in detail the structural and chemical properties of the soil

							Historical Views of Brain, Mind, and Behavior
(adapted from “Brain, Mind, and Behavior” 2nd. ed. by Floyd E. Bloom and Arlyne Lazerson)

The ancient Greeks kept some of the earliest
written records of humans thinking about the
ability to think. Heraclitus, a Greek philosopher
of the sixth century B.C., referred to the mind as
an enormous space whose boundaries could
never be reached, even by traveling along every
path.
  Speculation about the nature of mental activity
has probably gone on since thinking began, but
agreement on the source of mental activity is a
relatively recent accomplishment. In the fourth
century B.c., Aristotle wrote that the brain was
bloodless and that the heart was not only the
source of nervous control, but was also the seat
of the soul. (Aristotle is revered today more for
his invention of a systematic style of thinking
than for his neuroanatomical insights.) The early
dissectors of animal brains in the second century
A.D. took great care to assure the authorities that Leonardo da Vinci's passion for anatomy extended
they sought only for the center of the system of to dissection. In sketches like this one he follows the
                                                                 convention
nerves that caused the body to sense and move. medieval of which he of spherical ventricles, the
                                                        foremost            called the "common sense
For the next thousand or more years those who cell," where the soul was thought to reside.
examined the brain took the same precautions.
The church, after all, retained authority over human consciousness, the "soul," and the
soul, wherever it lay, was not subject to direct investigation.
Analysis by Analogy
Historians of science have observed that thinkers in the past tried to explain how the
brain and mind worked by using analogies to the physical world in which they lived. This
striking observation can be stated more poetically as "the metaphors of mind are the
world it perceives" (Jaynes, 1976). The Greek physician Galen, living in the second
century A.D., was one of the first to dissect the brains of humans and other animals. The
major technological achievements in his day were aqueducts and sewer systems that
relied on the principles of fluid mechanics. It is hardly accidental, then, that Galen
believed the important parts of the brain to lie not in the brain's substance but in its fluid-
filled cavities. Today these cavities are known as the cerebroventricular system, and the
fluid that is made there is called cerebrospinal fluid. Galen, however, believed that all
physical functions and states of health and illhealth depended on the distribution of four
body fluids, or "humors": choler (or blood), phlegm (or mucus), black bile, and yellow
bile. Each "humor" had a special function: blood carried the animal's vital living spirit;
phlegm caused sluggishness; black bile was responsible for melancholy; and yellow bile
aroused the temper.
                                                        So deeply were Galen's views ingrained in
                                                        Western thought that the role of humors in brain
                                                        and other organ functions remained largely
                                                        unquestioned for nearly 1500 years.
                                                           By the eighteenth century, more rigorous-
                                                        minded observers had begun to attack the
                                                        natural phenomena of the world "scientifically."
                                                        The undocumented and hypothetical constructs
                                                        of the past were replaced by the conviction that
                                                        everything could be explained in terms of
                                                        mechanics. It was now a world of machines.
                                                        The brain machinery of the sensing organs for
                                                        vision and hearing was the first to be revealed.
                                                        In the early seventeenth century, the German
                                                        astronomer Johannes Kepler argued that the eye
                                                        operated essentially like an ordinary optical in-
  The four humors. Counterclockwise from upper left:    strument, by projecting the image of what was
  too much black bile keeps a melancholic man in
  bed; yellow bile drives the choleric husband to wife- being seen onto the special sensory nerves of
  beating; phlegm makes a reluctant mistress; the       the retina, the light-detecting tissue at the back
  highblooded lover plays the lute for his lady.
                                                        of the eye. Some 75 years later, the description
                                                        of the mechanisms of the inner ear by the
English anatomist Thomas Willis led to the recognition that hearing was based on the
transformation of sound through the air by activation of special receptors of the cochlea,
a coiled tube of tissue within the inner ear.
These mechanistic discoveries gave rise to a split in thinking about body and mind,
which some scholars believe has caused problems ever since. Philosopher and mathe-
matician Rene Descartes is often cited as the father of this body-mind dualism.
Questions of biological science-that is, of what could be "known" about human beings
and other animals-could apply only to those structures they shared in common. The
processes of perceiving and examining the images received by these structures
belonged to a different and separate "mental" world reserved only for humans.
Although this permitted a mathematically accurate portrayal of the transformation of
optical and auditory images, it did not answer the deeper questions of how the
sensations received were synthesized into meaningful images of the world.
  During the sixteenth and seventeenth centuries, scientific advances gave rise to accu-
rate descriptions (but not actual explanations) of electricity. And as seventeenth-century
explorers spread out around the world, a more complete notion of the surface of the
earth was gained. The principles of both electricity and geography were eventually
applied to concepts of how the brain worked. However, change was slow. When the
important properties of the nervous system ceased to be regarded as the flow of humors,
this explanation was temporarily replaced by the theories of the "ballonists," who
considered the nerves to be hollow tubes through which the flow of gases excited the
muscles.
How did one disprove such a view? Scientists
dissected animals under water. When no gases
were observed to bubble up during muscle
contractions, the theory went flat.

