Studying the Brain - Neuroimaging

With recent advances in medical technology, scientists have developed new ways of measuring brain activity and brain structure.

Measuring Brain activity

A visualization of the brain via MRI and PET scans. (Courtesy of the International Neuroimaging Consortium, University of Minnesota and the PET Imaging Center, Minneapolis VA Medical Center.)

One such device is called an electroencephalogram (EEG). An EEG detects tiny electrical currents on the surface of the brain, generated by surface neurons. Such a way of measuring electrical current within the brain allows researchers to pin point where there is increased brain activity when a subject performing certain functions, such as thinking, eating, and motor function. The limitation of the EEG, however, is that it is only able to scan the surface of the brain and is not able to penetrate into the inner part of the brain.

Scientists were able to go beyond the limitations of the EEG with the positron emission tomography (PET) scan. This type of scan allows the scientific phrase of a "three-dimensional localization of brain function" (Gleitman, 1999, p. 20), meaning viewing brain activity was no longer limited to the 2-D surface of the brain but now the whole brain. The PET scan works by injecting the patient with a safe dose of radioactive sugar (similar in structure to the sugar glucose). When cells take in the sugar, it emits particles called positrons which can be detected by a machine. Active neurons take in this radioactive sugar and emit positrons that are detected by the machine. The machine can measure the amount of positrons emitted and assemble an image of the brain showing the varying degrees of activity in the brain.

Determining Brain Structure

While determining brain activity is a useful way of determining what part of the brain does what, it is also useful to determine the definite structure of the brain. With such delicate techniques such as surgery, it is often useful to have a precise map of the human brain.

A model showing a combined 3-D MRI and PET scan. (Source:NIMH)

One of the techniques used for discerning a brain's structure is the computerized axial tomography (CAT) scan. This technique uses an instrument that works by exposing a person's brain to x-rays. These x-rays pass through the brain of the patient and are picked up by a detector on the other side. The machine repeats shooting x-rays and circles about an axis, making a roundabout the patient's head. Because the brain's regions are composed of different densities, not all the x-rays pass through the person's head. A computer takes the data from how many x-rays pass through the different densities of the brain and assembles a picture of what the patient brain looks like.

But perhaps the most commonly used neuroimaging technique is magnetic resonance imaging (MRI). An MRI scan is safer than a CAT scan because it doesn't involve potentially harmful x-rays. This technique works based on the principle of magnetic resonance. All the nuclei contained in atoms have their own resonant frequencies. When the atoms are agitated, their resonant frequencies change and become amplified. An MRI machine disturbs these atoms by passing a frequency alternating magnetic field through the brain. As the magnetic field fluctuates, it is picked up by magnetic sensors that sense how much the atoms in a particular area respond. A computer compiles an image of the brain based on how much these atoms are disturbed.

Studying the Brain - Neuroimaging