techniques. The images are used to measure the size and volume of the whole brain or specific areas within the brain.
To study brain functions, researchers use scans that show
physiologic activity inside the brain. You’ve probably seen
these studies covered in the press. The coverage usually
includes statements like “X is the part of the brain that ‘lights
up’ when people do Y.” Older functional scans—
electroencephalography (EEG) and single-photon emission computed
tomography (SPECT)—measure patterns of nerve activity or
blood flow, respectively. Newer methods, such as positron
emission tomography (PET), use radioactive tracers that can
be seen in the brain.
Much of what we know about dopamine function in the
brain results from the radioactive tracer raclopride, which is
injected into the body and attaches to empty dopamine receptors. Raclopride binding is higher in the brains of children or
adults with ADHD, so we “see” that their dopamine activity
levels are low. Raclopride binding drops to normal levels an