3 THE BRAIN AND THE CHARIOT
When shall we three meet again . . . ?
WM. SHAKESPEARE
Macbeth
THE BRAIN of a fish isn’t much. A fish has a notochord or spinal
cord, which it shares with even humbler invertebrates. A primitive
fish also has a little swelling at the front end of the spinal cord,
which is its brain. In higher fish the swelling is further developed
but still weighs no more than a gram or two. That swelling
corresponds in higher animals to the hindbrain or brainstem and the
midbrain.
The brain of modern fish are chiefly midbrain, with a tiny
forebrain; in modern amphibians and reptiles, it is the other way
around (see figure on page 55). And yet fossil endocasts of the
earliest known vertebrates show that the principal divisions of the
modern brain (hind-brain, midbrain and forebrain, for example) were
already established.
Five hundred million years ago, swimming in the
primeval seas, there were fishy creatures called ostracoderms and
placoderms, whose brains had recognizably the same major divisions
as ours. But the relative size and importance of these components,
and even their early functions, were certainly very different from
today. One of the most engaging views of the subsequent evolution of
the brain is a story of the successive accretion and specialization
of three further layers surmounting the spinal cord, hindbrain and
midbrain. After each evolutionary step, the older portions of the
brain still exist and must still be accommodated. But a new layer
with new functions has been added.
The principal contemporary exponent of this view is Paul MacLean,
chief of the Laboratory of Brain Evolution and Behavior of the
National Institute of Mental Health. One hallmark of MacLean’s work
is that it encompasses many different animals, ranging from lizards
to squirrel monkeys.
Another is that he and his colleagues have studied carefully the
social and other behavior of these animals to improve their
prospects of discovering what part of the brain controls what sort
of behavior.
Squirrel monkeys with “gothic” facial markings have a kind of ritual
or display which they perform when greeting one another. The males
bare their teeth, rattle the bars of their cage, utter a
high-pitched squeak, which is possibly terrifying to squirrel
monkeys, and lift their legs to exhibit an erect penis. While such
behavior would border on impoliteness at many contemporary human
social gatherings, it is a fairly elaborate act and serves to
maintain dominance hierarchies in squirrel-monkey communities.
MacLean has found that a lesion in one small part of a squirrel
monkey’s brain will prevent this display while leaving a wide range
of other behavior intact, including sexual and combative behavior.
The part that is involved is in the oldest part of the forebrain, a
part that humans as well as other primates share with out mammalian
and reptilian ancestors. In non-primate mammals and in reptiles,
comparable ritualized behavior seems to be controlled in the same
part of the brain, and lesions in this reptilian component can
impair other automatic types of behavior besides ritual-for example,
walking or running.
The connection between sexual display and position in a dominance
hierarchy can be found frequently among the primates. Among Japanese
macaques, social class is maintained and reinforced by daily
mounting: males of lower caste adopt the characteristic submissive
sexual posture of the female in oestrus and are briefly and
ceremonially mounted by higher-caste males. These mountings are both
common and perfunctory. They seem to have little sexual content but
rather serve as easily understood symbols of who is who in a complex
society.
In one study of the behavior of the squirrel monkey, Caspar, the
dominant animal in the colony and by far the most active
displayer, was never seen to copulate, although he accounted
for two-thirds of the genital display in the colony - most of it
directed toward other adult males. The fact that Caspar was
highly motivated to establish dominance but insignificantly
motivated toward sex suggests that while these two functions may
involve identical organ systems, they are quite separate. The
scientists studying this colony concluded:
“Genital display is
therefore considered the most effective social signal with respect
to group hierarchy. It is ritualized and seems to acquire the
meaning, ‘I am the master.’ It is most probably derived from sexual
activity, but it is used for social communication and separated from
reproductive activity. In other words, genital display is a ritual
derived from sexual behavior but serving social and not reproductive
purposes.”
In a television interview in 1976, a professional football player
was asked by the talk-show host if it was embarrassing for football
players to be together in the locker room with no clothes on. His
immediate response:
“We strut! No embarrassment at all. It’s as if
we’re saying to each other, ‘Let’s see what you got, man!’ - except
for a few, like the specialty team members and the water boy.”
The behavioral as well as neuroanatomical connections
between sex, aggression and dominance are borne out in a
variety of studies. The mating rituals of great cats and many
other animals are barely distinguishable, in their early stages,
from fighting. It is a commonplace that domestic cats
sometimes purr loudly and perversely while their claws are
slowly raking over upholstery or lightly clad human skin. The
use of sex to establish and maintain dominance is sometimes
evident in human heterosexual and homosexual practices
(although it is not, of course, the only element in such
practices), as well as in many “obscene” utterances.
Consider
the peculiar circumstance that the most common two-word
verbal aggression in English, and in many other languages,
refers to an act of surpassing physical pleasure; the English
form probably comes from a Germanic and Middle Dutch verb
fok-ken, meaning “to strike.” This otherwise puzzling usage can
be understood as a verbal equivalent of macaque symbolic
language, with the initial word “I” unstated but understood by
both parties. It and many similar expressions seem to be human
ceremonial mountings. As we will see, such behavior probably
extends much farther back than the monkeys, back through hundreds of
millions of years of geological time.
