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The PET Scan

Next came the PET scan. PET stands for positron emission tomography. Unlike CAT scans, which produce a three-dimensional still picture, PET scans can be made in real time. This means researchers can observe a PET scan change while a person thinks about various things. For example, PET scans can show which areas of the brain are activated by different ways of processing words. The following figure shows locations of one brain's response to seeing, hearing, speaking, or thinking of a word.

What is a major advantage of PET scans over CAT scans?

A PET scan shows four different responses.

PET scans show areas activated by seeing a word, hearing a word, speaking a word, or thinking a word.

Why does a PET scan often use glucose?

PET scans typically use glucose labeling. Glucose is the most common form of sugar in the body, and it is the brain's main source of energy. As brain cells consume chemically labeled glucose, positrons are emitted. The PET scan reveals which areas of the brain are burning the most sugar.

What are examples of specific activity detected by PET scans?

The results of PET scans are sometimes remarkably detailed. Pines (1981) reported the excitement of researchers seeing some of the first PET scans. A rat having its whiskers stroked produced different brain patterns according to which of five separate whiskers was touched.

Another study showed "the first physiological evidence of voices in a schizophrenic." This finding was replicated in the 1990s. Schizophrenics evidently generate language in the normal language-production areas of the brain that they interpret as somebody else's voice (Goleman, 1993).

Pitblado and Cohen (1984) studied a 32-year-old woman with a multiple personality (now called Dissociative Identity Disorder ). She had five different personalities. Pitblado and Cohen found that their patient had a different pattern of PET activation for each personality, although each personality was performing the same task in a laboratory.

PET scans were cutting-edge technology during the first half of the 1980s, but they require a subject to ingest glucose labeled with a radioactive tracer. PET scans can only be done two or three times a year on the same person before radioactivity becomes a hazard. Fortunately, cognitive neuroscience researchers now have several techniques available which do not require any exposure to radiation or ingestion of labeled substances. These techniques—such as functional MRI—are also capable of producing images more detailed than PET scans.

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