4/25/2003 - Functional magnetic resonance imaging (fMRI) has generated considerable excitement in the scientific world, because it offers a non-invasive way to image neuronal activity in the brain and thus study how the brain functions, sees and learns.
Its important to recognize the limitations of the technique, however, and to realize that scientists have a lot to learn about it, John C. Gore, Ph.D., director of the new Vanderbilt Institute of Imaging Science, said during a mini-symposium last week.
The event, titled From Sensation to Cognition: Large-scale Network Approaches to Understanding the Brain, was sponsored April 18 by the Vanderbilt Brain Institute.
Other speakers included Jon Kaas, Ph.D., Centennial Professor of Psychology at Vanderbilt, who discussed the organization and evolution of sensory and motor systems in the monkey brain; and Dr. Marsel Mesulam, director of the Cognitive Neurology and Alzheimers Disease Center at Northwestern University, who discussed the mapping of cognitive domains onto large-scale neural networks in the human brain.
Functional magnetic resonance imaging measures changes in the magnetic properties of blood as it transports oxygen to brain tissue in response to increased neuronal activity.
Neuronal activation requires energy, Gore said. To get the energy, the blood flow increases, bringing oxygen and glucose. The net effect is you wash out deoxygenated hemoglobin (hemoglobin that has given up its oxygen) from tissue, and the MRI signal increases.
The signal change is due to the blood oxygen level dependent (BOLD) effect, and it provides an in-direct measure of brain activity. To conduct the test, the subject lies down in an MRI machine with his or her head placed in the center of the doughnut-shaped magnet that is used to detect the MRI signal.
The subject is then asked to look at a picture, or listen to sounds, or perform a physical function, such as tapping his or her finger during the study. The BOLD signal can then be used to pinpoint the area of the brain involved in the cognitive function.
There are numerous studies showing that the BOLD signal changes with skill, learning, intervention and behavior, said Gore, who is Chancellors University Professor of Biomedical Engineering and Radiology. But many everyday factors, ranging from the subjects age to his or her consumption of caffeine, can affect the signals and may contribute to differences between individuals, he cautioned.
Can we use this to analyze learning in real time? he asked. It will take a very large number of studies.
Gore, who has a Ph.D. in physics from the University of London, came to Vanderbilt last July from Yale University, where he directed the Nuclear Magnetic Resonance Research Center and chaired the Biomedical Engineering Program.©2013 Vanderbilt University Medical Center