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Methods Used to Study the Brain
The brain's functions can be studied in many ways: effects of brain damage, effects of electrical,
chemical (and recently magnetic) stimulation of the brain, measurement of electrical and chemical
activity of the brain, and computer-based brain scans, which show structure or function of the brain
through the intact skull.
Figure 2-2a. Location of
the main brain areas where damage produces disturbed judgment and planning, impulsiveness, etc
(front) or disturbed visual functioning (back).
- Effects of brain damage. Damage to different brain areas produces different behavioral
and psychological effects. For example, damage in the front end of the brain disturbs the ability to
make decisions and to inhibit socially inappropriate behaviors. In contrast, damage to the back of the
brain disturbs vision. Figure 2-2a illustrates the location of these two areas.
- Effects of electrical and chemical stimulation.
- Electrical stimulation at different places in the brain selectively affects specific
psychological processes. For example, James Olds and Peter Milner (1954;
Olds, 1967) used electrical stimulation of small brain areas in rats to find a system in the brain that is
closely tied to reward. Rats with fine wire electrodes implanted into several connected areas of the brain
would work very hard to turn on brief pulses of electrical stimulation through those electrodes. To see
brief videos showing this rewarding effect of brain stimulation, click HERE Note that the
captions use the words" pleasure" and "pleasure center" rather loosely.
- Chemical stimulation. Psychologically active medications (lile antischizophrenic
medications, anesthetics, antianxiety medications) and recreational drugs (like nicotine in tobacco, LSD,
heroin, cocaine) selectively affect different mental processes because they selectively act on the brain in
different specific brain systems. Very small amounts of psychologically active
chemicals can be injected directly into specific small areas of the brain through thin cannulas (~tubes).
Such experiments have helped identify the location and function of brain systems that mediate (~carry
out) the effects of these chemicals. For example, the stimulant amphetamine (street name "speed")
directly affects the same brain system in which electrical stimulation produces the strongest reinforcing
and rewarding effects (Olds, 1967).
EEG pattern in waking (top) and in deep sleep. The EEGs show about 2 seconds of activity (horizontal
- Recording electrical activity from the brain.
- Recordings from the scalp. In 1929 Hans Berger discovered that electrical
signals from the brain can be picked up through the scalp from silver disk electrodes pasted to it. These
signals are called EEGs (which stands for electroencephalograms) or, informally, "brain waves."
Figure 3-2a shows the EEGs for wakefulness (top) and deep sleep (middle and bottom). For a
description of the EEG and its use to map how the brain works, click HERE.
- Recordings from the brain. Very thin wire or glass tube electrodes, so thin they
produce virtually no damage, can be put inside the brain itself(usually in experimental animals).
Electrical signals from the brain show different patterns of activity associated with different mental
processes. Figure 4-2a shows the response of a single nerve cell in the olfactory (smell) system to two
different odors. When nerve cells are excited they show more of the impulses each second. When they
are inhibited the show fewer or none,
Figure 4-2a. Response of a single nerve
cell in the olfactory (smell) system to two odors. In record A, the nerve cell responds with a large
increase in the rate (number/second) of impulses to Stim 1 but does not change in response to Stim 2.
In record B, the neuron does not change its rate of impulses in response to Stim 1 but stops all impulses
in response to Stim 2.
- Chemical measurements of brain activity. In the past 20 years, several methods have
been developed to measure chemical concentration and changes in concentration in small bits of the
brains of awake, normally behaving rats and other animal species.
- Computer-based brain scans. Starting about 1970, several computer-based devises
were introduced that show the structure and function of the brain non-invasively (the scalp and skull are
not opened). They provide picture of the brain as a series of slices, like the ones in Figures 3-2a and 4-
2a. Because they involve minimal invasion into the body, brain scans allow the study of brain structure
and function in normal healthy volunteers, as well as people with diseases of the brain (or other parts of
- Devices that show brain structures. The CT (or CAT) scan is a rotating X-ray
machine hooked up to a computer programmed to reconstruct slices through the brain from the x-ray
measurements. The MRI uses changes in an intense magnetic field. It shows more detail than does the
CT scan. They show the anatomy of the brain, allowing identification of brain damage and measurement
of the size of different parts of the brain. For example, many people suffering from more severa cases of
schizophrenia show smaller than normal-sized areas, especially in the front of the brain.
- Devices that show brain function PET and fMRI scans measure the changing activity
of each part of the brain. PET detects rapidly decaying radioactive atoms that are injected into the veins.
fMRI uses changes in an intense magnetic field. Both methods measure changes in blood flow
throughout the brain to show how active each small area of the brain is. The works because blood flow
changes very rapidly in an area as it increases or decreases its activity. Such scans have shown that
many people suffering from schizophrenia have abnormally low activity in the very front of the brain and
may have abnormally high activity in a specific place on the side of the brain.
Figure 3-2a. Right: CT
scan showing a horizontal slice through the brain. Left: Approximate position of the slice.
. Figure 3-2a shows shows a CAT scan as a horizontal slice through the brain. (The top of the
slice is the front of the brain.) Figure 4-2a shows a PET scan comparing the brains of a normal person
and a person suffering from obsessive-compulsive disorder. To go to an explanation of how PET works,
click HERE. To go to an explanation of how
MRI (also called NMR) works, click
HERE. (Some background in physics is very helpful.)
Figure 4-2a. Brain activity in a normal person and in a
person suffering from obsessive-compulsive disorder