Behavioural Neurosciences
Chapter 1: Neurosciences: Past, Present, and Future
The origins of neuroscience
Evidence suggests that even our prehistoric ancestors appreciated that the brain was vital to life. The
archeological record includes many hominid skulls, dating back a million years and more. As early as
7000 years ago, people were boring holes in each other’s skulls (a process called trepanation). These
skulls show signs of healing after the operation, indicating that this procedure had been carried out on
live subjects. Some individuals apparently survived multiple skull surgeries. Recovered writings from the
physicians of ancient Egypt, dating back almost 5000 years, indicate that they were well aware of many
symptoms of brain damage. It is also very clear that the heart was considered to be the seat of the soul
and the repository of memories. The view that the heart was the seat of consciousness and thought was
not seriously challenged until the time of Hippocrates.
Views of the Brain in Ancient Greece
Consider the idea that the different parts of your body look different because they serve different
purposes. There appears to be a very clear correlation between structure and function. Differences in
appearance predict differences in function. The most influential scholar was Hippocrates (460–379
B.C.E.) who believed that the brain was not only involved in sensation but was also the seat of
intelligence. The famous Greek philosopher Aristotle (384–322 B.C.E.) clung to the belief that the heart
was the center of intellect. He believed it was a radiator for cooling blood that was overheated by the
seething heart. The rational temperament of humans was thus explained by the large cooling capacity of
our brain.
Views of the Brain During the Roman Empire
The most important figure in Roman medicine was the Greek physician and writer Galen (130–200 C.E.),
who embraced the Hippocratic view of brain function. Two major parts are evident: the cerebrum in the
front and the cerebellum in the back. Galen tried to deduce function from the structure of the cerebrum
and the cerebellum. Poking the freshly dissected brain with a finger reveals the cerebellum is rather hard
and the cerebrum rather soft. From this observation, Galen suggested that the cerebrum must receive
sensations while the cerebellum must command the muscles. He recognized that to form memories,
sensations must be imprinted in the brain. The cerebrum is largely concerned with sensation and
perception and a repository of memory, and the cerebellum is primarily a movement control center. In
these hollow spaces, called ventricles there is fluid. To Galen, this discovery fit perfectly with the
prevailing theory that the body functioned according to a balance of four vital fluids, or humors.
Sensations were registered and movements initiated by the movement of humors to or from the brain
ventricles via the nerves, which were believed to be hollow tubes.
Views of the Brain from the Renaissance to the Nineteenth Century
During the Renaissance, the great anatomist Andreas Vesalius (1514–1564) added more detail to the
structure of the brain. Hydraulically controlled mechanical devices supported the notion that the brain
could be machinelike in its function: Fluid forced out of the ventricles through the nerves might literally
“pump you up” and cause the movement of the limbs. A chief advocate of this fluid–mechanical theory
of brain function was the French mathematician and philosopher René Descartes (1596–1650). Although
he thought this theory could explain the brain and behavior of other animals, Descartes believed it could
not possibly account for the full range of human behavior.
,Uniquely human mental capabilities exist outside the brain in the “mind.” Descartes believed that the
mind is a spiritual entity that receives sensations and commands movements by communicating with the
machinery of the brain via the pineal gland. Today, some people still believe that there is a “mind–brain
problem,” that somehow the human mind is distinct from the brain. Two types of brain tissue were
observed: 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. 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. An important breakthrough in neuroanatomy came with the observation that
the same general pattern of bumps (called gyri) and grooves (called sulci and fissures) can be
identified on the surface of the brain in every individual. This pattern, which enables the parceling
of the cerebrum into lobes, led to speculation that different functions might be localized to the
different bumps on the brain. The stage was now set for the era of cerebral localization.
Nineteenth-Century Views of the Brain
The nervous system was understood at the end of the eighteenth century:
- Injury to the brain can disrupt sensations, 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.
Nerves as Wires
The new concept was that the nerves are “wires” that conduct electrical signals to and from the brain.
Within each nerve of the body there are many thin filaments, or nerve fibers, each one of which could
serve as an individual wire carrying information in a different direction. A curious anatomical fact is that
just 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. Bell found
that cutting only the ventral roots caused muscle paralysis. Bell and Magendie concluded that within
each nerve is a mixture of many wires, some of which bring information into the brain and spinal cord
and others that send information out to the muscles. 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 where they enter or exit the spinal cord.
Localization of Specific Functions to Different Parts of the Brain
If different functions are localized in different spinal roots, then perhaps different functions are also
localized in different parts of the brain.
Experimental ablation method = parts of the brain are systematically destroyed to determine their
function.
Phrenology = new ‘science’ of correlating the structure of the head with personality traits.
Broca was presented with a patient who could understand language but could not speak. After the man’s
death, Broca carefully examined his brain and found a lesion in the left frontal lobe. Based on this case
and several others like it, Broca concluded that this region of the human cerebrum was specifically
responsible for the production of speech. Similarly, German physiologist Hermann Munk using
experimental ablation found evidence that the occipital lobe of the cerebrum was specifically required
for vision. Today’s maps of the functional divisions of the cerebrum rival even the most elaborate of
those produced by the phrenologists.