From experiments such as those with squirrel monkeys, MacLean has
developed a captivating model of brain structure and evolution that
he calls the triune brain. “We are obliged,” he says, “to look at
ourselves and the world through the eyes of three quite different
mentalities,” two of which lack the power of speech. The human
brain, MacLean holds,
“amounts to three interconnected biological
computers,” each with “its own special intelligence, its own
subjectivity, its own sense of time and space, its own memory,
motor, and other functions.”
Each brain corresponds to a separate
major evolutionary step. The three brains are said to be
distinguished neuroanatomically and functionally, and contain
strikingly different distributions of the neurochemicals dopamine
and cholinesterase.
At the most ancient part of the human brain lies the spinal cord;
the medulla and pons, which comprise the hindbrain; and the
midbrain. This combination of spinal cord, hindbrain and midbrain
MacLean calls the neural chassis. It contains the basic neural
machinery for reproduction and self-preservation, including
regulation of the heart, blood circulation and respiration. In a
fish or an amphibian it is almost all the brain there is. But a
reptile or higher animal deprived of its forebrain is, according to
MacLean, “as motionless and aimless as an idling vehicle without a
driver.”
Indeed, grand mal epilepsy can, I think, be described as a disease
in which the cognitive drivers are. all turned off because of a kind
of electrical storm in the brain, and the victim is left momentarily
with nothing operative but his neural chassis. This is a profound
impairment, temporarily regressing the victim back several hundreds
of millions of years. The ancient Greeks, whose name for the disease
we still use, recognized its profound character and called it the
disease inflicted by the gods.
MacLean has distinguished three sorts of drivers of the neural
chassis. The most ancient of them surrounds the midbrain (and
is made up mostly of what neuroanatomists call the olfactostriatum,
the corpus striatum, and the globus pallidus). We share it with the
other mammals and the reptiles. It probably evolved several hundred
million years ago. MacLean calls it the reptilian or R-complex.
Surrounding the R-complex is the limbic system, so called because it
borders on the underlying brain. (Our arms and legs are called limbs
because they are peripheral to the rest of the body.)
We share the
limbic system with the other mammals but not, in its full
elaboration, with the reptiles. It probably evolved more than one
hundred and fifty million years ago. Finally, surmounting the rest
of the brain, and clearly the most recent evolutionary accretion, is
the neocortex. Like the higher mammals and the other primates,
humans have a relatively massive neocortex. It becomes progressively
more developed in the more advanced mammals. The most elaborately
developed neocortex is ours (and the dolphins’ and whales’). It
probably evolved several tens of millions of years ago, but its
development accelerated greatly a few million years ago when humans
emerged.
A schematic representation of this picture of the human
brain is shown opposite, and a comparison of the limbic system with
the neocortex in three contemporary mammals is shown above. The
concept of the triune brain is in remarkable accord with the
conclusions, drawn independently from studies of brain-body mass
ratios in the previous chapter, that the emergence of mammals and of
primates (especially humans) was accompanied by major bursts in
brain evolution.
It is very difficult to evolve by altering the deep fabric of life;
any change there is likely to be lethal. But fundamental change can
be accomplished by the addition of new systems on top of old ones.
This is reminiscent of a doctrine which was called recapitulation by
Ernst Haeckel, a nineteenth-century German anatomist, and which has
gone through various cycles of scholarly acceptance and rejection.
Haeckel held that in its embryological development, an animal tends
to repeat or recapitulate the sequence that its ancestors followed
during their evolution. And indeed in human intrauterine development
we run through stages very much like fish, reptiles and
nonprimate
mammals before we become recognizably human.
The fish stage even has gill slits, which are absolutely useless for
the embryo who is nourished via the umbilical cord, but a necessity
for human embryology: since gills were vital to our ancestors, we
run through a gill stage in becoming human. The brain of a human
fetus also develops from the inside out, and, roughly speaking, runs
through the sequence: neural chassis, R-complex, limbic system and
neocortex.
The reason for recapitulation may be understood as follows:
Natural selection operates only on individuals, not on species and
not very much on eggs or fetuses. Thus the latest evolutionary
change appears postpartum. The fetus may have characteristics, like
the gill slits in mammals, that are entirely maladaptive after
birth, but as long as they cause no serious problems for the fetus
and are lost before birth, they can be retained. Our gill slits are
vestiges not of ancient fish but of ancient fish embryos.
Many new
organ systems develop not by the addition and preservation but by
the modification of older systems, as, for example, the modification
of fins to legs, and legs to flippers or wings; or feet to hands to
feet; or sebaceous glands to mammary glands; or gill arches to ear
bones; or shark scales to shark teeth. Thus evolution by addition
and the functional preservation of the preexisting structure must
occur for one of two reasons-either the old function is required as
well as the new one, or there is no way of bypassing the old system
that is consistent with survival.