  What new insight was gained from this
gruesome experiment? (Remember that al-
though electricity was known, its powers had
yet to be applied to practical uses. The industry
of this era, mid-seventeenth century, received
its power from windmills, flowing rivers, and
waterfalls.) Something had to flow from the
nerves to cause muscles to contract, so a "vital
fluid" theory replaced the gas theory. It was
reasoned that an "essence" of the hollow
nerves flowed into the muscle, mixed with its
fluids, and caused explosive contractions. This
"fluid" hypothesis was one of the first to be
issued from the newly formed Royal Society
of England, around 1661.
   The vital-fluid concept eventually gave way
                                                    Johannes Kepler portrayed the eye as an optical
to the view, proposed by the physicist Isaac instrument rather than a divine mystery. This view
Newton around the beginning of the eighteenth of body parts as being like other machines was
                                                    the breakthrough that allowed scientific research
century, that activity was transmitted by a to begin.
vibrating "aetherial Medium," one which had
all the properties later found to hold for biological electricity. Even with the primitive
instruments of the eighteenth and nineteenth centuries, it was rather easy to show that
both nerves and muscles were electrically excitable. However, the view that the nerves
and muscles themselves actually worked by generating animal electricity was not
immediately grasped. The Italian scientist Luigi Galvani solved this problem near the end
of the eighteenth century, and the German biologist Emil du Bois-Reymond reexamined
it early in the next century. Du Bois-Reymond was the first scientist to attempt an
explanation of all functions of the brain on the basis of chemical and physical grounds.
He and his coworkers were the first to measure in a convincing way the electrical
properties of living, active nerves and muscles.
Analysis by Observation and Experimentation
During the nineteenth century, medical investigators provided the next wave of under-
standing about the brain. Taking advantage of the unfortunate victims of the expanding
technology of war, medical observers could determine the exact locations of destructive
injuries, or lesions, in the brains of soldiers with nonfatal head injuries. Clinical observa-
tions, which connected specific neurologic or mental problems to specific areas of
damage to the brain, continue to serve as a major source of vital information.
Luigi Galvani's electricity-producing machine one day accidentally sparked a twitch in the leg
of a freshly dissected frog. The general observation that electrical stimuli can cause muscles
to contract set off the search for animal electricity."