,The Evolution of Nervous Systems
The idea that the nervous systems of different species evolved from common ancestors and may have
common mechanisms is the rationale for relating the results of animal experiments to humans. Most
neuroscientists today use animal models to examine processes they wish to understand in humans.
Consequently, rats provide a valuable animal model for research focused on understanding how
psychoactive drugs exert their effects on the nervous system. On the other hand, many behavioral traits
are highly specialized for the environment (or niche) a species normally occupies. Adaptations are
reflected in the structure and function of the brain of every species. By comparing the specializations of
the brains of different species, neuroscientists have been able to identify which parts of the brain are
specialized for different behavioral functions.
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, German zoologist Theodor Schwann proposed
what came to be known as the cell theory: All tissues are composed of microscopic units called cells.
Although cells in the brain had been identified and described, there was still controversy at that time
about whether the individual “nerve cell” was actually the basic unit of brain function. Nerve cells usually
have a number of thin projections, or processes, that extend from a central cell body.
Neuroscience today
Levels of Analysis
History has clearly shown that understanding how the brain works is a big challenge. To reduce the
complexity of the problem, neuroscientists break it into smaller pieces for systematic experimental
analysis. This is called the reductionist approach. The size of the unit of study defines what is often
called the level of analysis. In ascending order of complexity, these levels are molecular, cellular,
systems, behavioral, and cognitive.
Molecular Neuroscience
The brain has been called the most complex piece of matter in the universe. Brain matter consists of a
fantastic variety of molecules, many of which are unique to the nervous system. These different
molecules play many different roles that are crucial for brain function: messengers that allow neurons to
communicate with one another, sentries that control what materials can enter or leave neurons,
conductors that orchestrate neuron growth, archivists of past experiences. The study of the brain at this
most elementary level is called molecular neuroscience.
Cellular neuroscience = focuses on studying how all those molecules work together to give neurons their
special properties.
Systems Neuroscience
Constellations of neurons form complex circuits that perform a common function, such as vision or
voluntary movement. Thus, we can speak of the “visual system” and the “motor system,” each of which
has its own distinct circuitry within the brain. At this level of analysis, called systems neuroscience,
neuroscientists study how different neural circuits analyze sensory information, form perceptions of the
external world, make decisions, and execute movements.
Cognitive Neuroscience
Perhaps the greatest challenge of neuroscience is understanding the neural mechanisms responsible for
the higher levels of human mental activity, such as self-awareness, imagination, and language. Research
at this level, called cognitive neuroscience, studies how the activity of the brain creates the mind.
, Neuroscientists
Broadly speaking, neuroscience research (and neuroscientists) may be divided into three types: clinical,
experimental, and theoretical. Clinical research is mainly conducted by physicians (M.D.s). The main
medical specialties associated with the human nervous system are neurology, psychiatry, neurosurgery,
and neuropathology. Thus, there are neuroanatomists, who use sophisticated microscopes to trace
connections in the brain; neurophysiologists, who use electrodes to measure the brain’s electrical
activity; neuropharmacologists, who use drugs to study the chemistry of brain function; molecular
neurobiologists, who probe the genetic material of neurons to find clues about the structure of brain
molecules.
The Scientific Process
Neuroscientists of all stripes endeavor to establish truths about the nervous system. Regardless of the
level of analysis they choose, they work according to a scientific process consisting of four essential steps
- Observation. Observations are typically made during experiments designed to test a particular
hypothesis.
- Replication. Any observation, whether experimental or clinical, must be replicated. Replication
simply means repeating the experiment on different subjects or making similar observations in
different patients, as many times as necessary to rule out the possibility that the observation
occurred by chance.
- Interpretation. Interpretations depend on the state of knowledge (or ignorance) at the time and
on the scientist’s preconceived notions (or “mind set”). Interpretations therefore do not always
withstand the test of time.
- Verification. This step is distinct from the replication the original observer performed.
Verification means that the observation is sufficiently robust that any competent scientist who
precisely follows the protocols of the original observer can reproduce it. Successful verification
generally means that the observation is accepted as fact. Thus, the process of verification, if
affirmative, establishes new scientific fact, or, if negative, suggests new interpretations for the
original observation.
The Use of Animals in Neuroscience Research
The Animals
The choice of species is generally dictated by the question under investigation, the level of analysis, and
the extent to which the knowledge gained can be related to humans. As a rule, the more basic the
process under investigation, the more distant can be the evolutionary relationship with humans. Thus,
experiments aimed at understanding the molecular basis of nerve impulse conduction can be carried out
with a distantly related species, such as the squid. On the other hand, understanding the neural basis of
movement and perceptual disorders in humans has required experiments with more closely related
species, such as the macaque monkey.
Animal Welfare
Today, neuroscientists accept certain moral responsibilities toward their animal subjects:
1. Animals are used only in worthwhile experiments that promise to advance our knowledge of the
nervous system.
2. All necessary steps are taken to minimize pain and distress experienced by the experimental
animals.
3. All possible alternatives to the use of animals are considered.