There are many other examples in nature of this sort of
evolutionary development. To take an almost random case,
consider why plants are green. Green-plant photosynthesis
utilizes light in the red and the violet parts of the solar
spectrum to break down water, build up carbohydrates and do
other planty things. But the sun gives off more light in the
yellow and the green part of the spectrum than in the red or
violet.
Plants with chlorophyll as their only photosynthetic
pigment are rejecting light where it is most plentiful. Many
plants seem belatedly to have “noticed” this and have made
appropriate adaptations. Other pigments, which reflect red light
and absorb yellow and green light, such as carotenoids and
phycobilins, have evolved. Well and good. But have those plants
with new photo-synthetic pigments abandoned chlorophyll? They have
not.
The figure on page 61 shows the photosynthetic factory of a red
alga. The striations contain the chlorophyll, and the little spheres
nestling against these striations contain the phycobilins, which
make a red alga red. Conservatively, these plants pass along the
energy they acquire from green and yellow sunlight to the
chlorophyll pigment that, even though it has not absorbed the light,
is still instrumental in bridging the gap between light and
chemistry in all plant photosynthesis.
Nature could not rip out the
chlorophyll and replace it with better pigments; the chlorophyll is
woven too deeply into the fabric of life. Plants with accessory
pigments are surely different. They are more efficient. But there,
still working, although with diminished responsibilities, at the
core of the photosynthetic process is chlorophyll.
The evolution of
the brain has, I think, proceeded analogously. The deep and ancient
parts are functioning still.
1 - THE R-COMPLEX
If the preceding view is correct, we should expect the R-complex in
the human brain to be in some sense performing dinosaur functions
still; and the limbic cortex to be thinking the thoughts of pumas
and ground sloths. Without a doubt, each new step in brain evolution
is accompanied by changes in the physiology of the preexisting
components of the brain. The evolution of the R-complex must have
seen changes in the midbrain, and so on. What is more, we know that
the control of many functions is shared in different components of
the brain. But at the same time it would be astonishing if the brain
components beneath the neocortex were not to a significant extent
still performing as they did in our remote ancestors.
MacLean has shown that the R-complex plays an important role
in aggressive behavior, territoriality, ritual and the
establishment of social hierarchies. Despite occasional welcome
exceptions, this seems to me to characterize a great deal of
modern human bureaucratic and political behavior. I do not
mean that the neocortex is not functioning at all in an American
political convention or a meeting of the Supreme Soviet; after
all, a great deal of the communication at such rituals is verbal
and therefore neocortical. But it is striking how much of our actual
behavior -as distinguished from what we say and think about it- can
be described in reptilian terms. We speak commonly of a
“cold-blooded” killer. Machiavelli’s advice to his Prince was
“knowingly to adopt the beast.”
In an interesting partial anticipation of these ideas, the American
philosopher Susanne Langer wrote:
“Human life is shot through and
through with ritual, as it is also with animalian practices. It is
an intricate fabric of reason and rite, of knowledge and religion,
prose and poetry, fact and dream.... Ritual, like art, is
essentially the active termination of a symbolic transformation of
experience. It is born in the cortex, not in the ‘old brain’; but it
is born of an elementary need of that organ, once the organ has
grown to human estate.”
Except for the fact that the R-complex is in
the “old brain,” this seems to be right on target.
I want to be very clear about the social implications of the
contention that reptilian brains influence human actions. If
bureaucratic behavior is controlled at its core by the R-complex,
does this mean there is no hope for the human future? In human
beings, the neo-cortex represents about 85 percent of the brain,
which is surely some index of its importance compared to the
brainstem, R-complex and limbic system. Neuro-anatomy, political
history, and introspection all offer evidence that human beings are
quite capable of resisting the urge to surrender to every impulse of
the reptilian brain.
There is no way, for example, in which the
Bill of Rights of the
U.S. Constitution could have been recorded, much less
conceived, by the R-complex. It is precisely our plasticity, our
long childhood, that prevents a slavish adherence to genetically
preprogrammed behavior in human beings more than in any
other species. But if the triune brain is an accurate model of
how human beings function, it does no good whatever to ignore
the reptilian component of human nature, particularly our
ritualistic and hierarchical behavior.
On the contrary, the model
may help us to understand what human beings are about.
(I
wonder, for example, whether the ritual aspects of many
psychotic illnesses-e. g., hebephrenic schizophrenia-could be
the result of hyperactivity of some center in the R-complex, or of a
failure of some neocortical site whose function is to repress or
override the R-complex. I also wonder whether the frequent
ritualistic behavior in young children is a consequence of the
still-incomplete development of their neocortices.)
In a curiously apt passage, G. K. Chesterton wrote:
“You can free
things from alien or accidental laws, but not from the laws of their
own nature. . . . Do not go about . . . encouraging triangles to
break out of the prison of their three sides. If a triangle breaks
out of its three sides, its life comes to a lamentable end.”
