Functional magnetic resonance imaging
Functional magnetic resonance imaging (usually abbreviated fMRI[1]) is used to measure activity in the brain. This neuroimaging technique is based on the principle that neurons require blood to function, and so neural activity can be inferred by tracking blood flow. FMRI machines produce images of where neural activity occurs in the brain based on the blood-oxygen-level-dependent signal.
It has been known since 1890 that the active areas of the brain use more blood than when they are inactive,[2] although it took until 1980 to develop a method of tracking this change. [3] Red blood cells contain hemoglobin, a protein which stores oxygen, and carries it all around the body. Active neurons consume oxygen from hemoglobin. Hemoglobin is oxygenated when it is carrying oxygen, and deoxygenated when is depleted. Oxyhemoglobin is paramagnetic, which means it slightly repels a magnetic field, while deoxyhemoglobin is diamagnetic, which means it is slightly magnetic. A magnetic resonance imaging machine is able to detect these changes in magnetic properties, and creates an image based on the blood-oxygen-level-dependent (BOLD) signal.
FMRI is used to research the areas of the brain that are specialized for information processing. Studies have confirmed several previously known anatomically distinct areas in the visual cortex,[4] the motor cortex,[5] and language areas.[6]
References
- ↑ The f is written in lowercase unless at the beginning of a sentence.
- ↑ Roy, C. & Sherrington, C. (1890). On the regulation of the blood supply of the brain. ‘’Journal of Physiology’’ 11, 85-108.
- ↑ Ogawa S, Lee TM, Nayak AS, Glynn P (1990). "Oxygenation-sensitive contrast in magnetic resonance image of rodent brain at high magnetic fields". Magn Reson Med 14 (1): 68–78. PMID 2161986.
- ↑ Belliveau JW, Kennedy DN, McKinstry RC, et al (1991). "Functional mapping of the human visual cortex by magnetic resonance imaging". Science 254 (5032): 716–9. PMID 1948051.
- ↑ Kim SG, Ashe J, Georgopoulos AP, et al (1993). "Functional imaging of human motor cortex at high magnetic field". J. Neurophysiol. 69 (1): 297–302. PMID 8433133.
- ↑ Binder JR, Frost JA, Hammeke TA, Cox RW, Rao SM, Prieto T (1997). "Human brain language areas identified by functional magnetic resonance imaging". J. Neurosci. 17 (1): 353–62. PMID 8987760.