Elaine since she was severely injured in a car accident several years ago. An oncoming car swerved across the center line and crashed into her car head-on; the other driver was killed. It was fortunate that, through long habit, Elaine was wearing her seat belt, or there might have been two fatalities. Still, she was unconscious for a week with a severe head injury from the sudden stop, not to mention a shattered hip and ruptured spleen. And it was another month before she knew where she was ("oriented to time and place," as the neurologists say). Except for getting used to the reconstructed hip, Elaine is back to normal now, but it was a long two years of hospitals and rehabilitation therapy ("Try to imagine spending two years in a prisoner-of-war camp," she says, "unable to do anything that you really want to do").
Her friends have told her some of the stories of how she talked during her amnesiac period, while in traction.
"Did you have any visitors today?"
"Oh, yes lots of visitors," Elaine would reply.
"What were their names?"
"Well, there were Adam and Eve. And the Magi too," Elaine said.
"Youre kidding me."
"Oh, no. The Magi really were here," and Elaine went on to give their names.
At one point, Elaine asked one of the hospital staff if she personally knew anyone who had been in the California Gold Rush of 1848. Elaine insisted that she herself knew some veterans of it.
As she got better at recognizing people, she was always introducing arriving visitors to the ones already there, as if she were a cocktail-party hostess. She would often get the name right, but sometimes describe the person inaccurately; an antique dealer became the head of the water department, and she described her surgeon at one point as a merchant from Boston.
The stories she told in her amnesic period in the hospital sound much like my nighttime dreams, always changing direction in midstream to explore a new avenue. One recollection of Elaines shows the dreamlike string of concepts particularly clearly:
A friend brought me a present a small painting of sand dunes to hang at the foot of my bed. I was in traction for several months and always looking at that one spot, being unable to move. When people would visit, I would describe the painting which features a tall sand dune towering above a sandy beach like an art dealer would, saying who painted it and when. But then I would tell them that it showed an island off of Hyannis, that the name of the island was Calypso. I told them that an island gets its name from a ship that has gone aground there, and that a ship named Calypso had run aground on this island. Id draw their attention to the top of the sand dune and say that there was a hole in it, and that if they put their ear down to the hole, theyd hear the ocean surf.
THE PROBLEM with investigating how the brain makes up sequences of mental constructs,
such as our plans for what well do for our next act, is that we are ordinarily quite good at
making logical plans. But when the brain isnt working well, we can sometimes see
flawed sequences being rearranged and improved. And they involve phenomena much the same
as we can recall from dreams when we awake in the morning: In spite of a dreams
resemblance to a scenario or narrative, there are all those strange juxtapositions. Compare
Elaines story with a description of the typical nocturnal dream that we all experience:
Persons, places, and time change suddenly, without notice. There may be abrupt jumps, cuts, and interpolations. There may be fusions: impossible combinations of people, places, times, and activity abound. Other natural laws are disobeyed, and sometimes pleasantly so: gravity can be overcome in the sensational flying dream.Indeed, the typical content of a dream, were we instead awake and without brain injury, would qualify us as mad (they constitute the symptoms of delirium, dementia, and psychosis). The fact that our brains engage in such fantasy for several hours every night suggests that maybe fantasy is its normal mode of operation, that we avoid the slipshod scenarios (when both awake and sane) only by a sustained process of editing out the nonsense, shaping up the imagined scenarios into a thing of quality by a process analogous to the way that bacterium converges on the morsel of food.
Inserting something wrong into a sequence can be readily seen in the amnesia that follows a head injury (indeed, the presence of memory problems is your basic definition of a "concussion"). Sometimes the patient will simply say that he cant recall, but often hell just recall the wrong thing. The textbook examples are the patients who confabulate, the neurologists word for "making up stories" when you cant remember what really happened. A patient with a head injury, when asked what he had for breakfast that morning, may tell a plausible story of fixing bacon and eggs for himself as he usually does at home but, in fact, he ate in a hotel that morning. And hes forgotten about the hotel too. Patients often recover their memories in clusters, and gaps will remain between two accurately recalled events. Into such a gap, the patient may insert another plausible story that didnt really happen. Were always making up stories, I suspect, and relating only the best candidate which is, if things are going well, the true story.
