374 CHAPTER 9
aspect of consciousness, characterized by three elements: a certain physical arousal, a certain
behavior that reveals the feeling to the outside world, and an inner awareness of the feeling.
THE PHYSIOLOGY OF EMOTION Physically, when a person experiences an emotion,
an arousal is created by the sympathetic nervous system. to Learning Objec-
tive 2.5. The heart rate increases, breathing becomes more rapid, the pupils dilate, and
the mouth may become dry. Think about the last time you were angry and then about
the last time you were frightened. Weren’t the physical symptoms pretty similar?
Although facial expressions do differ among various emotional responses (Ekman, 1980;
Ekman et al., 1969; Ekman & Friesen, 1978), emotions are difficult to distinguish from one
another on the basis of physiological reactions alone. However, in the laboratory using
devices to measure the heart rate, blood pressure, and skin temperature, researchers have
found that different emotions may be associated with different physiological reactions:
Sadness, anger, and fear are associated with greater increases in heart rate than is disgust;
higher increases in skin conductance occur during disgust as compared to happiness; and
anger is more often associated with vascular measures, such as higher diastolic blood
pressure, as compared to fear (Larsen et al., 2008; Levenson, 1992; Levenson et al., 1992).
The polygraph test was originally designed as a kind of “lie detector” test in the
early 1900s. The idea was that lying would produce different physiological reactions from
telling the truth (Bell & Grubin, 2010; Iacono, 2001). This assumption has proven to be
false: There is no specific, unique physiological reaction associated with lying versus tell-
ing the truth. There have been improvements added to the original polygraph test such
as the use of questions about knowledge that only the police, the victim, and the suspect
should know (Concealed Information Test, or CIT), but there is still a great deal of contro-
versy over the validity of the results (Ben-Shakhar et al., 2015; Palmatier & Rovner, 2015;
Vrij, 2015). While it may be a useful tool to convince suspects to confess to their crimes, it
really only detects the physiological correlates of emotion in general, not lying in specific,
and is not admissible as evidence of guilt or innocence in a courtroom in the United States.
Which parts of the brain are involved in various aspects of emotion? As discussed
in Chapter Two, the amygdala, a small area located within the limbic system on each side
of the brain, is associated with emotions such as fear and pleasure in both humans and
animals (Breiter et al., 1997; Davis & Whalen, 2001; Fanselow & Gale, 2003; Hurlemann
et al., 2010; Ritchey et al., 2011) and is also involved in the facial expressions of human
emotions (Morris et al., 1998).
When portions of the amygdala are damaged in rats, the animals cannot be clas-
sically conditioned to fear new objects—they apparently cannot remember to be afraid
(R. J. Davidson et al., 2000; Fanselow & Gale, 2003). In humans, damage to the amygdala has
been associated with similar effects (LaBar et al., 1995) and with impairment of the ability to
determine emotions from looking at the facial expressions of others (Adolphs & Tranel, 2003).
A lot of what we know about the amygdala’s role in emotion comes from the
work of Dr. Joseph LeDoux and his many colleagues and students. The amygdala is a
complex structure with many different nuclei and subdivisions, whose roles have been
investigated primarily through studies of fear conditioning (LeDoux & Phelps, 2008).
Fear conditioning has been very helpful in relating behaviors to brain function because
it results in stereotypical autonomic and behavioral responses. It is basically a classical
conditioning procedure in which an auditory stimulus (conditioned stimulus) is paired
with foot shock (unconditioned stimulus) to elicit autonomic and behavioral conditioned
responses (LeDoux, 1996; LeDoux & Phelps, 2008).
LeDoux’s work has provided many insights into the brain’s processing of emotional
information and the role of the amygdala. Emotional stimuli travel to the amygdala by both
a fast, crude “low road” (subcortical) and a slower but more involved cortical “high road”
(LeDoux, 1996, 2007; LeDoux & Phelps, 2008). (See Figure 9. 6 .) The direct route allows
for quick responses to stimuli that are possibly dangerous, sometimes before we actually
know what the stimuli are, but with the awareness provided by the indirect cortical route
