The essential observation was that when neural activity increased in a particular area of the brain, the MR signal also increased by a small amount. The discovery that MRI could be made sensitive to brain activity, as well as brain anatomy, is only about 20 years old. Observed with functional magnetic resonance imaging. Spontaneous fluctuations in brain activity However, mapping brain structure is not the same as mapping brain function.įox MD, Raichle ME. The MR image is a map of the distribution of the MR signal, and by manipulating the timing of the RF pulses and the delays before detecting the signal MRI is a sensitive tool for detecting subtle changes in brain anatomy. When a radio frequency (RF) magnetic pulse is applied at the right frequency, these hydrogen nuclei absorb energy and then create a brief, faint signal (the MR signal) that is detected by the RF coils in the MRI system. When you lay in the strong magnetic field of an MRI system all of the hydrogen nuclei in your body, most of which are in water molecules, tend to align with that magnetic field. Using the phenomenon of nuclear magnetic resonance (NMR), the hydrogen nuclei can be manipulated so that they generate a signal that can be mapped and turned into an image. It works by exploiting the fact that the nucleus of a hydrogen atom behaves like a small magnet. MRI has become a standard tool for Radiology because it provides high resolution images with good contrast between different tissues.
It is being used in many studies to better understand how the healthy brain works, and in a growing number of studies it is being applied to understand how that normal function is disrupted in disease.Ĭourtesy of Dr. Functional magnetic resonance imaging (fMRI) is a technique for measuring and mapping brain activity that is noninvasive and safe. Even when you rest quietly with your eyes closed the brain is still highly active, and the patterns of activity in this resting state are thought to reveal particular networks of areas that often act together. The brain also has many specialized parts, so that activities involving vision, hearing, touch, language, memory, etc. In your brain the activity of the neurons constantly fluctuates as you engage in different activities, from simple tasks like controlling your hand to reach out and pick up a cup of coffee to complex cognitive activities like understanding language in a conversation.
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