268 CHAPTER 7
Neurological Factors
Brain systems, neural communication, and genetics contribute to panic disorder and
agoraphobia. Specifi cally, these three types of neurological factors appear to give
rise to a heightened sensitivity to breathing changes.Brain Systems
One key to explaining panic attacks came after researchers discovered that they
could induce attacks in the laboratory. Patients who had had panic attacks volun-
teered to hyperventilate (that is, to breathe in rapid, short pants, decreasing carbon
dioxide levels in the blood), which can trigger panic attacks. Moreover, researchers
found that injections of some medically safe substances, such as sodium lactate
(a salt produced in sweat) and caffeine, produced attacks—but only in people who
have panic disorder (Nutt & Lawson, 1992; Pitts & McClure, 1967). Why do these
substances induce panic attacks? One possibility is that they trigger a brain mecha-
nism that warns us when we are suffocating (Klein, 1993). According to this theory,
the brains of people who experience panic attacks have a low threshold for detect-
ing decreased oxygen in the blood (Beck, Ohtake, & Shipherd, 1999; Papp, Klein, &
Gorman, 1993; Papp et al., 1997).
As predicted by this theory, patients with panic disorder cannot hold their
breath as long as control participants can (Asmundson & Stein, 1994). When trig-
gered, the neural mechanism not only produces panic, but also leads to hyperventi-
lation and a strong sense of needing to escape. The need to escape is consistent with
the fi nding that the right frontal lobe is activated more than the left when people
with panic disorder see stimuli that are likely to induce panic symptoms, such as a
photograph of an emergency situation (Wiedemann et al., 1999). Why? Researchers
have documented that a key part of the right frontal lobe is more strongly acti-
vated when people experience withdrawal emotions (such as fear) than when feeling
approach emotions (such as joy) (Davidson, 1992). In addition, as noted earlier,
the frontal lobes have direct connections to the amygdala (a subcortical structure
that is involved in feeling strong emotions) and to the hypothalamus (a subcorti-
cal structure that is involved in the fi ght-or-fl ight response) (Gabbott et al., 2005;
Ghashghaei & Barbas, 2002; Teves et al., 2004). Indeed, the frontal lobe helps to
regulate the limbic system and hence plays a central role in both the triggering and
modulating emotions (LeDoux, 1996, 2000).
Thus, the data suggest that withdrawal emotions—which prompt escape from
a situation—are relatively easily induced in people with panic attacks. These emo-
tions may be triggered by the sense of impending suffocation, which in turn may
activate the limbic system and autonomic nervous system, as in the fi ght-or-fl ight
response. However, research fi ndings do not show that all panic attacks are a result
of a suffocation reaction or that all such attacks are accompanied by activation of
withdrawal mechanisms in the brain. In fact, researchers have documented two types
of panic disorder, one based on a lower threshold for detecting suffocation (Abrams,
Rassovsky & Kushner, 2006) and one based on learning (Acheson et al., 2007).Neural Communication
Researchers have been investigating the role of neurotransmitters and neuromodu-
lators in giving rise to panic disorder. One key neurotransmitter is norepinephrine,
too much of which is apparently produced in people who have anxiety disorders
(Nutt & Lawson, 1992). To explain this fi nding, some researchers have focused
on a small subcortical structure called the locus coeruleus, which is located in the
brainstem. The locus coeruleus produces norepinephrine, and some have theorized
that it is too sensitive in people with panic disorder (Gorman et al., 1989) and
thus may produce too much norepinephrine. The locus coeruleus and norepineph-
erine are important because they are central to the body’s “alarm system,” which
causes the fi ght-or-fl ight response (including faster breathing, increased heart rate,
and sweating), which can occur at times of panic. However, the picture is compli-
cated by the fact that panic attacks do not increase levels of stress-related hormones