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Albert Einstein died in his sleep in 1955. As he had requested, his body was
cremated and the ashes scattered. Before cremation, however, his brain was
removed by a pathologist named Thomas S. Harvey, who wanted to inspect
Einstein's brain for evidence of what made it so different. At that time,
nothing remarkable was found. Recently, when Einstein’s brain was examined on
a more molecular level, previously undetected areas of remarkable development
indeed were found in the cortex.
We are all unmistakably different; even identical twins develop their
own personalities and preferences. Yet the organ we contain within us, that we
appoint as the instigator of our individualities, of our abilities, of our
selfhood and of our private thoughts, differs very little in its gross
characteristics among healthy people. Regardless of personal traits, human
brains share the same number of lobes encasing more primitive parts within and
connected by roughly the same number of neurons, or cells. The brain and spinal
cord are collectively known as the central nervous system. Once development of
the central nervous system is completed, in early childhood, no new neurons are
formed; when neurons die, they are not replaced.
Brain cells consist, very generally, of a cell body and processes at either
end by which to receive and transmit information. From one end of the cell body
sprout dendrites, which bring messages in; opposite the dendrites, the cell body
extends into an axon, which transmits impulses along its length until reaching
the end, called the "terminal bouton," or button. Impulses reaching
the terminal bouton cause calcium channels to open and admit calcium, which
stimulates vesicles within the bouton to release a transmitter substance that,
if released in sufficient quantity, will be received by dendrites of a
neighboring neuron and continue transmission of the message. The gaps between
axons of one cell and dendrites of the next are called synapses.
Thus, healthy brains contain the same neuronal construction.
Among such
brains, however, there is one discernible distinction: Differences in the number
of connections among neurons. The number of connections among neurons is
determined by the quantity, at one end, of dendritic "sprouts" and, at
the other, by terminal boutons. In fact, dendrites, like trees, are said to
arborize. When rats in a litter are divided into two groups, one of which is
presented with a "boring" environment devoid of playthings and
playmates while the other receives an "enriched" environment full of
challenges and camaraderie, brains of rats from the impoverished environment are
poor in dendritic development, while brains of their stimulated littermates are
rich in arborization. What stimulates a neuron to further arborization is use;
what allows a connection to whither away is non-use.
So, like muscles, the brain benefits from exercise. But just as improper
movement can injure our muscles, there is evidence that unseemly connections
among neurons can be strengthened by use--in a palpable way, we are the
creations of our thoughts and beliefs.
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A healthy and good-looking 49-year-old man with a shock of salt-and-pepper
hair entered the neurologist's office. The man was cheerful and friendly. When
the doctor asked him his name and birth date, and the name of the town in
Connecticut in which he was born, the man answered genially and in detail.
Prompted by the doctor, he recollected the houses in which he and his family had
lived, and of his early knack for mathematics. He was particularly enthusiastic
about his time in the navy, when he was 17 and just out of high school. It was a
time of excitement and novelty for him.
But something about the freshness of those memories seemed
amiss to the
doctor. The man had been in the navy some 20 years before, and yet he spoke
almost as though that time was not yet ended. The doctor asked the man his age.
The man hesitated for a moment, as though calculating. Then he said he was 19.
When the doctor held a mirror up to the man's face, the man paled.
The story of Mr. G. is written by the neurologist Oliver Sacks.
Intelligence testing showed Mr. G. to have excellent ability. He was
observant, witty, and logical, and could solve complex puzzles--unless the
process took too long. If Dr. Sacks were to cover up such items as a pair
of eyeglasses, a box of matches, and a comb on the table in front of
Mr. G., the patient could recollect what lay beneath the cover for only a
few seconds' time. If prevented from rehearsing, Mr. G. would forget in a
minute what the cover concealed; he would even forget that he had been asked to
remember what lay there.
The patient's profound loss of recent memory was diagnosed as Korsakov's
syndrome. In 1889 Sergei Korsakoff, a Russian doctor, identified the severe
memory impairment, a result of alcoholic destruction of a minute part of the
brain that is crucial to memory. The primary symptom of Korsakov's syndrome is
anterograde amnesia, with which a person can remember old memories but is unable
to form new ones. Although those with the syndrome can converse normally, in a
few minutes the conversation will be forgotten. One researcher quoted a patient
thus:
Every day is alone in itself, whatever enjoyment I've had, and whatever
sorrow I've had.... At this moment everything looks clear to
me, but what happened just before? That's what worries me. It's like waking
from a dream; I don't remember.
Korsakov's syndrome is associated with severe alcoholics.
Because alcohol has
a lot of calories, many alcoholics avoid food and consequently their bodies
become low in nutrients. Alcohol also appears to inhibit absorption of thiamin
(vitamin B1) from the intestine. If the deficiency is of sufficient
duration and amount, the brain is damaged. There is some controversy over just
where the damage occurs. Many patients autopsied with Korsakov's syndrome show
destruction of the mammillary bodies, structures that form part of a neural
circuit (which also includes the hippocampus, with which you will be acquainted
later) believed to function in the deposition of memories. However, autopsies of
severe alcoholics sometimes reveal damage to structures along that circuit,
apparently without discernible effect on memory.
