Neuroimaging: Three important brain imaging techniques

At the birth of neuroscience, it was difficult to understand how the brain worked because, at the time, those studying it did not have the technology to analyze and measure brain activity in real time. Thankfully, we have come a long way since the first dissections of the human brain, and we can use a multitude of wonderful pieces of technology that enable the study of the brain and its inner workings. 

Three different neuroimaging techniques, EEG, MRI, and PET, allow us to explore and measure the insane amounts of activity going on in our brain; however, each comes with its own strengths and limitations, making the motivations behind using them very important.

The Electroencephalogram (EEG)

The first neuroimaging technique we will start with is the electroencephalogram, also known as an EEG. An EEG measures electrical activities of the brain from hundreds of electrodes placed on the scalp with special glue and/or within a special cap. When neurons generate an action potential or “fire”, they generate an electrical field that is quite powerful. The electrodes placed on the scalp can detect this electrical activity and will transmit the information to a device that records the activity. When the brain activity is recorded, it looks a lot like random squiggly lines to the untrained eye; however, these electrical brain waves are anything but random and can be translated into different wave patterns. Examples of these patterns are shown to the right here, and will be displayed on a monitor that is connected to an EEG device.

As you can see, there are five basic wave patterns specialists look for. While these wave patterns appear separately here, in an actual EEG recording, the lines would be continuous and accurately identifying them takes a lot of training. Gamma waves (bottom) are associated with brain activity when we are actively learning and we have a heightened perception. Beta waves are associated with brain activity when we are awake, but not on high alert. In contrast to the latter two brain waves, alpha waves are associated with brain activity when we are relaxed, drowsy, or in a daydreaming state. Then we have theta and delta waves (top), which are respectively associated with brain activity when one is deep in thought and a deep sleep state. 

Specialists look for the abundance or lack thereof, for each wave type, and if there are abnormalities detected, they can be indicative of a neurological or mental disorder. An EEG can determine changes in brain activity that allow doctors to diagnose brain disorders, including seizure disorders like epilepsy, brain cancer (tumors), brain damage from head injuries, inflammation of the brain (encephalitis), stroke, and even sleep disorders.

Magnetic Resonance imaging (MRI)

The next imaging technique on our list is magnetic resonance imaging or MRI. This imaging method is a painless, non-invasive imaging technology that produces 3D detailed anatomical images of our brain, as well as our body. An MRI scanner consists of an outsized doughnut-shaped magnet that always encompasses a tunnel within the center. Patients are placed on a table that slides into a tunnel where brain and body scans occur.

During the examination, the scanner uses magnetic fields that emit radio waves to manipulate the magnetic position of the hydrogen protons of the body. The rotation and energy release of the protons are detected by a powerful antenna which sends the information to a computer. The computer analyzes the information, and through complex mathematical calculations, creates a clear, cross-sectional black-and-white image of the body. These images can be converted into
three-dimensional pictures of the scanned area, with the results looking
something like the images below.

From these specific MRI scans shown at the right, we can see the brain in two different planes (in various layers) where we can make out different brain structures like gyri (ridges of the brain; makes the brain look bumpy) and sulci (fissures on the brain; regions in between the ridges of the brain), the pons of the brain stem (thicker region of the brainstem at the base of the brain), and the cerebellum (brain structure located at the back, lowermost portion of the brain) among others. Isn’t it crazy that we can generate images such as these by manipulating little hydrogen protons?! 

MRIs are used to detect a variety of conditions throughout the body, as they provide clear images of body parts that can’t be seen as well as other imaging techniques like positron emission tomography. 

Positron Emission Tomography (PET)

The last type of neuroimaging I will discuss is positron emission tomography, otherwise known as PET. A PET scan is an imaging technique that helps reveal the functionality of one’s tissues and organs. To see this activity, radioactive tracers are used. These tracers tightly bind to glucose within the body. Whether it is swallowed, injected, or inhaled, when the tracer enters your body, it will travel through your bloodstream and collect in body and brain areas that require high levels of glucose. 

Neurons use glucose as fuel, therefore a PET scan can detect and measure brain activity using this method. When parts of the brain become active, blood (which contains the glucose-bound tracer) is sent to deliver the necessary glucose fuel, as well as oxygen. When the tracer accumulates in areas of the body such as the brain, it creates visible bright spots. These spots are then picked up by detectors within the PET scanner (which looks very similar to an MRI machine) and are used to create a video image of the brain.

We can see from these images the varying levels of neuronal activity, with the warmer colors representing higher levels of activity (red being the highest) and the cooler colors representing lower levels of activity. If we were to compare the detailedness of PET images to an image from an MRI, we can see that PET scans are better for measuring brain activity while MRI scans are better for analyzing the structural integrity of the brain.

If we were to compare the PET scans above, there are clear differences in brain activity between a neurotypical patient, who does not have Alzheimer’s Disease, and a patient who has advanced Alzheimer’s. When we look closely we can see there is a level of reduced brain activity between the two patients. This observation makes sense because patients who have been diagnosed with Alzheimer’s, experience neuronal damage and death (neurons dying) which results in less brain communication and activity, especially in areas associated with memory. 

In conclusion, imaging techniques such as EEG, MRI, and PET are each used to investigate different aspects of the brain. However, they are not the only approaches. The brain is a highly complex structure that is constantly adapting to new environments and situations. Although there is still a lot to learn about the brain, we have come a long way in our understanding of what it can all do AND thankfully we have advanced technology that allows us to have a glimpse of the immense activity going on. 

Edited by Clara Boothby and Dan Myers