The patients who confabulate arent lying, in the usual sense of the word. They probably relate the best story that they were able to construct from the data available to them and think it true; all their lives, the best candidate scenario has been pretty reliable. Theyre not as bad off as the normal person during a nocturnal dream, making all sorts of inappropriate juxtapositions of people and places; indeed, mild cases of confabulation are near the opposite end of the spectrum, almost perfect except for that one little unknowing substitution.
It shows you that our memories are not like tape recordings which keep the events in an immutable sequence; we remember the elements by recognition, and recall the sequence by ties between those elements. But each recognized element has usually been seen before, and combinations have likely occurred in various orders, and so our memories of individual episodes are often jumbled and unreliable unless weve made a special effort to keep things in the right order, as may happen if we are trained observers such as football referees. But, as the instant television replay sometimes shows, even trained observers get things wrong. Our brains just werent designed to be tape recorders despite their obvious penchant for chaining things together.
THE FOREMOST SIGN OF FRONTAL LOBE INJURY is surely distractibility: You set out to
say something or do something, and you can get easily distracted into saying or doing something
else. The ability to maintain a mental agenda disappears. That certainly fits Elaines
condition during that first month after she came out of coma as in that dreamlike
sequence where she shifted from subject to subject in talking about the little painting. And her
confabulation, such as filling in Adam and Eve when she couldnt recall her earlier
visitors, is characteristic of injuries to the inner surface of the frontal lobes, where the left and
right halves face each other behind the forehead.|
Neurologists are the great natural historians of our day, not only helping the patient but collecting illuminating case histories in the way that Charles Darwin collected bugs in his youth. And then they think about the patterns that emerge from the array of symptoms and injury locations. None has hit the jackpot in quite the manner that Darwin did when he figured out how new species evolve from old ones, but in the century since the beginning of neurology a picture of the frontal lobe has gradually emerged. Most scientists lack the temperament for such a demanding task, instead focusing on quick-payoff investigations that take things apart into their component parts and then take apart those parts too. But frontal lobe is all about putting things together, and the sum is often something quite different from the collection of parts.
Still, there is no point in waving ones hands and ignoring the known subdivisions of the frontal lobe. Its very useful to know that confabulations occur only with injuries to the frontal lobes inside surfaces and not to injuries to the side or top of the frontal lobe. Which, of course, brings up the question: well, what does the rest of the frontal lobe do? For that, one must look for patients who have a small tumor or suffered a blockage of a small blood vessel; people with head injuries, like Elaine, are always injured in multiple places, usually making it difficult to sort out what symptom comes from which place. A. R. Luria, the great Soviet neuropsychologist (1902-1977), pieced together the stories and lesions of a great many patients. Clearly, there are three major functional subdivisions of the frontal lobe: the motor strip itself, the premotor areas, and the terra incognita in front of them, including the prefrontal cortex.
MOTOR STRIP is at the back boundary of frontal lobe, a bit in front of your ear. Injuries there
result in muscle weakness or, when damage is extensive enough, paralysis. There is a map of the
body surface, though upside down in some sense: Starting nearest your ear is the machinery for
throat and tongue and face, then fingers and hand and arm, with the trunk arching up over the
fold down over onto the midline surface of the hemisphere, with legs and feet thereafter. But it
doesnt follow that someone paralysed on his entire right body has a big injury to the
motor strip; someone with a weak right arm and right leg likely was injured where a bundle of
the "wires" (we call them axons) emerging from motor strip pass through a bottleneck in the
lower reaches of the brain and so even the blockage of a small blood vessel there can
affect both an arm and a leg. Someone with no leg problems, but a sagging right face and weak
right hand thats likely a person with an injury to the left hemispheres
motor strip, usually from a blockage of part of the middle cerebral artery supplying the motor
strip with oxygen.|
But nowhere else in frontal lobe will an injury cause paralysis: Damage to premotor and prefrontal regions is much more subtle, more like Elaines confabulation and distractibility. And the farther forward we go, the closer we seem to get to the machinery we use to change from one behavior to another: our versions of the skunks problem of deciding whether to sniff my foot again or waddle off down the street, or the cormorants decision whether to go foraging underwater again or dry its wings a little longer.
