Neuroscientists use four main methods to measure brain activity and correlate it with behavior: 1) examining brain anatomy using CT or MRI scans; 2) recording brain activity during tasks using EEG, MEG, PET, or fMRI scans; 3) studying the effects of brain damage; and 4) examining the effects of stimulating specific brain areas using transcranial magnetic stimulation or injecting chemicals. However, interpreting the results of brain stimulation experiments is challenging because behaviors involve multiple brain regions.

2.  Neuroscientists use a variety of methods to
measure behavior in both people who have
neurological disorders and those who do not.
When they are using methods to measure
brain activity, they are doing it using one of
the following four methods:

3. 1. Attempting to correlate brain anatomy with behavior. In this
case they are looking to see if people who are showing unusual
behavior have unusual characteristics in their brains as
well, such as some sort of damage.
1. Recording brain activity during behavior. In this
case, neuroscientists might record changes in the brain’s
activity during various types of behavior, such as
sleeping, solving problems, or being really active.
1. Examining the effects of brain damage. If the brain is
damaged, or if the brain is temporarily inactive for some
reason, it is useful for neuroscientists to see if some parts of a
person’s behavior are not occurring properly as well.
1. Examining the effects of stimulating (making more active) a
particular brain area. In this way, a neuroscientists is able to
see if a brain is not working properly because of damage in
some area of the brain and if this can be improved by
stimulating that particular area.

4.  Theresearch methods used by
neuroscientists to correlate brain
anatomy and behavior include
computerized tomography (CT) and
magnetic resonance imaging (MRI).

5.  With computerized tomography, a dye is injected
into the blood by a physician. The die will help
increase contrast so that the image produced by
the CT scan will be clearer. A person’s head is
then placed into a CT scanner and X-rays are
passed through the head. These X-rays are
detected on the opposite side. While the X-rays
are being passed through the head, the CT
scanner is rotated slowly until measures of the
brain have been taken over 180 degrees. From
the measurements that have been taken, a
computer then constructs images of the brain.

6. Picture showing a CT scanning machine, the location of a brain
tumor, and the way the tumor looks on the image produced by
the CT scanner.

7.  Another method of seeing how brain anatomy and
behavior work together is called magnetic resonance
imaging (MRI). Atoms with an odd-numbered atomic
weight have an axis of rotation that can be
measured. An MRI device uses a powerful magnet
field to cause the axes of rotation to align in a
particular way, and then tilts them with a brief radio
frequency field. Then the radio frequency field is
turned off, and the atomic nuclei release
electromagnetic energy (the energy associated with
something that is electric or magnetic) as they return
to their original axis. The MRI devise measures that
energy and produces an image of the brain. To get
the measures, a person has to lie perfectly still in the
devise, and it is very noisy as it makes the image. It
may be a bit scary for children or for people who are
afraid in a small space.

8. Magnetic Resonance Imaging (MRI) image of the brain

9.  Methods that neuroscientists use to record brain
activity during behavior include an
electroencephalograph (EEG),
magnetoencephalograph (MEG), positron-
emission tomography (PET), and functional
magnetic resonance imaging (fMRI). By using
these methods, neuroscientists can see what
your brain is doing and how it changes when you
are trying to solve a math problem, when you
are feeling scared, or when you just had a
pleasant surprise, for example. They want to
know what part of the brain is active and how
the brain changes as your behavior changes.

10.  When neuroscientists use an
electroencephalograph to measure brain
activity, they use electrodes (sometimes just
a few and sometimes more than a hundred)
that are placed on the outside of the head.
These electrodes are temporarily glued in
place with glue that is easy to remove with
an alcohol wipe. These electrodes measure
the average amount of activity at any point
in time for the cells that are directly under
the electrode. The neuroscientist then
amplifies and records the resulting image
that is produced.

11. Person with electrodes attached to her head in
preparation for an EEG scan

12. A magnetoencephalograph (MEG) is similar to
an electroencephalograph, but it doesn’t
measure electrical activity. Instead, it
measures the magnetic fields that brain
activity produces naturally. MEGs are very
sensitive and can measure changes in the
brain’s activity from one millisecond to
another.

