We can use other methods to look at living human

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We can use other methods to look at living human brains. Neuroscientists have developed new techniques that effectively let us look at the brain as it functions. These techniques produce the spectacular photographs that show brains “lit up” in differ- ent colors while their owners think. They permit us to study the brains of living, conscious people, people who can report the mental gymnastics they are doing while we watch their brains doing them. These new techniques allow scientists to look globally at large areas of the brain, rather than at a single cell, and see how the brain works in concert. They show which brain areas are active when a person remembers the tune of “Yesterday,” hears a sentence about the World Series, sees a reproduction of a Monet water lily, or thinks about his mother. Either these methods record the brain’s electrical activity through the scalp, or they record the brain’s metabolic activity as it burns glucose, the body’s fuel. You can track the brain’s electrical activity from outside the skull with electroencephalograms (EEG), event-related poten- tials (ERP), and magnetoencephalography (MEG). In these experiments the subject wears a huge cap containing anywhere from twenty to two hundred electrodes (sometimes referred to as the hair dryer from hell) to pick up brain waves. As the person underneath the cap thinks about a certain thing or looks at a particular picture, the cap records the electrical activity of the person’s brain. Pat even tests young babies this way. Their caps are little and soft, like baby bonnets, and contain only twenty electrodes, but that is enough to record activity in the babies’ brains from many locations. Pat tests babies who listen to speech sounds through an earphone. The babies 178 / The Scientist in the Crib
are completely unaware that we are recording their brain waves while they listen. Other techniques, such as PET (positron emission tomo- graphy) and fMRI (functional magnetic resonance imaging), measure brain activity even more directly. PET exploits the fact that the more active parts of the brain burn more glucose, the brain’s fuel, than the less active parts, just as a more active muscle will burn up more calories than a less active one. In PET scans the brain is injected with radioactive glucose, and the scan traces which parts of the brain are burning up this glucose. The technique has been used primarily with patients who require brain surgery; it helps locate important structures that need to be avoided during the operation. The fMRI tech- nique also measures which regions of the brain are most active, and does this by tracking blood flow and oxygenation. The fMRI doesn’t involve injections and can even be used with children. Both of these techniques show activity in the brain more directly and in more detail than the methods that record from outside the brain. As the subjects do different things, listen to sounds or look at pictures or even just think, we can see which parts of the brain are getting a workout. The scans show that

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