Chapter 4 Neurons, Hormones, and the Brain 131that these images can convey oversimplified and
sometimes misleading impressions (see Figure 4.7).
Color can be used to either accentuate or mini-
mize contrasts between two brains; small contrasts
can be made to look dramatic, larger ones to look
insignificant (Dumit, 2004). Combining individual
brain scans into one average scan—a common
practice—may mask significant variability among
people’s brains.• Magnetic resonance imaging (Mri) uses power-
ful magnetic fields and radio frequencies to take
highly detailed pictures of bodily organs. The
magnets produce vibrations in the nuclei of atoms
making up the organ in question. The vibrations
are then picked up as signals by special receivers.
A computer analyzes the signals, taking into ac-
count their strength and duration, and converts
them into a high-contrast picture of the organ
being studied, such as the brain (see Figure 4.6b).
An ordinary MRI image gives us a terrific
picture of what the brain looks like, although not
what it does. But an ultrafast version of MRI, called
functional Mri (fMri), allows us to see brain activ-
ity associated with specific thoughts or behaviors
lasting at least several seconds. It can capture brain
changes many times a second as a person performs
a task, such as reading a sentence or solving a
puzzle (see Figure 4.6c). In fMRI, the receivers
detect levels of blood oxygen in different brain
areas. Because neurons use oxygen as fuel, active
brain areas produce a bigger signal. Scientists are
using fMRI to correlate activity in specific brain
areas with everything from racial attitudes to moral
reasoning to spiritual meditation. Whenever you
read about a new specialty with “neuro” in front of
it—neuromarketing, neurofinance, neurolaw, even
neurocinematics—you can be sure its proponents
are using fMRI (though not always wisely).
Controversies and Cautions. Exciting though
these developments and technologies are, we need
to understand that technology cannot replace criti-
cal thinking (Legrenzi & Umiltà, 2011; Tallis, 2011;
Wade, 2006). Because brain-scan images seem so
“real” and scientific, many people fail to realize
Mri (magnetic
resonance imaging) A
method for studying body
and brain tissue, using
magnetic fields and spe-
cial radio receivers.fMri (functional
magnetic resonance
imaging) A fast version
of MRI used to study
brain activity associated
with specific thoughts
and behaviors.Figure 4.7 Coloring the Brain
By altering the colors used in a PET scan, researchers
can create the appearance of dramatic brain differences.
These scans are actually images of the same brain.Figure 4.6 Scanning the Brain
In the PET scans on the left, arrows and the color red indicate areas of highest activity, and violet indicates areas of low-
est activity, as a person does different things. In the center, an MRI shows a child’s brain, along with the bottle he was
drinking from while the image was obtained. On the right are fMRI images made while a person was listening to music.
(a) (b) (c)