Doctors and researchers use many different types of tools to look inside the human body. One tool called MRI, which stands for Magnetic Resonance Imaging, has become invaluable for its ability to safely produce images of different structures in the body using a powerful magnet and radio-waves. You may have had an X-ray before to help your dentist look at your teeth or show your doctor a broken bone. Having an MRI is similar to getting an X-ray because both technologies take still images of the body, but an MRI shows soft tissue like the brain, ligaments, and tendons, while X-rays show hard tissue like bones. In addition, X-rays can expose people to harmful radiation, while MRI scans do not cause negative health effects.
Caption: An x-ray (left) of a person’s head shows hard tissue like the skull and teeth, while an MRI scan (right) shows soft tissue like the brain. (artlex.com & stevebmd.files.wordpress.com)
In the 1990s, scientists figured out a way to use MRI to look at the activity of the brain instead of just its structure. They called their technique functional magnetic resonance imaging or fMRI. This development made MRI an attractive tool for researchers. They could now use it to study the brain’s response to things like pictures, sounds, and sensations, pick out regions of the brain that work together, and figure out what normal and abnormal brain activity looks like.
fMRI works by tracing the flow of blood throughout the brain. Regions of the brain that are in use typically require a greater supply of blood because blood carries sugar and oxygen, which cells need to make energy. As the blood rushes through the brain, it deposits its oxygen and leaves as de-oxygenated blood. fMRI imposes a large magnetic field on the brain and when de-oxygenated blood moves through it, the magnetic field is distorted. A computer measures the amount of distortion, allowing it to detect where blood is flowing in the brain. Images produced by fMRI show regions of the brain that are ‘activated,’ or have a greater than average amount of blood flowing to them.
The MRI machine is called a ‘scanner’, and the images that it produces are called ‘scans’. Although fMRI is a safe technology, it uses a large magnetic field so people working nearby the scanner or going inside of it cannot be wear any metal. For most people, this isn’t a problem because they can take off metal they might be wearing like watches and jewelry. Other people, however, may have permanent metal implants for health or dental reasons, and cannot go inside the MRI scanner. This means that MRI is not suitable for everyone. People going inside the scanner also need to be able to stay still for a long period of time, usually 30 minutes or more, because the body part being scanned needs to stay still while the machine takes many snapshots of it.
Despite these limitations, fMRI continues to be incredibly useful to doctors and researchers alike. Doctors use fMRI to map areas of the brain that are involved in critical functions such as speech and movement so that they can avoid these areas during surgery. Researchers have used fMRI to study diverse aspects of brain function including consciousness, emotions, sleep, vision, language and more. In several landmark studies, researchers identified a part of the brain that seems to recognize faces, which they dubbed the fusiform face area. When they showed pictures of faces to their participants in the fMRI scanner, they saw the blood flow in this part of the brain increase compared to when the same participants looked at pictures of non-faces, like objects or words.
Caption: The fusiform face area, activated during an fMRI scan (top left) and highlighted on a post-mortem brain (top right) is a region of the brain that responds to seeing faces (autism-center.ucsd.edu).
Recently, scientists in Budapest trained eleven dogs to sit still inside the MRI scanner long enough to record their brain activity. The researchers placed headphones over the dogs ears, asked them to lie perfectly still and played them sound recordings of human and animal noises. They then played the same sounds to humans while they were in the fMRI scanner to try to find commonalities between their brain activation. They found that dogs tended to respond to emotional sounds in a similar way that we do. Both the humans and the dogs in this study responded more strongly to positive noises than negative noises, and activated a similar region of the brain near the ears.
Clay, Rebecca. “Functional Magnetic Resonance Imaging: A New Research Tool.” American Psychological Association. American Psychological Association, 2007. Web. 28 Feb 2014. <http://www.apa.org/research/tools/fmri-adult.pdf>.
Doucleff, Michaeleen. “How Dogs Read Our Moods: Emotion Detectors Found In Fido’s Brain.” National Public Radio. National Public Radio, 21 Feb 2014. Web. 28 Feb 2014. <http://www.npr.org/blogs/health/2014/02/21/280640267/how-dogs-read-our-moods-emotion-detector-found-in-fidos-brain>.
“MRI vs X-Ray.” Diffen. Diffen. Web. 28 Feb 2014. <http://www.diffen.com/difference/MRI_vs_X-ray>.