A commonly used research method in cognitive psychology is brain scans. There are different neuroimaging techniques that work in different ways, for example MRI scans and PET scans have different functions and are based on different principles. Neuroimaging techniques can generally be divided into two types: functional and structural techniques, but which techniques fall under which of these two types?
- Neuroimaging techniques
- Structural neuroimaging techniques
- MRI
- CT-scan
- Functional neuroimaging techniques
- fMRI
- PET scan
Neuroimaging techniques
Neuroimaging techniques are applied in various fields. Brain scans, which are the focus of neuroimaging techniques, often play a major role in making certain diagnoses of diseases and conditions. Brain scans also help determine the cause of a mental illness. Using this information, cognitive psychologists can then find out what role a certain part of the brain or neural network plays in people’s behavior.
Structural neuroimaging techniques
The neuroimaging techniques that display the anatomy of the brain belong to the structural neuroimaging techniques. Using this type of brain scan, tumors can be visualized, among other things. The volume of the white and gray matter that makes up the brain can also be determined. If brain damage is detected in a specific part of the brain and the patient shows symptoms of a certain cognitive disorder, this information can be used to learn more about the part of the brain in question. An experiment requires multiple participants to properly investigate the connection between the brain damage in question and cognitive disorder. Two commonly used structural neuroimaging techniques are MRI and CT scans.
MRI
MRI is an abbreviation for Magnetic Resonance Imaging. This type of brain scan does not use X-rays, such as a CT scan, but uses a magnetic field and the magnetic properties of the atoms in the brain tissue. This ensures that this technique is completely harmless as long as there are no metal objects in or on the body. During an MRI scan of the brain, the patient lies on a table and the head is placed in a hollow cylindrical magnet or between two loose plates. The specific type of atoms used in MRI scans are protons, also known as hydrogen atoms. The electromagnetic radiation gives the electrons of the hydrogen atom more energy. These excited hydrogen atoms then emit energy in the form of radio waves, which is measured by a coil. The contrast between tissues visible in the final images is determined by the speed at which the excited atoms return to their normal energy level. This is also called the ground state in physics. Details in the anatomy of the brain can be observed because tissues have different hydrogen densities and thus radiate different amounts of energy. In this way a three-dimensional image of the brain can be made.
CT-scan
CT is an abbreviation for Computer Tomography. Another name by which the CT scan is also known is the CAT scan, which stands for Computerized Axial Tomography. This type of brain scan uses X-rays, just like a normal X-ray. A CT scan makes a cross-section of the body. By making multiple cross-sections taken from different angles, a three-dimensional image can be formed by combining these cross-sections. The CT scan measures the degree of absorption of the X-rays, just like a normal X-ray. However, the difference between a CT scan and a normal X-ray is that a higher dose of radiation is used when making a CT scan. This type of brain scan can show brain structure and focal lesions as well as a number of abnormalities in the brain that are related to, for example, the size of a brain part. It is also possible to observe dead brain tissue and tumors with the image provided by a CT scan. Blood vessels can be difficult to see on X-rays; If necessary, a contrast agent can be used to still visualize the blood vessels in question.
Functional neuroimaging techniques
Functional neuroimaging techniques show the circulation of fluids in the brain. These types of techniques mainly use the blood circulation in the brain. All activities in the brain are caused by neurons that communicate with each other through a complex network. However, not all neurons have the same function. Neurons can be part of a specific network associated with a specific type of behavior. Neurons, like other types of cells, require nutrients obtained through the blood. By looking at the metabolism in the brain, it can be determined which parts of the brain are active and which are not, because where there is more activity, more metabolism takes place. In this way, for example, it can be analyzed which parts of the brain work together and through experiments it can be discovered how this happens.
fMRI
Similar to MRI, fMRI also uses a magnetic field. The difference is that fMRI, also known as functional magnetic resonance imaging, works with oxygen. Oxygen can bind to hemoglobin, which ensures that oxygen is transported through the bloodstream. Deoxygenated hemoglobin, or hemoglobin without bound oxygen, disrupts the magnetic field in which the patient lies, while hemoglobin with bound oxygen does not. It is thought that more blood and therefore more oxygen flows to the area in question when more cells are active. However, this does not mean that the consumption of oxygen suddenly becomes much greater, as happens with glucose, for example. Because oxygenated and deoxygenated hemoglobin have different magnetic properties, this increase in oxygenated hemoglobin is noticed by the fMRI scanner. The scanner measures the BOLD contrast, the blood oxygen dependent contrast. The BOLD contrast can be seen as an indication of the activity of neurons, or to be precise, the rate at which the neurons fire signals. Because neurons become more active during cognitive activities, the BOLD contrast can also be seen as an index of cognitive activity. This makes it possible to study which neural networks and brain parts are involved in certain cognitive activities, such as decision making.
PET scan
Positron Emission Tomography, or a PET scan, also works with the blood circulation in the brain to detect brain activity. With a PET scan, brain activity can be traced over a short period of time using radiotracers, a special camera and a computer. This technique not only measures blood flow, but also glucose metabolism and oxygen uptake. A commonly used radiotracer is the isotope oxygen-15, which decays after one minute. This can be administered by having the patient drink a cup of water containing the radiotracer. In an experiment, a cognitive task can be performed after taking the radiotracer. The radio racer will then appear on the scan. In this way it can be accurately determined which parts of the brain are active during the performance of the task.