PREMOTOR CORTEX is just in front of the motor strip, though the portion on the middle side
of the hemisphere (in front of the legs muscle controller) often gets called the
supplementary motor cortex instead. It too has a "map" of the body indeed, three of
them, arm in front of leg in each case. And unlike the motor strip where the left hemisphere
controls the right body and the right hemisphere the left body, the left premotor cortex has the
reputation of controlling both sides of the body to a much greater extent than right premotor
does. The lateral portion just in front of the motor strips area for mouth and face is called
Premotor isnt "pre" in the sense of its output funneling into motor strip and then down to spinal cord motorneurons; premotor has as many direct connections to spinal cord as motor strip does, as well as feeding into motor strip. It has extensive connections to parietal lobe (and thus information about body image and other spatial matters) and to ventral thalamus (and thus basal ganglia, another major component of the movement-control system) that motor strip doesnt. If you imagine making finger movements (but dont actually move), premotor works a lot harder than the rest of the brain; if you then actually move, motor strip also becomes active. Patients with strokes injuring supplementary motor cortex usually have trouble with such willed movements as speech and gestures. But attempts to fit premotor cortex into a hierarchy have failed; movement decisions dont start there and move on to motor strip. The best rationale that I know for naming it "pre" is because it lies in front of motor strip.
It specializes in setting up sequences of actions, as when you insert a key into the lock, turn it, turn the doorknob, and finally push open the door. Patients with damage only to left premotor cortex will be able to perform each action separately there is no inability to move, as in motor strip injuries but will have trouble chaining the actions together into a fluent motion, what Luria called a "kinetic melody." When we practice playing the piano, or practice our tennis serve or golf drive, we are tuning up the premotor cortex, particularly the left one (in right-handers and most left-handers).
Indeed, to tap your fingers rapidly is a typical request made by a neurologist who wants to check out premotor performance. Sometimes patients with premotor problems cannot easily change from one rhythm to another; asked to draw a sawtooth line and then change in the midst of the task to making square corners or smooth arches, the patient may be able to do each pattern separately but not switch back and forth between patterns. Premotor cortex is all about setting up sequences, chaining movements together. Musicians couldnt do without it.
THE STAGE OF LILLIE AUDITORIUM is not unaccustomed to white dinner jackets; at some
of the Friday night lectures, the person introducing the evenings scientific speaker will
come so-attired. And it is usually a sign that some mischief is planned (baby pictures of the
speaker may be shown at some point during the introduction, or the prediction read from his high
school yearbook); the introductions are often as memorable as the speech that follows.|
But tonight there are multiple dinner jackets on stage. And it has multiple music stands rather than a single podium. The fancy blackboard has also been removed, to permit eight performers at a time on the stage for the final work, J. S. Bachs "Brandenburg Concerto No. 4." And the six players needed for the world premiere of Ezra Ladermans "MBL Suite," commissioned to commemorate MBLs first hundred years. All of the four works on the program tonight feature at least one flute, if not two.
The featured flutist (and probably the reason that the fifty-dollar benefit tickets sold out in only ninety minutes when they went on sale five weeks ago) is Jean-Pierre Rampal. And the second flutist is Jelle Atema, once a student of Rampals in Nice but for the last two decades a biologist at MBL studying the world of odors utilized by lobsters, fish, moths, dogs, bees, and other animals that live in a rich world of characteristic smells. When not in the lab, Atema may be conducting the Falmouth Chamber Orchestra.
But there is no conductor tonight, and I miss seeing those body movements synchronized with the music, fond as I am of conducting the Hallelujah Chorus from Handels "Messiah" from recordings. So I thought that the evening was stolen by Julie Rosenfeld, the first violinist with the Colorado Quartet (which formed the nucleus of tonights group of performers), particularly her performance of the "Brandenburg." A violinist playing such an energetic piece is always interesting to watch, as the instrument almost becomes part of her body, as glued as her head is to the violins sounding board.
If you know your neurology of sequential movements, you realize that the music is flowing from the left frontal lobe, just above that chin on the sounding board of the violin, out the right arm holding the bow, and then back to the performers left side, where left hand, violin, chin, and left brain all resonate in synchrony. That dramatic bowing movement of right arm, and the quick fingering by the left hand, is all focussed on that left-sided resonance, as are the performers eyes staring down at the string and the fingering. The violinists bow is often said to "behave like an extension of her right arm" but the real simile is that arms and violin behave like an extension of her brain, the part of her left brain that is just above the chin rest.