But not
all triangles are equilateral. Some substantial adjustment of the
relative role of each component of the triune brain is well within
our powers.
2 - THE LIMBIC SYSTEM
The limbic system appears to generate strong or particularly
vivid
emotions. This immediately suggests an additional perspective on
the
reptilian mind: it is not characterized by powerful passions and
wrenching contradictions but rather by a dutiful and stolid
acquiescence to whatever behavior its genes and brains dictate.
Electrical discharges in the limbic system sometimes result in
symptoms similar to those of psychoses or those produced by
psychedelic or hallucinogenic drugs. In fact, the sites of action of
many psychotropic drugs are in the limbic system. Perhaps it
controls exhilaration and awe and a variety of subtle emotions that
we sometimes think of as uniquely human.
The “master gland,” the pituitary, which influences other glands and
dominates the human endocrine system, is an intimate part of the
limbic region. The mood-altering qualities of endocrine imbalances
give us an important hint about the connection of the limbic system
with states of mind. There is a small almond-shaped inclusion in the
limbic system called the amygdala which is deeply involved in both
aggression and fear.
Electrical stimulation of the amygdala in placid domestic
animals can rouse them to almost unbelievable states of fear or
frenzy. In one case, a house cat cowered in terror when presented
with a small white mouse. On the other hand, naturally ferocious
animals, such as the lynx, become docile and tolerate being petted
and handled when their amygdalas are extirpated. Malfunctions in the
limbic system can produce rage, fear or sentimentality that have no
apparent cause.
Natural hyperstimulation may produce the same
results: those suffering from such a malady find their feelings
inexplicable and inappropriate; they may be considered mad.
At least some of the emotion-determining role of such limbic
endocrine systems as the pituitary amygdala, and hypothalamus is
provided by small hormonal proteins which they exude, and which
affect other areas of the brain. Perhaps the best-known is the
pituitary protein, ACTH (adrenocorticotropic hormone), which can
affect such diverse mental functions as visual retention, anxiety
and attention span.
Some small hypothalamic proteins have been
identified tentatively in the third ventricle of the brain, which
connects the hypothalamus with the thalamus, a region also within
the limbic system. The stunning pictures on page 65, taken with an
electron microscope, show two close-ups of action in the third
ventricle. The diagram on page 73 may help clarify some of the brain
anatomy just described.
There are reasons to think that the beginnings of altruistic
behavior are in the limbic system. Indeed, with rare exceptions
(chiefly the social insects), mammals and birds are the only
organisms to devote substantial attention to the care of their
young-an evolutionary development that, through the long
period of plasticity which it permits, takes advantage of the
large information-processing capability of the mammalian and
primate brains. Love seems to be an invention of the
mammals.*
*
This rule on the relative parental concern of mammals and reptiles
is, however, by no means without exceptions. Nile crocodile mothers
carefully put their fresh hatchlings in their mouths and carry them
to the comparative safety of the river waters; while Serengeti male
lions will, upon newly dominating
a pride, destroy all the resident cubs. But on the whole, mammals
show a strikingly greater degree of parental care than do reptiles.
The distinction may have been even more striking one hundred million
years ago.
Much in animal behavior substantiates the notion that strong
emotions evolved chiefly in mammals and to a lesser extent in birds.
The attachment of domestic animals to humans is, I think, beyond
question. The apparently sorrowful behavior of many mammalian
mothers when their young are removed is well-known. One wonders just
how far such emotions go. Do horses on occasion have glimmerings of
patriotic fervor? Do dogs feel for humans something akin to
religious ecstasy? What other strong or subtle emotions are felt by
animals that do not communicate with us?
The oldest part of the limbic system is the olfactory cortex, which
is related to smell, the haunting emotional quality of which is
familiar to most humans. A major component of our ability to
remember and recall is localized in the hippocampus, a structure
within the limbic system. The connection is clearly shown by the
profound memory impairment that results from lesions of the
hippocampus. In one famous case, H. M., a patient with a long
history of seizures and convulsions, was subjected to a bilateral
extirpation of the entire region about the hippocampus in a
successful attempt to reduce their frequency and severity. He
immediately became amnesic. He retained good perceptual skills, was
able to learn new motor skills and experienced some perceptual
learning but essentially forgot everything more than a few hours
old.
His own comment was “Every day is alone in itself-whatever
enjoyment I’ve had and whatever sorrow I’ve had.” He described his
life as a continuous extension of the feeling of disorientation many
of us have upon awakening from a dream, when we have great
difficulty remembering what has just happened. Remarkably enough,
despite this severe impairment, his IQ improved after his hippocampectomy. He apparently could detect smells but had
difficulty identifying by name the source of the smell. He also
exhibited an apparent total disinterest in sexual activity.
