Abnormal Psychology

Clinical Diagnosis and Assessment 91

We’ve just talked about how certain neuroimaging techniques can reveal brain

structure, but how can researchers observe brain functioning? A key fact is that when

a part of the brain is active, more blood (which transports oxygen and nutrients)

fl ows to it, a little like the way that more electricity fl ows into a house when more

appliances are turned on. The neurons draw more blood while they are sending and

receiving signals than they do when they are not activated, because the activity in-

creases their need for oxygen and nutrients. Because neurons in the same area of the

brain tend to work together, specifi c areas of the brain will have greater blood fl ow

while a person performs particular tasks.

In the fi eld of psychopathology, researchers use functional neuroimaging to

identify brain areas related to specifi c aspects of a disorder. For example, in one

study, researchers asked participants with social phobia, who were afraid of speak-

ing in public, to speak to a group and also to speak in private while their brains

were scanned. As shown in Figure 3.2, speaking in public activated key parts of the

limbic system, particularly the amygdala, more than did speaking in private (Tillfors

et al., 2001). As noted in Chapter 2, the amygdala is involved in strong emotion,

particularly fear. This part of the brain was not activated when people without a

social phobia were tested. Other researchers have reported similar results for other

sorts of phobias (Pissiota et al., 2003; Rauch et al., 1995).

The functional neuroimaging technique used in the study of social phobia

just described was positron emission tomography (PET), one of the most impor-

tant methods for measuring blood fl ow (or energy consumption) in the brain. PET

requires introducing a very small amount of a radioactive substance into the blood-

stream. While a person performs a task, active regions of the brain take up more

blood (and thus more of the radioactive substance) than less active regions. The

relative amounts of radiation from different areas of the brain are measured and

sent to a computer, which constructs a three-dimensional image of the brain that

shows the levels of activity in the different areas. In PET images, higher radiation

(greater activity) typically is indicated with brighter colors. PET scanning has draw-

backs, such as the need to introduce radioactive substances and the need to have the

person perform the same task for at least 40 seconds; in addition, a single test can

cost $2,000.

Computerized axial tomography (CT)

A neuroimaging technique that uses X-rays to

build a three-dimensional image (CT or CAT

scan) of the brain.

Magnetic resonance imaging (MRI)

A neuroimaging technique that creates

especially sharp images of the brain by

measuring the magnetic properties of atoms in

the brain; MRI allows more precise diagnoses

when brain abnormalities are subtle.

Positron emission tomography (PET)

A neuroimaging technique that measures

blood fl ow (or energy consumption) in the

brain and requires introducing a very small

amount of a radioactive substance into the

bloodstream.

3.2 • Social Phobia and

the Amygdala Results from PET

scans showing increased activation

in the region of the amygdala when

people with social phobia spoke

to an audience compared to when

they spoke in private; brighter

colors indicate greater activation.

The PET results are superimposed on

an MRI scan to show the location of

activated areas (Tillfors et al., 2001).

Figure 3.2

3 t s i p t t c T a a

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