And where in evolution did we get such capabilities? Surely our musical abilities are unlikely to have been shaped up by usefulness. But if the left-brain sequencing abilities were shaped up by something else more closely related to making a living, perhaps music can use those sequencers in the spare time.
THE LIBRARY of the Marine Biological Lab is on the floor above the auditorium; it is now
amalgamated with that of WHOI and is one of the worlds better libraries for basic
biological science. Many books have been written in its carrels and little offices (theres
something about the smell of books that puts one in the right mood for such labors). It is
certainly one of the nicest of libraries, being open day and night; the only other library where I
can reliably check out a book at three in the morning is also at a marine lab, the one at Friday
The MBL library is, however, not the place to read up on frontal lobe injuries and many other matters medical, once you want more than the standard textbook physiology. But since the library of Harvard Medical School was where I was first introduced to such neurological matters, I ventured up to Boston in search of some of Elaines symptoms. And wound up reading Donald Stuss and Frank Bensons little book The Frontal Lobes.
Prefrontal cortex is the front of the frontal lobe, most everything in front of the better-known portions of frontal lobe, premotor and motor strip. Some animals, such as the dolphins, have relatively little prefrontal cortex. Perhaps the best-known function of prefrontal cortex is strategy: Deciding which movement sequences to activate, and evaluating the results. "Getting stuck" with a strategy that no longer works can be a symptom of prefrontal problems. The standard way in which the neuropsychologists test this is with a special deck of cards, though a standard deck of playing cards will suffice: The patient is handed a shuffled deck of cards and asked to sort them into two piles. But on what basis, which cards go in the left pile, which in the right? Ah, thats what the patient has to figure out, based on trying a scheme and the doctor saying "yes" or "no" after each card is laid down. Pretty soon the patient gets the idea that the doctor wants all the red cards in the left pile, all the black cards in the right one, and so zips along getting one "yes" after another.
But all of a sudden, the patient starts hearing "no" and then another "no" the doctor has, without warning, changed the name of the game in midstream. Most patients get the idea that there is a new strategy to discover, and most will figure out within a half-dozen cards that what the doctor now wants is for all the face cards to be put in the left pile, the numbered cards in the right one. But patients with prefrontal injuries often will not change strategies theyll figure out the first strategy, but they wont change strategies when the first one no longer works. They get stuck, obstinately persevering, despite a long string of "no" responses. Monitoring the success of a strategy is something that prefrontal cortex seems to do for us.
Another prefrontal function is helping get sequences in the right order for the premotor cortex to execute. For example, a patient is in bed with his arms under the covers. He is asked to raise his arm. He doesnt seem able to do so. But if you ask him to remove his arm from under the covers, he can do that. If you then ask him to raise it up and down in the air, he does it all correctly and smoothly. Again no motor-strip-like paralysis, and no premotor-like difficulty with executing a fluent sequence just a difficulty in planning the sequence, getting stuck on the condition of working around the obstacle of the confining bedcovers. Prefrontal problems give patients such difficulties in unfolding a proper sequence of actions. This isnt a conceptual problem, since the patient could probably look at another similar patient and analyze his difficulty, yet not be able to unfold the proper sequence himself.
Storytelling that meanders (more than usual!) can be another sign of prefrontal trouble, especially with damage to the bottom surface of the frontal lobe. Elaines meandering story was not unlike a dreams wandering quality, making one wonder if sleep shuts down the orbital frontal cortex. But more than just storytelling, prefrontal cortex seems to monitor narratives, help keep things on track in spite of distractions.
And, of course, we tell stories to ourselves: The narrator of our conscious experience is the "self" we so prize, following its development in the third year of life. "Our need for chronological and causal connection defines and limits us helps to make us what we are," in the words of one literary school. Stories about the past help us to understand patterns of causation; we "analyze" what happened, and so we can experience regret for doing the "wrong thing." Stories about the future help us to plan an agenda for the days activities, as well as a career; we can anticipate in much more detail than other animals, largely because of the chains of possible events that we string together in our heads.
Things can go wrong with this storytelling not merely erroneous stories, but excessive attention paid to this narration. Worry is the most common problem, the unproductive repetition of an imagined scenario. "Getting stuck" on a regular basis is indeed associated with excessive metabolic activity in frontal lobes and basal ganglia as we "spin our wheels."