The "lesion approach" was also applied experimentally to the brains of other animals in
order to find the locations of gross functions, such as response to touch or movement of
the limbs.
   The Austrian anatomist Franz Joseph Gall carried the concept of localized sensory and
motor regions in the brain one step further. Perhaps borrowing an idea from geography,
Gall proposed that all human mental faculties-from such well-accepted abilities as speech
and movement to detailed and inferential skills like dexterity, wit, and veneration of the
deity-could be located by charting the bulges in the skull that overlay the pertinent
physical structures of the brain. This transient science, known as phrenology, soon fell
out of favor. A corresponding strategy of animal brain research, however, was more
useful. Its proponents believed that the action for which a brain region was responsible
could be determined by seeing what happened when the region was electrically stim-
ulated. By the end of the nineteenth century, these two techniques of research-lesions and
stimulation-had enabled scientists to identify large functional segments of the brain.
   As physical scientists began to explore beneath the surface of the earth and examine in
detail the structural and chemical properties of the soil, brain scientists in the late
nineteenth and early twentieth centuries began similar "geological" examinations of what
lay below the surface structures of the brain. Lesions and stimulation experiments had
shown that the outer layers of the brain were essential for the highest forms of con-
sciousness and sensory responsiveness. By geological analogy, the layers beneath were
assumed to represent structures that were laid down earlier in evolution, the most
primitive being the deep structures of the midbrain and hindbrain. When these regions
were destroyed, animals could not survive.
   Further insight came from detailed analyses of brain structure. These efforts were led
by the success of the early microscopists, such as the English anatomist Augustus von
Waller, who discovered a chemical method that would detect strands of dying nerves (so-
called "Wallerian degeneration"). This chemical "stain" helped establish that the long
fibers of the nerves outside of the brain and spinal cord were actually extensions of the
cells inside the brain and spinal cord. Some of these large cells could even be seen with
the aid of the primitive microscopes. Although microscopes were available earlier, the
complex and compact cellular structure of the brain was not easily examined. More stains
were needed to highlight single cells selectively.
   Soon thereafter, by the 1880s, the Italian
Camillo Golgi and the Spaniard Santiago
Ramon y Cajal began to apply improved
staining methods intensively. Now the detailed
structures of the brain could be resolved into
two main classes of cells: the nerve cells, or
neurons, and the cells that appeared like glue
between the nerve cells, called neuroglia, or
sometimes just glia. Microscopic analysis of
the brain and its parts then became a third
critical "instrument" in the researcher's tool
box.




                                                         Palpation of bumps on the head became the rage after
 Layering of the cerebellum. At this very low power of
                                                         the introduction of phrenology in 1790. Everyone
 magnification, the nerve-cell nuclei appear as deep
 purple-blue spots. Three basic cellular layers are      wanted his or her head read-except, perhaps, those
 visible because of the density at which the neurons     with bumps around the ears, which stood for
 are packed.                                             combativeness, destructiveness, secretiveness,
                                                         acquisitiveness, and a devotion to food.
                 A Golgi-stained neuron from the cerebellar cortex of an adult rat.
               Following chemical exposure, this large Purkinje neuron has become
             totally impregnated with silver, giving it a near-black image that makes it
                stand out from the unstained cells around it. The elaborate dendritic
                          system arising from the cell body is clearly seen.



   The recognition that the tissue of the brain was composed of individual cells connected
by their extensions led to the question of how those cells worked together to perform the
work of the brain. For decades, arguments raged as to whether the process of
transmission between neurons was electrical or chemical. By the mid-1920s, however,
most scientists were willing to accept the current view, that the activation of muscles and
the regulation of the heartbeat and other peripheral organs occurs by the passage of
chemical signals arising in the nerves.
   This chemical-transmission hypothesis was clearly demonstrated in the experiments of
the English pharmacologist Sir Henry Dale and the Austrian biologist Otto Loewi. Their
discoveries led directly to the use of a fourth investigative strategy, the application of-
plant extracts and synthetic chemicals directly to the nerves and muscles in order to
compare their effects with those actually produced by the nerve. Although chemical
transmission was considered a necessary and sufficient explanation of the responses to
nerve signals in the limbs and viscera, its central role in the links between the neurons of
the brain and elsewhere took much longer to demonstrate.
A Contemporary Analogy
The complexity of the brain-even the brains of small animals-that has slowly emerged
from these hard-won discoveries staggers the imagination. The history of brain science in
the twentieth century has yet to be completely written. When it is, the working analogy
for the living brain might be the computer.
  Analogies often help scientists to model brain experiments according to some other
grand design already recognized in natureeither as we find it, as we see and observe it, or
as we imagine it to be. But no model, no matter how closely it simulates the operations of
the brain, will be completely acceptable until it can predict features of the brain's
operation that are not now readily apparent. The objective of brain scientists is not to
develop a model or a machine that can merely simulate or explain some of what we
already know the brain can do. Rather, the successful model will explain what the brain
does and how.


