90 CHAPTER 3
information might provide clues for possible treatments. Although neurological
(and other biological) factors are not generally part of the DSM criteria for diagnos-
ing mental disorders, the search for neurological and other biological markers or
indicators of various psychological disorders has proceeded at a rapid pace over the
past decade. It is clearly only a matter of time before these sorts of factors will be
part of the standard diagnostic criteria for many psychological disorders.Assessing Abnormal Brain Structures
with X-Rays, CT Scans, and MRIs
Some psychological disorders, such as schizophrenia, appear to involve struc-
tural abnormalities of the brain. This is why clinical assessments sometimes make
use of scans of a patient’s brain. Neuroimaging techniques provide images of the
brain. The oldest neuroimaging technique involves taking pictures of a person’s
brain using X-rays. A computer can then analyze these X-ray images and reconstruct
a three-dimensional image of the brain. Computerized axial tomography (CT) (to-
mography is from a Greek word for “section”) builds an image of a person’s brain,
slice by slice, creating a CT scan (sometimes called a CAT scan).
A more recent technology, magnetic resonance imaging (MRI), makes
especially sharp images of the brain, which allows more precise diagnoses when
brain abnormalities are subtle. MRI makes use of the magnetic properties of
different atoms, which resonate at different frequencies. Here’s the basic idea:
First, a large magnet is turned on, which causes atoms in the brain to line up
with its magnetic fi eld. Each atom has a north and south pole. Because opposite
magnetic poles attract and like poles repel, the atoms become aligned with the
magnetic fi eld. Second, another magnetic fi eld, presented from a different angle,
is activated. This fi eld will turn some of the atoms away from their alignment
with the fi rst fi eld. Which atoms are affected by this second fi eld? This depends
on the rate at which this second fi eld is pulsing: Different kinds of atoms reso-
nate with different frequencies of pulses and align with this second magnetic
fi eld. The crucial part of an MRI is that when the second fi eld is turned off com-
pletely, the atoms that had lined up with it will now reorient themselves with the
fi rst fi eld. When the atoms that oriented with the second fi eld move back to be
aligned with the fi rst one, they create a signal that can be recorded. This signal
is translated into an image that shows where the atoms were located. By detecting
different atoms and combining the signals into images, MRI can indicate the
location of damaged tissue and can reveal particular parts of the brain that are
larger or smaller than normal. For instance, an MRI can reveal the shrinkage
of brain tissue that typically arises with chronic alcoholism (Rosenbloom,
Sullivan, & Pfefferbaum, 2003); had Rex Walls had an MRI, it might well have
shown that his brain had such shrinkage.
CT scans and MRIs can provide amazing images of the structure of the living
brain. For example, some people with schizophrenia have larger ventricles (inte-
rior, fl uid-fi lled spaces in the brain) than do people who do not have the disorder
(Schneider-Axmann et al., 2006). These larger ventricles may occur, at least in part,
because some of the surrounding brain tissue is smaller than normal, particularly in
the thalamus (Gaser et al., 2004).Assessing Brain Function With PET Scans and fMRI
Some mental disorders are associated not with abnormal brain structures (physical
makeup), but rather with abnormal brain functioning (how the brain operates). By
analogy, a laptop computer can fail to read CDs because the drawer for the CD
won’t open or the disk won’t fi t in the slot (a structural problem) or because the
program that reads the disks gets corrupted (a functional problem). In a similar
way, the brain can produce abnormal thoughts, feelings, and behaviors because
either its structure or its functioning is awry. Researchers use different types of brain
scans to assess brain functioning.People with schizophrenia tend to have abnor-
mally large ventricles (fl uid-fi lled spaces in the
brain). Compare these two images: The ventricles
are indicated by the red arrows.
SchizophreniaNo schizophreniaDaniel Weinberger, M.D. NIMH Clinical Brain Disorders BranchP SN