Patients with obsessive-compulsive disorder have a tendency to be overabstract and overintellectual, to worry and plan excessively for the future, and to repeat serial-sequential behaviors (that is, compulsions) as if locked into a "do-loop" that they are unable to escape.Nancy Andreasen is always kidding her psychoanalytically inclined colleagues that they ought to stop talking about patients with overdeveloped egos and start talking instead of patients with overdeveloped (or at least hyperactive) frontal lobes. Patients with obsessions (such as a paralyzing fear that keeps them from being able to leave their room) or compulsions (such as those patients who have to wash their hands every few minutes) indeed illustrate in extreme degree those very things that frontal lobes are supposed to do for us: think ahead and organize serial movements. Such people often seem "stuck in a loop" and unable to move on to other behaviors.
The imaging methods that allow us to see how hard various regions of the brain are working now show that such obsessive-compulsives have midline frontal lobe regions that are indeed working overtime, compared to the rest of their brains and to normal brains. Normal people increase their frontal-lobe activity when challenged with such serial tasks as the Tower of London game, where one has to imagine how to rearrange rings on a series of posts in order to get them all on one post with as few manipulations as possible. Schizophrenics, on the contrary, do not increase their frontal lobe activity though some, such as those in catatonia, may have high resting levels of metabolic activity, spinning their wheels again.
Some schizophrenics have the so-called "positive symptoms": They hallucinate, seeing things that arent there. They may have delusions, thinking that God is out to punish them. Some have bizarre behaviors or thought disorders. Such patients are often helped by the antischizophrenic drugs and may spontaneously improve as well. These probably arent primarily frontal lobe disorders; disorders of subcortical structures (such as basal ganglia and amygdala) come to mind, as does temporal lobe.
The schizophrenics with "negative symptoms" are the ones likely to suffer from a frontal lobe disorder. These people are drastically slowed down in their thought and speech, have blunted emotions (they dont even smile back at you when you greet them) and seem unable to enjoy anything in life. They seem unable to express empathy with others, and their attention spans may be shortened. There are many other sources of some such symptoms (garden-variety depressions, for example); the combination of symptoms that the psychiatrists associate with schizophrenia by a process of elimination, however, have a poorer prognosis and they often have structural brain abnormalities, such as enlarged reservoirs (known as the lateral ventricles) for cerebrospinal fluid.
Variations in brain structure are not necessarily a problem. For example, normal dizygotic "fraternal" twins have ventricular sizes that are about 50 percent larger than the general population (crowding in utero makes twins more vulnerable to many things). But a monozygotic "identical" twin who happens to have schizophrenia is likely to have ventricles twice as large as the average healthy population while his or her healthy twin doesnt. These fluid spaces dont affect behavior directly, of course, but they indicate that there were abnormalities during the brains development.
So prefrontal functions seem to include abstract and creative thinking, fluency of thought and language, affective responses and the capacity for emotional attachments, social judgment, volition and drive, and selective attention. If obsessive-compulsive behavior is an exaggeration of frontal function, then the negative symptoms of schizophrenia might be considered a result of a low level of functioning up front.
BUT NONE OF THESE "localizations of function" is at all comparable to the relatively
predictable location of the hand in the middle of the motor strip. Especially when talking about
higher functions such as strategy, which require the integrated action of many parts of the brain,
one must be careful of speaking as if strategy were "located" in the prefrontal cortex, or that
narratives came from its bottom surface.|
If some function (say, planning a four-course meal) is particularly disruptable from a particular piece of cortex, that doesnt mean the function resides there. It may only mean that the function cannot survive loss of that particular piece of the larger circuit. Other parts of the brain may be equally involved in strategy, but their injury may not disrupt the function because another region can readily substitute for them. Injury (whether from bruising, strokes, and tumors or from gunshot and stab wounds) or temporary problems (such as epileptic seizures and migraine attacks) are only crude indicators of an areas function. This need to equivocate about localization of function is a source of enduring frustration to the neurophysiologist and neurologist.
Another reason for caution about localizing functions to particular places is that individuals are so variable. The anatomy is much more variable than textbooks tend to mention: For example, the primary visual cortex (that first big cortical-level map of the visual world in the back of the brain) varies threefold in size between seemingly normal adult humans. The motor strip isnt always in the same order, and patches of sensory cortex are sometimes found in front of motor strip, completely contrary to the motor-in-front, sensory-behind notions of the textbooks. If subdivisions as seemingly stereotyped as the "primary maps" can vary so much, we should be especially careful when generalizing about the brains terra incognita up front.
