130 Chapter 4 Neurons, Hormones, and the Brain
“Listening” to the brain with an EEG ma-
chine is like standing outside a sports stadium:
You know when something is happening, but
you can’t be sure what it is or who is doing it.
Fortunately, computer technology and statisti-
cal techniques can be combined with EEG
technology to get a clearer picture of brain ac-
tivity patterns and mental processes associated
with specific events, such as seeing a picture or
hearing a word.
• PeT (positron-emission tomography) scans record
biochemical changes in the brain as they are
happening. One type of PET scan takes advan-
tage of the fact that nerve cells convert glucose,
the body’s main fuel, into energy. A researcher
can inject a person with a glucoselike substance
that contains a harmless radioactive element.
This substance accumulates in brain areas that
are especially active and are therefore consum-
ing glucose rapidly. The substance emits ra-
diation, which is detected by a scanning device,
and the result is a computer-processed picture
of biochemical activity on a display screen, with
different colors indicating different activity lev-
els (see Figure 4.6a). Other kinds of PET scans
measure blood flow or oxygen consumption,
which also reflect brain activity. PET scans can
tell researchers which areas are busiest when
a person hears a song, recalls a sad memory,
works on a math problem, or shifts attention
from one task to another.electroencephalogram
(eeg) A recording of
neural activity detected
by electrodes.
PeT scans (positron-
emission tomography)
A method for analyzing
biochemical activity in
the brain, for example
by using injections of a
glucoselike substance
containing a radioactive
element.
examining the role of various brain regions in
everything from vision to emotion to language.
• Transcranial direct current stimulation (tDCS) is
an even newer way of studying brain function.
The researcher applies a small electric current
to an area of the cortex, the outer surface of the
brain (Nitsche et al., 2008). Depending on the
direction of the current, brain activity in that
area is temporarily stimulated or suppressed. In
one study, applying current in one direction in-
creased activity and improved people’s memory
for information gained during one task while
they focused on doing another. But applying
the current in the other direction, which re-
duced activity, decreased the participants’ abil-
ity to do this task (Zaehle et al., 2011).The other general approach to mapping the
brain is to do something that affects behavior and
then record what happens in the brain:• electroencephalograms (eegs) use electrodes, de-
vices pasted or taped onto the scalp to detect
the electrical activity of millions of neurons
in particular regions of the brain. Wires from
the electrodes are connected to a machine that
translates the electrical energy from the brain
into wavy lines on a moving piece of paper or
a screen, which is why electrical patterns in
the brain are known as “brain waves.” A stan-
dard EEG is useful but not precise because it
reflects the activities of so many cells at once.transcranial direct
current stimulation
(tDCS) A technique that
applies a small electric
current to stimulate or
suppress activity in parts
of the cortex; it enables
researchers to identify
the functions of a par-
ticular area.
Electrodes on the scalp (left) are used to produce an overall picture of electrical activity in different areas of the
brain. Transcranial magnetic stimulation, or TMS (center), delivers a large current through a coil on a person’s head,
causing neurons under the coil to fire. It can be used to temporarily disrupt specific brain circuits. Transcranial direct
current stimulation, or tDCS (right), applies a small electrical current to a specific area of the cortex, which stimu-
lates or suppresses activity in that region depending on the direction of the current.