The Origins of Neuroscience
- Neuroscience is young; The Society for Neuroscience formed in 1970.
- Hippocrates first challenged the idea that the heart was responsible for memories and consciousness.
Views of the Brain in Ancient Greece
- Greek scholars of the fourth century BC realized that the brain is the organ of sensation.
- Most influential scholar was Hippocrates; found the brain is also responsible for intelligence.
- Idea was not widely accepted; Aristotle said heart is responsible for intelligence and that the
brain cools the blood that is overheated by the heart. The rational temperament of human was
thus explained by the large cooling capacity of our brain.
Views of the Brain During the Roman Empire
- The most important person is the Greek physician/writer, Galen, who agreed with Hippocrates view of
- Galen tried to deduce function from the structure of the cerebrum and cerebellum; the cerebrum is soft
and the cerebellum is hard and he therefore thought that the cerebrum must be the recipient of sensation
and the cerebellum must command the muscles. In this case, the right general conclusions were reached
from the wrong reasoning.
- Galen split the brain and saw ventricles, which he thought validated the prevailing theory that the body
functioned according to the balance of humors. This theory suggested that sensations were registered
and movement initiated by the movement of humors to or from the brain ventricles via the nerves, which
were believed to be hollow tubes, like the blood vessels.
Views of the Brain From the Renaissance to the 19 Century
- Galen’s view of the brain prevailed for almost 1500 years and the anatomist Andreas Vesalius added
more detail to the structure of the brain during the renaissance.
- Ventricular localization was strengthened in the early 17 century when inventors began developing
hydraulically controlled mechanical devices; these devices supported the notion that the brain could be
machinelike in its function.
- A main supported of this fluid-mechanical theory of the brain function was the French mathematician
and philosopher Rene Descartes. However, he did not believe it could control the full range of human
behavior. He said that unlike animals, humans have intellect and a God-given soul and that brain
mechanisms control human behavior only to the extent that this behavior resembles that of the beasts.
Uniquely human mental capabilities exist outside the brain in the “mind”. The mind and the brain were
believed to communicate through the pineal gland.
- Other scientists during the 17 and 18 century broke away from Galen’s obsession with the ventricles
and looked at the brain closer. They found that brain tissue id divided into two parts: the gray matter and
the white matter. White matter, because it was continuous with the nerves of the body, was correctly
believed to contain the fibers that bring information to and from the gray matter.
- By the end of the 18 century, the nervous system had been completely dissected and its gross anatomy
had been described in detail. Scientists recognized that the nervous system has a central division
(consisting of the brain and spinal cord) and a peripheral division (consisting of the network of nerves
that course through the body). Another breakthrough was that all individuals have the same general
pattern of bumps (gyri) and grooves (sulci) on the surface of the brain.
- This pattern was the basis for speculation that different function might be localized to different bumps.
- Summary of understanding of the NS by the end of the 18 century:
- Injury to the brain can disrupt sensation, movement, and thought, and can cause death.
- The brain communicates with the body via the nerves.
- The brain has different identifiable parts, which probably perform different functions.
- The brain operates like a machine and follows the laws of nature. 19 Century Views of the Brain
- Four key insights gained during the 19 century.
1. Nerves as fibers. Luigi Galvani and Emil du Bois-Reymond had shown the muscles can be caused to
twitch when nerves are stimulated electrically and that the brain itself can generate electricity. These
discoveries stopped the idea that the nerves communicate with the brain by the movement of fluid. The
new concept was that the nerves are “wires” that conduct electrical signals to and from the brain. Around
1810, Charles Bell and Francois Magendie noticed that before the nerves attach to the spinal cord, the
fibers divide into two branches, or roots. The dorsal root enters toward the back of the spinal cord, and
the ventral root enters toward the front. Cutting the ventral root caused muscle paralysis and the dorsal
roots proved to carry sensory information in the spinal cord. It was concluded that in each sensory and
motor nerve fiber, transmission is strictly one-way. The two kinds of fibers are bundled together for most
of their length, but they are anatomically segregated when they enter or exit the spinal cord.
2. Localization of Specific functions to Different Parts of the Brain. In 1811 Bell proposed that the origin of
the motor fibers is there cerebellum and the destination of the sensory fibers is the cerebrum. A
systematic ablation method in which parts of the brain are systematically destroyed to determine their
function was used to verify this idea. Marie-Jean-Pierre Flourens used this method in a variety of animals
and concluded that the cerebrum is involved in sensation and perception and the cerebellum does indeed
play a role in the coordination of movement, but unlike those before him, he has solid experimental
support. Next, Gall proposed that bumps on the surface of the skull reflect the bumps on the surface of the
brain and that certain personality traits could be correlated with the dimensions of the head, a “science”
known as phrenology. This idea fascinated the public was not taken seriously by the scientific community.
Florens himself disagreed with phrenology and believed that all regions of the cerebrum participate
equally in all cerebral functions, a conclusion that was later shown to be wrong. Broca is the one that is
actually credited with proving localization through his discovery that the left frontal lobe is responsible
for the production of speech. Solid experimental support for cerebral localization in animals quickly
followed: Gustav Fritsch and Eduard Hitzig showed in 1870 that applying small electrical currents to a
exposed surface of the brain of a dog could elicit discrete movement. David Ferrier repeated these
experiments with monkeys; in 1881 he showed that removal of this same region of the cerebrum causes
paralysis of the muscles. Hermann Munk using experimental ablation presented evidence that the
occipital lobe of the cerebrum was specifically required for vision.
3. The Evolution of Nervous Systems. In 1859, Darwin published On the Origin of Species. Darwin included
behavior as a heritable trait that could evolve. He noticed that many mammalian species show the same
reaction when frightened: the pupils get bigger, the heart races, hairs stand on end. To Darwin, the
similarities indicated that these different species evolved from a common ancestor, which possessed the
same behavioral trait. The idea that the Ns of different species evolved from common ancestors and may
have common mechanisms is the rationale for relating the results of animal experiments to humans.
However, many behavioral traits are highly specialized for the environment a species normally occupies.
Ex: rats sense of touch to the face is highly evolved, monkeys sense of sight is.
4. The Neuron: The Basic Functional Unit of the Brain. Technical advances in microscopy during the early
1800s gave scientists their first opportunity to examine animal tissues at high magnifications. In 1839,
Theodor Schwann proposed the cell theory: all tissues are composed of microscopic units called cells. By
1900, the individual nerve cell, the neuron, was recognized to be the basic function