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Another often-found site of damage is a certain small section of the
thalamus. The severe retrograde amnesia manifested by Mr. G. is rare, even
among habitual alcoholics. When it occurs, it profoundly impresses upon us the
contribution of memory to our functioning as sentient beings.
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Think for a moment about this achievement, which most of us take for
granted. Most of us cannot state the rules of our native tongue, but instantly
we recognize statements that violate the rules of grammaticality. We have
unconscious but ironclad competence. You can reinstate or recall, but you can't
re-fall down. You might forget the exact words to the tune, but you won't be
fooled into accepting, "The old lady little from Pasadena."
Why not?
Language links sounds to meaning. Often the meaning is something concrete,
such as nouns; often it is something abstract, such as infinity, or truth, or
love. Can you show me infinity? If you can't show it to me, how do you
know what it is? How can we agree what it is, if it does not exist in
material form?
Language allows you to say things you never said before and to understand
things you never heard before. It allows you to put your thoughts into a form
comprehensible by others. There are about 46 sounds, or phonemes, in English.
These 46 phonemes can be combined into 40,000 words. These words can be combined
into an infinite variety of sentences.
Words are like atoms, capable of infinite, but structured, configurations.
What is a word? Most people take for granted that they know what a word is,
until they're asked to define it. How does a child know what a word is?
A word
could be the smallest separate piece of a language that has meaning by itself.
Are words then the sounds between gaps in speaking? Most people don't realize
it, but people don't speak in discrete words. Spectrograms have revealed that
spaces come at intervals that do not correspond with word beginnings and
endings, but rather with the rhythm or inflection of the statement.
Sometimes language falls short. It is, for instance, rather limited in its
descriptions of such sensations as taste or smell. Novels often describe the
scent of human sweat as "rank" or of human urine as "foul."
This occurs when descriptive words do not exist; often in such cases metaphors
must, and often do, suffice. Representation can also come in handy. Ask someone to describe a spiral, and to do so
without gesticulating. It is possible to do, but not easy. In such cases, a
picture can be worth a thousand words.
On the other hand, language can sometimes convey what pictures can't.
The
sentence "Had I stepped on the brake, I would have skidded off the
road" is easily understood. Try to draw that.
Linguistics is defined as the science of language, particularly as to its
nature and structure. It is then about studying language. This study has three
crucial watermarks:
(1) Just over 200 years ago, scholars found that they could reconstruct
ancient languages from incomplete recovered scraps because all known
languages follow certain rules of development and change.
(2) At the turn of the recent century, students of language determined
systematic patterns marking all human tongues. Although the patterns vary,
they vary within certain parameters and do not violate those bounds.
(3) Finally, in 1957 with his book "Syntactic Structures" the
recognized progenitor of linguistics, Noam Chomsky, documented simple
rules underlying language patterns.
Words are limited: They must come one after the other, whether written on the
page, spoken from the mouth, or signed by the hands. They must bow to an
arrangement for comprehension to occur. Grammar and syntax comprise that
structure. Grammar allows the linkage between words and meaning, organizing
words according to rules. Syntax confers sequence and subtlety.
Grammar comprises the
frame of the structure while syntax adorns the interior. Consider the
subtle divergence between these
sentences:
"Yesterday I told you I loved you."
"I told you I loved you yesterday."
But grammar is not sufficient. Consider this sentence:
"Colorless green
ideas sleep furiously." The grammar is correct; the meaning is absent
(unless, in the years since Chomsky first uttered those words, they have taken
on a life of their own). The meaning of language is semantics.
To most of us, knowing perhaps a smattering of words in
other languages, enough to get us to the bathroom but no more, the array of working languages seems
incredible in its complexity. Yet Chomsky sees more in common among languages
than differences. To Chomsky, any two human languages have more in common than
a comparison between the
chirp of a bird and the bellow of an ox. Like faces, each of which is
unique but having in common two eyes, a nose, and a mouth, languages have
regularities.
Languages will, for example, to a greater or a lesser extent follow one
of two grammatic options: They will be based on either order or inflection.
Languages such as English that are based on order derive meaning from certain
allowed configurations. "The dog bit the boy" has meaning; "Bit
the the boy dog" does not. In inflection-based languages such as Latin,
word order is not important. Meaning is conferred by suffixes attached to words.
In Latin, then, the sentence "The farmer saw the ghost" could be
written "Agricola vidit umbram" (farmer saw ghost), "Agricola
umbram vidit" (farmer ghost saw), or "Umbram agricola vidit"
(ghost farmer saw) with equal clarity. Over time, languages change, and so will
emphasis on order or inflection.
