NEUROSCIENCEMETHODS

WHAT BEHAVIORS DO NEUROSCIENTISTS MEASURE? 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:

CONT.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.

2. 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.

3. 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.

4. 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.

WHAT ARE METHODS THAT CORRELATE BRAIN ANATOMY AND BEHAVIOR?

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

COMPUTERIZED TOMOGRAPHY (CT)

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.

CT SCAN

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.

MAGNETIC RESONANCE IMAGING (MRI)

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.

MRI IMAGE

Magnetic Resonance Imaging (MRI) image of the brain

WHAT ARE METHODS THAT RECORD BRAIN ACTIVITY DURING BEHAVIOR? 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.

ELECTROENCEPHALOGRAPH (EEG)

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.

EGG SCAN

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

MAGNETOENCEPHALOGRAPH (MEG)

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.

MAGNETOENCEPHALOGRAPH (MEG)

Person in a MEG machine

POSITRON-EMISSION TOMOGRAPHY(PET)

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.

PET SCAN

PET scan image of the top of the head

FUNCTIONAL MAGNETIC RESONANCE IMAGING (FMRI) 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.

FMRI

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

WHAT ARE METHODS THAT RECORD THE EFFECTS OF BRAIN DAMAGE? 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.

GENE-KNOCKOUT APPROACH 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.

TRANSCRANIAL MAGNETIC STIMULATION 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.

TRANSCRANIAL MAGNETIC STIMULATION

Transcranial magnetic stimulation devise

WHAT ARE METHODS THAT RECORD EFFECTS OF BRAIN STIMULATION? 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.

CONT 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.