Functional brain imaging helps scientists understand the relationship between particular types of mental activity and particular areas of the brain, by charting which regions experience increased blood flow or metabolism or electromagnetic activity over time. It’s a step beyond CT scans, or CAT scans, which can map the brain’s structure but not its functions. Click on the labels above to learn more about three technologies used for functional brain imaging."; brainscan_bcol_070102[i++] = new Array("","PET","","http://www.msnbc.com/news/wld/health/brill/images/brainscan_pet.jpg","","", "", "", "", "", "left", "", "", "150", "144", "", "", "", "", ""); brainscan_bcol_070102[i-1].body = "
Positron emission tomography
Radioactive tracers are injected into the circulatory system and concentrate in the areas of the brain where blood flow and metabolism are most active. When the radioactive material breaks down, it gives off a neutron and a positron. When the positron collides with an electron, both are destroyed and gamma rays are released. Detectors record the brain area where the gamma rays are emitted, providing a map of brain activity. PET scans can show quick changes in activity, but the machines are bulky and expensive.
More information from Encarta: “Radiology”
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Functional magnetic
resonance imaging:
MRI scanners detect the radio frequency signals produced by displaced radio waves in a magnetic field. Functional brain MRI scans can see the indirect effects of neural activity on blood volume, flow and oxygen consumption. The result is a map of the brain’s anatomy that can also point to changes in brain activity. Unlike PET scans, fMRI readings don’t require the injection of radioactive tracers. However, as with PET scans, the subject must lie still within a large, expensive machine.
More information from Encarta: “Magnetic Resonance Imaging”
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Electroencephalography and magnetoencephalography
The subject wears a “hairnet” of sensors that pick up electrical or magnetic impulses given off by brain waves in the cerebral cortex. Those impulses are charted over time, and a computer analysis can produce a changing two-dimensional map of cortical activity. The apparatus is less expensive and more portable than the machines used for PET or MRI scans, but the readings cannot measure activity or structure beyond the cerebral cortex. Thus, EEG or MEG is often combined with other methods.
More information from Wikipedia: Electroencephalography
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