Cherish Madu

This wiki explores the methods that those interested in neuroscience most frequently employ when investigating and explaining cognitive processes in terms of brain structure and function and highlights the advantages and disadvantages of each method.

Neuroscience Techniques

Transcranial Magnetic Stimulation

Overview, Advantages, Disadvantages

Optogenetics

Overview, Advantages, Disadvantages

Electrophysiological recording of neurons

Overview, Advantages, Disadvantages

Electroencephalography

Overview, Advantages, Disadvantages

Positron Emission Tomography

Overview

Positron emission tomography (PET) is a three-dimensional brain imaging technique that takes advantage of changes in metabolism to localize brain activity and functional processes in the body. The most active parts of the brain use more metabolic processes than do relatively inactive parts of the brain and PET is able to track this metabolic flow. Flourine-18 or oxygen-15, the most commonly used radioactive tracer isotopes, is injected into the bloodstream where it disperses to more active parts of the brain. Inside the brain, the radioactive tracer decays into a positron and an electron. When the positron collides with an electron, two gammas rays are produced. The accumulation of these pairs of gamma rays is measured by gamma-ray detectors which are placed all around the subject's head. Computer analyses construct the radioactive tracer concentration into three-dimensional images. PET is often combined with CT or MRI scans for superimposition of the images of concentration onto anatomic images of the subject's brain.

PET is not only used in neuroimaging. It also has applications in oncology and pharmacology. Flourodeoxyglucose (FDG) is primarily used in oncology because of its ability to track glucose metabolism in cancer tissues. Flourodeoxyglucose flourine-18 (FDG-PET) is also used to detect patients at risk for stroke in cardiology.

Advantages

PET has the advantage of having high spatial resolution (approximately a centimeter). PET is also used in humans and can be used to study higher-order functioning that is relevant to our population.

Disadvantages

Radioactive isotropes need to be created by cyclotrons either on-site or near the hospitals using PET. This process is very costly. Moreover, because the positron has to travel before it collides with an electron to produce gamma-rays, temporal resolution is very low. It takes close to a minute for the concentration of gamma-rays to accumulate into a reliable signal. Also, PET is a somewhat invasive procedure because it requires the Injection of radioactive molecules into the bloodstream. However, the dose of radiation is reduced in isotopes with short half-lives.

Functional Magnetic Resonance Imaging

Like PET, Functional magnetic resonance imaging (fMRI) results in the imaging of active brain locations. fMRI, however measures blood flow using the blood-oxygen-level-dependent (BOLD) contrast.

References

Huettel, S. A.; Song, A. W.; McCarthy, G. (2009), Functional Magnetic Resonance Imaging (2 ed.), Massachusetts: Sinauer, ISBN 978-0-87893-286-3