But such variability is also cause for suspecting that the frontal lobe may, in a given person, be much more specialized here and there than this general picture has indicated: The general picture pieced together by those natural-historianlike neurologists has emerged from hundreds of patients, each with a different lesion but each with perhaps a different organization. This jitter will blur the overall average organization; if we could map one individual and know all of his frontal-lobe areas in some detail, we might get the impression of considerable specialization, each little patch of cortex doing a somewhat different job. Neurosurgeons mapping the language cortex of individual patients have found much local specialization, though the overall map varies enormously from one patient to another. As neurosurgeons begin to operate on frontal-lobe tumor patients under local anesthesia in the same way as they routinely operate on temporal-lobe epileptics, and as functional brain imaging techniques improve, it is possible that a more detailed pattern of localization in frontal lobe will emerge as well.
HARVARD MED and its library were all very nice, but I also knew an expert on monkey frontal
lobe and its anatomical connections to the rest of the brain. My friend Terry Deacon can be
found over in Harvards anthropology department. Terry has been tracing the connections
of primate frontal lobe, seeing whom it talks to, and who talks to it. And its odd, Terry
says, but frontal lobes mappings to and from other regions have a marked similarity with
how the deep tectum (what animals without cerebral cortex tend to use instead for higher
functions) is organized: That midbrain structure, sitting atop the reticular formation, is what
most animals (even those with an extensive cerebral cortex) seem to use to orient to new things
in the environment. If my cat hears the can opener, you see her ears twist around to point that
way, her eyes turn in that direction, and then her head turns too. Thats exactly how
midbrain is organized, serving to orient the sense organs via simple motor programs. It
isnt a map of the body surface or of the visual field or of the muscles per se
its a "map" of orienting movements. Thats what frontal lobe may be duplicating
in a big way and then, of course, elaborating for even fancier versions of "What do I do
If you are searching for the center of everything, the seat of executive power in a brain, thats the kind of wiring that is needed for selective attention, focusing both sensation and movement. For people who believe in dualism of a sort, it suggests getting close to the seat of the soul, the place where the interface occurs between the immaterial and the material. I stick to the "physiologists premise" myself (it seems to be one of the occupational hazards of physiology), but one can understand why even a thoroughgoing atheist might wonder if some external agency wasnt occasionally at work. Consider this analysis of the sense of volition, by a leading sleep researcher:
Dreams are so strange and so involuntary as to challenge and deny the twin notions of rationality and responsibility. To be responsible, I must be rational; but in dreaming I appear irrational. And I lose my sense of volition. How, then, can I be responsible for my dreams? Surely they occur whether I will them or not. If I do not will them, then how can I cause them? And if not I, then who does will or cause them? While clearly involving me, dreams seem to happen regardless of my will; and they run their course with few exceptions no matter what I say, think, or feel.
AND SO THE INEVITABLE PRIMAL QUESTION: Where do I live, where do I control it all
from? And its corollary: Does something control me, or am I truly autonomous?|
If all this neural machinery is like a manufacturing plant presided over by executives, where does the President sit? If this is like a computer, where is the programmer? Deep in the frontal lobe? Surely to make a conscious machine, were going to have to understand this center of it all in order to construct a mimic.
Yet it isnt like a corporation, and it isnt like a computer; our consciousness is mechanically implemented by a process more analogous to an economy or political party, a distributed system without much central authority. There is no central place from which we consciously look out as a voyeur, from which a puppeteer pulls our strings. Yet starting sometime in the third year of life, there is a narrator for much of our conscious experience. One must understand what our narrator is, and in its own terms and phenomena (such as what happens in delirium and dreams), before one can appreciate how the lower-level machinery is voluntarily commanded when we finally "make up our minds" about a shopping trip or a career. Or, indeed, to glimpse a route to building a conscious robot.
But it is hard to see the narrator because of a thicket of man-made obstructions: all of those multiple meanings of a much-overused word, consciousness.
|The Cerebral Symphony (Bantam 1989) is my book on animal and human consciousness, using the setting of the Marine Biological Labs and Cape Cod.||AVAILABILITY is limited.