Chomsky changed our view of language from that of a wooden and mechanical
inventory of facts to the question, "What is a possible human
language?," which expands naturally to "What is a possible human
being?," and ultimately to how the human mind works.
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The Fluidity of Thought
Are you a dualist or a monist? That is, do you believe that thought is a
manifestation of the soul, separate and distinct from the body, that existed
before the body and will persist when the body is gone? Or do you believe that
chemical and electrical activity in the proliferation of central-nervous-system
cells gives rise to the thought processes that we persist in claiming as our
own? Regardless of your perspective on the dualism/monism issue, do you
sometimes believe that reductionistic study of the brain, and experiments aiming
to gauge its function, somehow sidestep the issue of what really is the crux of
consciousness?
After winning a Nobel prize for work in immunology, Dr. Gerald M.
Edelman's studies set off in a most unlikely direction. He intends to crack the
question of how mind arises from brain. He is doing this by, once again, close
scrutiny of the structure of the brain, but with an emphasis on evolutionary
development provided by Darwin and the notion of natural selection.
Edelman began studying how synapses respond to messages from the outside
world and rejected the tabula rasa idea that the blank slate of
the brain simply reflected events. What provides the substrate for
responding to a never-experienced stimulus? How is it that we respond, for instance, to a
piece of music that we've never before heard? Contemplating the fantastic
complexity of the human brain, Edelman proposes that, in response to input from
outside and also to its own machinations, the brain constructs, or fashions, its
responses, and begins doing so even before language. This hypothesis launched
Edelman's research.
The neocortex, the new part of the human brain that wraps around the
remainder, laid flat is about the size, and thickness, of a large table napkin.
It contains about ten billion neurons, and the number of possible connections
among those neurons exceeds the number of subatomic particles in the universe as
it is currently conceived. Although it might seem reasonable that consciousness arises out of
such a fusion, that one's memories should contain such apparent lucidity
and consistency, which provides the individual with a coherent sense of self, is
perplexing. One theoretical solution to the puzzle is comparison of the brain to
a digital computer, based on Alan Turing's work. Known as connectionism, this
metaphor proposes neural networks that, through communications among themselves,
forge and fade links in an ongoing process.
Edelman vigorously rejects this
approach.
He considers the brain more akin to a complex and diversified jungle.
Whereas
a computer program is written before the fact and so can accommodate only what
it is programmed to do, Edelman sees neurons developing connections not only in
response to input but in an attempt to make sense of the chaos that confronts
us, and in ways unknowable before the proliferation occurs. Human response is
thus uniquely individual.
The theory of neuronal-group selection marries Darwin to neurology.
Not only
did evolution create consciousness in the human brain, the brain modifies this
consciousness through the course of a single lifetime. Neural Darwinism has
three components.
Developmental
selection: Much of the neural structure of the brain takes
place before birth. Before becoming fixed, individual neurons move within what
will become the cortex. In forming the germinal structure, some divide, some
die, and some affiliate with other neurons. These connections are consummated by
cell-adhesion molecules (what Edelman has dubbed "body glue"), which
are also journeying about the neocortex at that point in development and which,
when applied to adjacent neurons, form synapses. Edelman and his colleagues have
actually identified these molecules, which are potent evidence that brain
development is more opportunistic than fixed. Genes within the neurons provide
general, but not specific, instructions for eventual location of neurons and
connections between them. So while all human brains look alike on the surface,
the array of connections within them is singular.
Experiential selection: After birth, when the structure of the brain is
fairly well established, development of synaptic connections continues in
response to events throughout the remainder of life. In the Darwinian sense,
natural selection strengthens synaptic connections that are most practiced and
decays those that are discarded.
Reentry:
Although sounding downright aeronautical, this concept embodies Edelman's accounting of consciousness.
It is a
dynamic process best explained by the metaphor of the music of a string quartet,
performed without a conductor. The individual musicians, each of which possesses
his or her own internalized map of the performance, performs in tandem with the
others, responding to signals generated from them. From a multitude of possible
responses, the best is employed. Edelman calls the process reentry because it is
in constant flux.
The computer analogy implies that memories are retrieved from static
repositories and replayed like old movies. Yet trial lawyers are exquisitely
aware of the subtle changes in testimony obtained from perfectly candid
witnesses at each retelling of an event. Applying the concepts of neural
Darwinism and reentry, each time you reconsider the memory of, for example, your
first kiss could be deemed more a live reenactment from a theatrical troupe than
a static replay. If that is so, then the atmosphere of each reenactment could be
expected to color future performances. From the moment of birth, relative
associations among synapses are constantly shifting, strengthened with practice
or weakened by neglect, influenced by events without and within us, shaping our
minds.
| These articles are excerpts from
coursework provided under contract to Colorado State University and are
provided for illustrative purposes only. Commercial use is
strictly prohibited. |
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