The Scientific Method

A true experimental science of the brain (or any other object of interest) requires a
method that allows for the establishment of certain facts, and then uses those facts to ask
better questions in order to gain more fundamental insights. The scientific method de-
pends on several separate components: (1) observation, the accurate recording of the
methods of study, the experimental conditions under which the observations were made,
and the results of the experiment; (2) interpretation, reasoning about the results in order
to generate hypotheses that can be used to frame future experiments, and (3) verification,
the repetition of the study by others, using the same conditions, in order to confirm or
question the results.
   The process of working from observations, to formulation of an integrative hypothesis,
to evaluation of the hypothesis experimentally is known as inductive reasoning. Scientists
who believe they work this way argue that they have no fixed ideas at the start but simply
allow nature to reveal itself through painstaking observations. A contrasting strategy,
attributed to Aristotle, is deductive reasoning, in which one starts with a global
hypothesis and then formulates experiments to test its truth.
   Most scientists probably use both strategies. It is virtually impossible not to have some
preexisting impressions, or intuitions, before an experiment, and it is equally impossible
to make observations without having these ideas somewhere in the background. Indeed,
unless you have some idea of what you are looking for, you probably cannot recognize it
when you see it. It is possible, however, when the data are presented according to the
rules of science, for one scientist to question another's interpretation. An outsider without
the discoverer's biases can, and often does, come up with another explanation of the
discoverer's results. The art of science, then, derives from an ability to look at someone
else's observations and devise new experiments that will confirm their accuracy or
suggest another explanation.

The Organization
of the Nervous System
        In order to describe "brain" properly, we must understand its relation to the
central and peripheral nervous systems. The central nervous system (or CNS) includes all
the parts of the nervous system that lie within
the bones of the skull and spine. The brain, therefore, is that part of the CNS enclosed
within the bones of the skull. The other major component of the CNS is the spinal cord.
        Nerves come into and out of the CNS, and once these nerves are beyond the bony
protective shelter of the skull and spine, they are considered to be parts of the peripheral
nervous system (PNS). One division of the PNS, the somatic (meaning "to the body"),
consists of the nerves that carry information from the skin, muscles, bones, and joints to
the spinal cord and from the spinal cord to the muscles. Some parts of the PNS, however,
have only remote connections with cerebrum and the “higher” brain functions. These
nerves are a division of the PNS called the autonomic nervous system (or ANS). For now
it is sufficient to know that the ANS is largely responsible for regulating the internal
environment: the heart, lungs, blood vessels, and other internal organs. In addition, the
digestive tract has its
own internal autono-
mous nervous system,
the diffuse enteric ner-
vous system, which
some neuroscientists
now consider to be a
third division of the
PNS.




                                       The Central Nervous System is wholly contained within the skull and
                                       vertebral column. The Peripheral Nervous System extends from these bony
                                       enclosures to the muscles and skin. The Autonomic and Diffuse Enteric
                                       Systems, other majors divisions of the peripheral nervous system, are not
                                       shown.
REVIEW QUESTIONS FOR YOUR READING


    i.. What was Aristotle's view of the brain and the heart?

    ii. What role did the church play in the early investigations of the brain?

    iii. What part of the brain most interested the second century anatomist named
    Galen? What were the functions of the four “humors?”

    iv. What contributions to neuroscience were made by Kepler and Willis?

    v. According to Descartes, what is the difference between “brain” and “mind?”

    vi. What did the balloonists believe?

    vii. Du Bois-Reymond believed that the functions of the brain could be explained
    by . . .

    viii. How did damage, or lesions to the brain, provide insights into brain function?

    ix. What is “phrenology” and who pioneered this concept?

    x. What happens to an animal when the midbrain or hindbrain are destroyed? How
    were these observations interpreted?

    xi. What contributions did Camillo Golgi and Santiago Ramon y Cajal add to our
    understanding of the brain?

    xii. Who suggested that communication between nerves and muscles was primarily
    chemical?

    xiii. According to this article, what are the three essential parts of the scientific
    method?