We use strong magnets to create high quality pictures of the brain. A strong magnetic field, combined with radio frequency waves (such as those detected by your FM radio), create detectable "echoes" from water molecules within brain tissue. From these "echoes," we can reconstruct a picture of the brain tissues themselves. This non-invasive technique is called "Magnetic Resonance Imaging" (MRI). Over the past decade, MRI has become an invaluable tool for diagnosing various medical conditions.
The brain is a collection of nerve cells, called "neurons." These neurons do all of the work we associate the brain, including seeing, feeling, and thinking.
To work properly, neurons need a constant supply of fuel and oxygen. Blood vessels transport these necessary chemicals to all of the brain cells. When the brain is working on a task, a particular set of neurons associated with that particular task work harder than the rest of the brain cells. These neurons require more nutrients and oxygen; therefore, the blood supply to them increases. Then, fuel and oxygen move from the blood into the cells, which changes the magnetic properties of the blood. We can use fMRI to measure these changes in magnetic properties.
fMRI techniques are often used to characterize memory. For example, if you were told to dial a particular number, a part of your brain would work harder to keep that number in your memory. This part of your brain would require more oxygen and nutrients. We can then use fMRI to image the changes in blood supply, pinpointing the location of those neurons in the brain.
[Adapted from the work of J. Pekar and P. Barker, 1999.]