In another case, a young American airman was injured in a mock duel
with another serviceman, when a miniature fencing foil was plunged
into his right nostril, puncturing a small part of the limbic system
immediately above. This resulted in a severe impairment of memory,
similar to but not so severe as H. M.’s; a wide range of his
perceptual and intellectual abilities was unaffected. His memory
impairment was particularly noticeable with verbal material. In
addition, the accident seems to have rendered him both impotent and
unresponsive to pain. He once walked barefoot on the sun-heated
metal deck of a cruise ship, without realizing that his feet were
being badly burned until his fellow passengers complained of the
uncomfortable odor of charring flesh. On his own, he was aware of
neither the pain nor the smell.
From such cases, it seems apparent that so complex a mammalian
activity as sex is controlled simultaneously by all three components
of the triune brain - the R-complex, the limbic system and the
neocortex. (We have already mentioned the involvement of the
R-complex and the limbic system in sexual activity. Evidence for
involvement of the neocortex can be easily obtained by
introspection.)
One segment of the old limbic system is devoted to oral and
gustatory functions; another, to sexual functions. The connection of
sex with smell is very ancient, and is highly developed in insects-a
circumstance that offers insight into both the importance and the
disadvantages of reliance on smell in our remote ancestors.
I once witnessed an experiment in which the head of a green
bottle fly was connected by a very thin wire to an oscilloscope
that displayed, in a kind of graph, any electrical impulses
produced by the fly’s olfactory system. (The fly’s head had only
recently been severed from its body-in order to gain access to
the olfactory apparatus-and was still in many respects
functional.*)
* The heads and bodies of anthropods can briefly function without
each other very nicely. A female praying mantis will often respond
to earnest courting by decapitating her suitor. While this would be
viewed as unsociable among humans, it is not so among insects:
extirpation of the brain removes sexual inhibitions and encourages
what is left of the male to mate. Afterwards, the female completes
her celebratory repast, dining, of course, alone. Perhaps this
represents a cautionary lesson against excessive sexual repression.
Such olfactory specialization is quite common in insects. The male
silkworm moth is able to detect the female’s sex attractant molecule
if only about forty molecules per second reach its feathery
antennae. A single female silkworm moth need release only a
hundredth of a microgram of sex attractant per second to attract
every male silkworm in a volume of about a cubic mile. That is why
there are silkworms.
The experimenters wafted a wide variety of odors
in front of it, including obnoxious and irritating gases such as
ammonia, with no discernible effects. The line traced out on the
oscilloscope screen was absolutely flat and horizontal. Then a
tiny quantity of the sex attractant released by the female of the
species was waved before the severed head, and an enormous vertical
spike obligingly appeared on the oscilloscope screen. The bottle fly
could smell almost nothing except the female sex attractant. But
that molecule he could smell exceedingly well.
Perhaps the most curious exploitation of the reliance on smell
to find a mate and continue the species is found in a South
African beetle, which burrows into the ground during the
winter. In the spring, as the ground thaws, the beetles emerge,
but the male beetles groggily disinter themselves a few weeks
before the females do. In this same region of South Africa, a
species of orchid has evolved which gives off an aroma
identical to the sex attractant of the female beetle. In fact,
orchid and beetle evolution have produced essentially the same
molecule.
The male beetles turn out to be exceedingly
nearsighted; and the orchids have evolved a configuration of
their petals that, to a myopic beetle, resembles the female in a
receptive sexual posture. The male beetles enjoy several
weeks of orgiastic ecstasy among the orchids, and when
eventually the females emerge from the ground, we can
imagine a great deal of wounded pride and righteous
indignation. Meanwhile the orchids have been successfully
cross-pollinated by the amorous male beetles, who, now properly
abashed, do their best to continue the beetle species; and both
organisms survive. (Incidentally, it is in the interest of the
orchids not to be too consummately attractive; if the beetles fail
to reproduce themselves, the orchids are in trouble.)
We thus
discover one limitation to purely olfactory sexual stimuli. Another
is that since every female beetle produces the same sex attractant,
it is not easy for a male beetle to fall in love with the lady
insect of his heart’s desire. While male insects may display
themselves to attract a female, or-as with stag beetles-engage in
mandible-to-mandible combat with the female as the prize, the
central role of the female sex attractant in mating seems to reduce
the extent of sexual selection among the insects.
Other methods of finding a mate have been developed in reptiles,
birds and mammals. But the connection of sex with smell is still
apparent neuro-anatomically in higher animals as well as anecdotally
in human experience. I sometimes wonder if deodorants, particularly
“feminine” deodorants, are an attempt to disguise sexual stimuli and
keep our minds on something else.
3 - THE NEOCORTEX
Even in fish, lesions of the forebrain destroy the traits of
initiative and caution. In higher animals these traits, much
elaborated, seem localized in the neo-cortex, the site of many
of the characteristic human cognitive functions. It is frequently
discussed in terms of four major regions or lobes: the frontal,
parietal, temporal and occipital lobes. Early neurophysiologists
held that the neocortex was primarily connected only to other
places in the neocortex, but it is now Known that there are
many neural connections with the sub-cortical brain. It is,
however, by no means clear that the neocortical subdivisions
are actually functional units.
