How do researchers use various techniques to study the brain's structure and function?
Here is a collection of summaries and images of some of the most commonly used techniques.
ABLATION
Ablation is a term that describes any sort of surgical damage to tissue by burning or freezing. This could be done to any type of tissue from the skin, as in some forms of plastic surgery, to the brain and heart. In the brain, ablation is typically performed on animals to determine the behavioral effects of damage to specific brain areas. Below is an example of how this can be used to destroy a tumor.
ABLATION
Ablation is a term that describes any sort of surgical damage to tissue by burning or freezing. This could be done to any type of tissue from the skin, as in some forms of plastic surgery, to the brain and heart. In the brain, ablation is typically performed on animals to determine the behavioral effects of damage to specific brain areas. Below is an example of how this can be used to destroy a tumor.
LESION
A lesion is tissue damage resulting from disease, and in the brain this may be caused by injury, illness, tumor, or aneurysm (burst blood vessel). This can alter proper cognitive function and behavior, so we have learned a lot about areas in the brain and their specialized functions by studying people and animals with lesions in various locations.
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| This picture shows a lesion on an MRI scan that is located in the brainstem area, which in this case was a tumor that was causing the patient to have difficulty breathing and vomit frequently | . |
EEG
Kind of like an EKG measure’s the heart’s electrical activity, the EEG measures the brain’s electrical activity in the cerebral cortex. This is done by placing many electrodes on the scalp (either directly, or by applying a special cap).
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| The guy kind of looks a bit like Pinhead from Hellraiser, but the electrodes don't hurt |
The EEG traces below are examples of brain activity during various stages of sleep. One of the advantages of EEG technology is that it can quickly measure changes in brain activity. However, EEGs are limited in terms of pinpointing specific locations of activity, and do not have the ability to measure activity deep within the brain.
CT/CAT SCAN
A CT/CAT scan produces a 2D image based on x-rays taken around a single axis by inserting the body part into a a scanner that kind of looks like a big donut. The image produced is an inside view of the brain on which possible abnormalities may be detected. The CT/CAT scan can depict both bone and soft tissue, although the images of soft tissues are not very detailed. In addition, this type of scan strictly shows us brain structure, not the function of various brain areas.
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| In this CT scan, you can see the patient's eyes, parts of the temporal lobes, and the cerebellum in the back |
MRI
MRI is similar to CT/CAT scanning in that it allows us to see brain structure, rather than function. An MRI uses a large magnetic field to reconstruct an image of the body/brain. One of the advantages of the MRI over CT/CAT scanning is that it uses magnetic and radio waves rather than x-rays, which are safer. Also, the MRI image has much greater resolution and contrast, which means we can see the structure of soft tissue in a lot more detail, making it easier to tell the difference between normal and abnormal tissue. In addition, the MRI can scan on multiple axes, so we can look at “slices” of the brain from the top-down or from the front-back. A disadvantage is that because of the magnetic field, it cannot be used on patients with metal objects in their body (schrapnel, pins, dental braces, rods or plates), and the scanner itself requires that the patient lie still in very tight quarters, which can bother some people who have trouble lying flat on their backs, those with uncontrollable movements, and those who fear enclosed spaces.
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| In these MRI scans, you can clearly see the enlarged butterfly-shaped ventricle (fluid-filled space) in the brain of the identical twin who has schizophrenia (on the right) compared to the brain of his brother, who does not have schizophrenia (on the left.) |
fMRI
The fMRI is an MRI scan with the added capability of measuring neural activity (function) in specific brain areas. This is done primarily by measuring blood flow, which is greater to areas that are functioning while a patient is performing a specific task (such as reciting something, listening to a stimulus, or viewing visual stimuli). As shown in the image below, the areas that are brighter yellow are the ones with the greatest blood flow, and are therefore the most active. This image comes from an interesting (but not replicated) fMRI study that was done on brain activity while viewing Facebook pages. A disadvantage is that the fMRI does not accurately show the functioning of specific neural networks.
PET
PET scans use a radioactive isotope of glucose to measure the metabolic processes of cells in various brain and body areas. A cell needs to metabolize glucose when it is active and needs energy, so researchers can view the areas of the brain that are active during cognitive functions. Although a PET scan does not provide for the level of detail that an MRI does, there are some cognitive functions that are more completely depicted across the brain this way. Again, a disadvantage is that we can’t see function at the level of neural networks. The image below is kind of fuzzy compared to a normal PET image.
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Positron emission tomography (PET) scan of a person on cocaine Cocaine has other actions in the brain in addition to activating reward…The scans show where the cocaine interferes with the brain's use of glucose - or its metabolic activity. The left scan is taken from a normal, awake person. The red color shows the highest level of glucose utilization (yellow represents less utilization and blue shows the least). The right scan is taken from a cocaine abuser on cocaine. It shows that the brain cannot use glucose nearly as effectively - show the loss of red compared to the left scan. There are many areas of the brain that have reduced metabolic activity. The continued reduction in the neurons' ability to use glucose (energy) results in disruption of many brain functions. TMS TMS helps researchers measure brain function by briefly exciting neural activity in the top 2-3 cm of the cerebral cortex, which can stimulate a chain reaction of neural activity and increase the release of neurotransmitters in the stimulated area. More intense stimulation may also cause other neurons to temporarily become inactive due to overstimulation. This can result in the stopping of neural activity in the region, which may result in the patient being unable to complete a given task during stimulation. When this occurs, psychologists can reasonably assume the area being stimulated is vital to that task. Disadvantages include brief discomfort at the scalp in the area being stimulated, and the risk of seizure (especially in those who already suffer from epilepsy). An advantage of TMS is that is now approved as (an expensive, but) non-drug alternative in the treatment of severe depression which is safer and has fewer side effects than electroshock therapy. |