13. Person in a MEG machine

14.  Positron-Emission Tomography (PET) allows a
neuroscientist to have a high-resolution image of brain
activity by recording the production of radioactivity from
chemicals that are injected into a person. The person gets
an injection of glucose or some other chemical that
contains radioactive atoms (an atom with an unstable
nucleus, which releases electromagnetic radiation). As the
radioactive atom decays, it releases a positron (an
elementary particle with positive charge). The positron
collides with a nearby electron (an elementary particle
with negative charge), and this causes the release of two
gamma rays (high-energy electromagnetic radiation) in
opposite directions. The person’s head is surrounded by a
set of gamma ray detectors. When two detectors record
gamma rays at the same time, they select a spot halfway
between the two gamma rays as the place where the
gamma rays originated. A computer then takes this
information and calculates the area of the brain with the
most blood flow. An area with the most blood flow is
usually the area with the most brain activity. A picture of
the area with the most brain activity is then produced.

15. PET scan image of the
top of the head

16.  With functional magnetic resonance imaging
(fMRI), neuroscientists use a modified version
of the MRI that is based on hemoglobin (the
blood protein that binds oxygen). The fMRI
can measure the oxygen used by the
brain, and the most active brain areas use
the most oxygen. Because the fMRI devise
can measure oxygen levels as they change in
different parts of the brain, it can measure
brain activity as it changes from one point in
time to another and from one behavior to
another.

17. fMRI scan of the brain. The red areas are the ones
showing the highest level of brain activity

18.  Neuroscientists can use some of the techniques
we have described already to measure people
who have had some type of brain damage from
injury or disease. But it is difficult to come to
any conclusions about how a specific area of the
brain is affected by a specific kind of
damage, because the kind of damage and the
specific areas of the brain that are damaged can
differ from person to person. So neuroscientists
need a method to “create” the brain damage, at
least temporarily so that they can see what the
specific brain effects are of a specific type and
in a specific place where brain damage occurs.

19.  The gene-knockout approach uses a
biochemical (using a chemical approach with
living things) to produce a mutation is a
particular gene. This can be used as a
method to affect certain types of
cells, neurotransmitters, or receptors of
neurotransmitters. This method is more
likely to be used with animals than with
humans.

20.  With the transcranial magnetic stimulation
approach, a neuroscientist can use an intense
magnetic field in a specific area of the head to
temporarily cause the neurons below the
magnetic field to no longer be active. With this
method, a neuroscientist can study a particular
person’s behavior with the brain area
active, then inactive, and then active again to
see how behaviors change. You would be able to
have some idea of how a specific brain area can
affect behavior with this method, but you would
not know why the behavior changed. Behaviors
have to be studied using a lot of different
conditions to know for sure how a specific area
of the brain affects a specific behavior.

21. Transcranial
magnetic
stimulation devise

22.  Neuroscientists can use electrodes inserted into
the brain areas they want to study with
laboratory animals the effects of brain
stimulation.
 With humans, neuroscientists will use
something that doesn’t require inserting
something into the brain. They can apply a
magnetic field to the head and stimulate the
brain areas under it. If the magnetic stimulation
was too strong, the brain areas would become
inactive. However, if the magnetic stimulation is
brief and mild, the brain area is stimulated, and
the researcher can record the activity produced
with some of the methods described above.

23.  Another way neuroscientists might stimulate
particular brain areas is to inject a chemical that will
stimulate a particular kind of receptor. In this
case, the neuroscientist would be stimulating all the
receptors that are sensitive to the chemical, and not
those in only a single area.
 A problem with brain stimulation is that most
behaviors and experiences depend on many brain
areas, not just one. So providing stimulation may not
produce a natural response.
 All methods neuroscientists use to study the brains of
humans have certain drawbacks as well as
advantages, and neuroscientists who study the brain
must choose the method carefully depending on what
specific information they hope to discover.