Each certainly has many quite
different functions, and some functions may be shared among
or between lobes. Among other functions, the frontal lobes
seem to be connected with deliberation and the regulation of
action; the parietal lobes, with spatial perception and the exchange
of information between the brain and the rest of the body; the
temporal lobes, with a variety of complex perceptual tasks; and the
occipital lobes, with vision, the dominant sense in humans and other
primates.
For many decades the prevailing view of neurophysiologists was that
the frontal lobes, behind the forehead, are the sites of
anticipation and planning for the future, both characteristically
human functions. But more recent work has shown that the situation
is not so simple. A large number of cases of frontal lesions-largely
suffered in warfare and as gunshot wounds-have been investigated by
the American neurophysiologist Hans-Lukas Teuber of the
Massachusetts Institute of Technology.
He found that many
frontal-lobe lesions have almost no obvious effects on behavior;
however, in severe pathology of the frontal lobes,
“the patient is
not altogether devoid of capacity to anticipate a course of events,
but cannot picture himself in relation to those events as a
potential agent.”
Teuber emphasized the fact that the frontal lobe
may be involved in motor as well as cognitive anticipation,
particularly in estimating what the effect of voluntary movements
will be. The frontal lobes also seem to be implicated in the
connection between vision and erect bipedal posture.
Thus the frontal lobes may be involved with peculiarly human
functions in two different ways. If they control anticipation of
the future, they must also be the sites of concern, the locales of
worry. This is why transection of the frontal lobes reduces
anxiety. But prefrontal lobotomy must also greatly reduce the
patient’s capacity to be human. The price we pay for
anticipation of the future is anxiety about it. Foretelling disaster
is probably not much fun; Pollyanna was much happier than
Cassandra.
But the Cassandric components of our nature are
necessary for survival. The doctrines for regulating the future
that they produced are the origins of ethics, magic, science and
legal codes. The benefit of foreseeing catastrophe is the ability
to take steps to avoid it, sacrificing short-term for long-term
benefits. A society that is, as a result of such foresight,
materially secure generates the leisure time necessary for social
and technological innovation.
The other suspected function of the frontal lobes is to make
possible mankind’s bipedal posture. Our upright stance may not have
been possible before the development of the frontal lobes. As we
shall see later in more detail, standing on our own two feet freed
our hands for manipulation, which then led to a major accretion of
human cultural and physiological traits. In a very real sense,
civilization may be a product of the frontal lobes.
Visual information from the eyes arrives in the human brain chiefly
in the occipital lobe, in the back of the head; auditory
impressions, in the upper part of the temporal lobe, beneath the
temple. There is fragmentary evidence that these components of the
neo-cortex are substantially less well developed in blind
deaf-mutes. Lesions in the occipital lobe-as produced by gunshot
wounds, for example - frequently induce an impairment in the field of
vision. The victim may be in all other respects normal but able to
see only with peripheral vision, perceiving a solid, dark blot
looming in front of him at the center of the normal field of view.
In other cases, more bizarre perceptions follow, including
geometrically regular, cursive floating impairments in the visual
field, and “visual fits” in which (for example) objects on the floor
to the patient’s lower right are momentarily perceived as floating
in the air to his upper left and rotated 180 degrees through space.
It may even be possible to map which parts of the occipital lobes
are responsible for which visual functions by systematically
calculating the impairments of vision from various occipital
lesions. Permanent impairments of vision are much less likely to
occur in the very young, whose brains seem able to repair themselves
or transfer functions to neighboring regions very well.
The ability to connect auditory with visual stimuli is also
localized in the temporal lobe. Lesions in the temporal lobe can
result in a form of aphasia, the inability to recognize spoken
words. It is remarkable and significant that brain-damaged
patients can be completely competent in spoken language and
entirely incompetent in written language, or vice versa. They may be
able to write but unable to read; able to read numbers but not
letters; able to name objects but not colors. There is in the
neocortex a striking separation of function, which is contrary to
such common-sense notions as that reading and writing, or
recognizing words and numbers, are very similar activities.
There
are also as yet unconfirmed reports of brain damage that results
only in the inability to understand the passive voice or
prepositional phrases or possessive constructions. (Perhaps the
locale of the subjunctive mood will one day be found. Will Latins
turn out to be extravagantly endowed and English-speaking peoples
significantly short-changed in this minor piece of brain anatomy?)
Various abstractions, including the “parts of speech” in grammar,
seem, astonishingly, to be wired into specific regions of the brain.
In one case, a temporal-lobe lesion resulted in a surprising
impairment in the patient’s perception of faces, even the faces of
his immediate family. Presented with the face on this page, he
described it as “possibly” being an apple. Asked to justify this
interpretation, he identified the mouth as a cut in the apple, the
nose as the stem of the apple folded back on its surface, and the
eyes as two worm holes. The same patient was perfectly able to
recognize sketches of houses and other inanimate objects. A wide
range of experiments shows that lesions in the right temporal lobe
produce amnesia for certain types of nonverbal material, while
lesions in the left temporal lobe produce a characteristic loss of
memory for language.
Our ability to read and make maps, to orient ourselves spatially in
three dimensions and to use the appropriate symbols-all of which are
probably involved in the development if not the use of language -are
severely impaired by lesions in the parietal lobes, near the top of
the head. One soldier who suffered a massive wartime penetration of
the parietal lobe was for a full year unable to orient his feet into
his slippers, much less find his bed in the hospital ward. He
nevertheless eventually experienced an almost complete recovery.
A lesion of the angular gyrus of the neocortex, in the parietal
lobe, results in alexia, the inability to recognize the printed
word. The parietal lobe appears to be involved in all human symbolic
language and, of all the brain lesions, a lesion in the parietal
lobe causes the greatest decline in intelligence as measured by
activities in everyday life.
Chief among the neocortical abstractions are the human symbolic
languages, particularly reading and writing and mathematics. These
seem to require cooperative activities of the temporal, parietal and
frontal lobes, and perhaps the occipital as well. Not all symbolic
languages are neocortical however; bees- without a hint of a
neocortex- have an elaborate dance language, first elucidated by the
Austrian entomologist Karl von Frisch, by which they communicate
information on the distance and direction of available food. It is
an exaggerated gestural language, imitative of the motions bees in
fact perform when finding food-as if we were to make a few steps
towards the refrigerator, point and rub our bellies, with our
tongues lolling out all the while.
But the vocabularies of such
languages are extremely limited, perhaps only a few dozen words. The
kind of learning that human youngsters experience during their long
childhood seems almost exclusively a neocortical function.
While most olfactory processing is in the limbic system, some occurs
in the neocortex. The same division of function seems to apply to
memory. A principal part of the limbic system, other than the
olfactory cortex, is, as we have mentioned, the hippocampal cortex.
When the olfactory cortex is excised, animals can still smell,
although with a much lower efficiency. This is another demonstration
of the redundancy of brain function.
There is some evidence that, in
contemporary humans, the short-term memory of smell resides in the
hippocampus. The original function of the hippocampus may have been
exclusively the short-term memory of smell, useful in, for example,
tracking prey or finding the opposite sex. But a bilateral hippocampal lesion in humans results, as in the case of H. M., in
a profound impairment of all varieties of short-term memory.
Patients with such lesions literally cannot remember from one moment
to the next. Clearly, both hippocampus and frontal lobes are
involved in human short-term memory.
One of the many interesting implications of this is that short-term
and long-term memory reside mostly in different parts of the brain.
Classical conditioning- the ability of Pavlov’s dogs to salivate
when the bells rang-seems to be located in the limbic system. This
is long-term memory, but of a very restricted kind. The
sophisticated sort of human long-term memory is situated in the neocortex, which is consistent with the human ability to think
ahead.
As we grow old, we sometimes forget what has just been said
to us while retaining vivid and accurate recollections of events in
our childhood. In such cases, little seems to be wrong with either
our short-term or our long-term memories; the problem is the
connection between the two-we have great difficulty in accessing new
material into the long-term memory. Penfield believed that this lost
accessing ability arises from an inadequate blood supply to the
hippocampus in old age-because of arteriosclerosis or other physical
disabilities. Thus elderly people-and ones not so elderly-may have
serious impairments in accessing short-term memory while being
otherwise perfectly alert and intellectually keen.*
*
Indeed, there is a range of medical evidence on the connection
between blood supply and intellectual abilities. It has long been
known that patients deprived of oxygen for some minutes can
experience permanent and serious mental impairment. Operations to
remove material from clogged carotid arteries in an effort to
prevent stroke yield unexpected benefits. According to one study,
six weeks after such operations, the patients showed an average
increase in IQ of eighteen points, a substantial improvement. And
there has been some speculation that immersion in hyperbaric
oxygen-that is, oxygen under high pressure-can raise the
intelligence of infants.
This phenomenon
also shows a clear-cut distinction between short-term and long-term
memory, consistent with their localization in different parts of the
brain. Waitresses in short-order restaurants can remember an
impressive amount of information, which they accurately transmit to
the kitchen. But an hour later, the information has vanished
utterly. It was put into the short-term memory only, and no effort
was made to access it into the long-term memory.
The mechanics of recall can be complex. A common experience is that
we know something is in our long-term memory - a word, a name, a face,
an experience - but find ourselves unable to call it up. No matter how
hard we try, the memory resists retrieval. But if we think sideways
at it, recalling some slightly related or peripheral item, it often
follows unbidden. (Human vision is also a little like this. When we
look directly at a faint object-a star, say-we are using the fovea,
the part of the retina with the greatest acuity and the greatest
density of cells called cones.
But when we avert our vision slightly-when, in a manner of
speaking, we look sideways at the object-we bring into play the
cells called rods, which are sensitive to feeble illumination and
so able to perceive the faint star.) It would be interesting to know
why thinking sideways improves memory retrieval; it may be merely
associating to the memory trace by a different neural pathway. But
it does not suggest particularly efficient brain engineering.
We have all had the experience of awakening with a particularly
vivid, chilling, insightful or otherwise memorable dream clearly in
mind; saying to ourselves, “I’ll certainly remember this dream in
the morning”; and the next day having not the foggiest notion about
the content of the dream or, at best, a vague trace of an emotion
tone. On the other hand, if I am sufficiently exercised about the
dream to awaken my wife in the middle of the night and tell her
about it, I have no difficulty remembering its contents unaided in
the morning.
Likewise, if I take the trouble of writing the dream
down, when I awaken the next morning I can remember the dream
perfectly well without referring to my notes. The same thing is true
of, for example, remembering a telephone number. If I am told a
number and merely think about it, I am likely to forget it or
transpose some of the digits. If I repeat the numbers out loud or
write them down, I can remember them quite well. This surely means
that there is a part of our brain which remembers sounds and images,
but not thoughts.
I wonder if that sort of memory arose before we
had very many thoughts-when it was important to remember the hiss of
an attacking reptile or the shadow of a plummeting hawk, but not our
own occasional philosophical reflections.
ON HUMAN NATURE
Despite the intriguing localization of function in
the triune brain
model, it is, I stress again, an oversimplification to insist upon
perfect separation of function. Human ritual and emotional behavior
are certainly influenced strongly by neocortical abstract reasoning;
analytical demonstrations of the validity of purely religious
beliefs have been proffered, and there are philosophical
justifications for hierarchical behavior, such as Thomas Hobbes’
“demonstration” of the divine right of kings. Likewise, animals that
are not human - and in fact even some animals that are not
primates - seem to show glimmerings of analytical abilities. I
certainly have such an impression about dolphins, as I described in
my book The Cosmic Connection.
Nevertheless, while bearing these caveats in mind, it seems a useful
first approximation to consider the ritualistic and hierarchical
aspects of our lives to be influenced strongly by the R-complex and
shared with our reptilian forebears; the altruistic, emotional and
religious aspects of our lives to be localized to a significant
extent in the limbic system and shared with our nonprimate mammalian
forebears (and perhaps the birds); and reason to be a function of
the neo-cortex, shared to some extent with the higher primates and
such cetaceans as dolphins and whales.
While ritual, emotion and
reasoning are all significant aspects of human nature, the most
nearly unique human characteristic is the ability to associate
abstractly and to reason. Curiosity and the urge to solve problems
are the emotional hallmarks of our species; and the most
characteristically human activities are mathematics, science,
technology, music and the arts - a somewhat broader range of subjects
than is usually included under the “humanities.” Indeed, in its
common usage this very word seems to reflect a peculiar narrowness
of vision about what is human. Mathematics is as much a “humanity”
as poetry. Whales and elephants may be as “humane” as humans.
The triune-brain model derives from studies of comparative
neuroanatomy and behavior. But honest introspection is not
unknown in the human species, and if the triune-brain model is
correct, we would expect some hint of it in the history of human
self-knowledge. The most widely known hypothesis that is at least
reminiscent of the triune brain is Sigmund Freud’s division of the
human psyche into id, ego and superego. The aggressive and sexual
aspects of the R-complex correspond satisfyingly to the Freudian
description of the id (Latin for “it”-i.e., the beast-like aspect
of our natures); but, so far as I know, Freud did not in his
description of the id lay great stress on the ritual or
social-hierarchy aspects of the R-complex.
He did describe emotions
as an ego function-in particular the “oceanic experience,” which is
the Freudian equivalent of the religious epiphany. However, the
superego is not depicted primarily as the site of abstract reasoning
but rather as the internalizer of societal and parental strictures,
which in the triune brain we might suspect to be more a function of
the R-complex. Thus I would have to describe the psychoanalytic
tripartite mind as only weakly in accord with the triune-brain
model.
Perhaps a better metaphor is Freud’s division of the mind into the
conscious; the preconscious, which is latent but capable of being
tapped; and the unconscious, which is repressed or otherwise
unavailable. It was the tension that exists among the components of
the psyche that Freud had in mind when he said of man that “his
capacity for neurosis would merely be the obverse of his capacity
for cultural development.” He called the unconscious functions
“primary processes.”
A superior agreement is found in the metaphor for the human psyche
in the Platonic dialogue Phaedrus. Socrates likens the human soul to
a chariot drawn by two horses-one black, one white-pulling in
different directions and weakly controlled by a charioteer. The
metaphor of the chariot itself is remarkably similar to MacLean’s
neural chassis; the two horses, to the R-complex and the
limbic
cortex; and the charioteer barely in control of the careening
chariot and horses, to the neocortex.
In yet another metaphor, Freud described the ego as the rider
of an unruly horse. Both the Freudian and the Platonic
metaphors emphasize the considerable independence of and
tension among the constituent parts of the psyche, a point that
characterizes the human condition and to which we will return.
Because of the neuroanatomical connections between the three
components, the triune brain must itself, like the Phaedrus chariot,
be a metaphor; but it may prove to be a metaphor of great utility
and depth.
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