390 Chapter 11 Psychological Disorders
or prisoners. As in the studies of the hippocampus
that we just described, exposure to combat was
necessary for the onset of PTSD, but not suf-
ficient. Among veterans who scored high on all
three factors, though, fully 97 percent developed
PTSD—and the strongest independent predictor
was having inflicted harm on prisoners or civil-
ians (Dohrenwend et al., 2013). Obviously, most
soldiers do not feel guilty or remorseful for carry-
ing out orders in war; but those who do, as was the
case for many veterans of Vietnam and Iraq, may
come home with an added burden of PTSD.
In sum, many cases of persistent PTSD may
result from cognitive and neurological vulner-
abilities that existed before the trauma took place,
combined with undergoing a horrific experience
for which one feels responsible or guilty, making it
more likely that the trauma will trigger persistent
symptoms.Obsessive-Compulsive and Related Dis-
orders. Obsessive-compulsive disorder (OCD) is
characterized by recurrent, persistent, unwished-
for thoughts or images (obsessions) and by repetitive,
ritualized behaviors that the person feels must
be carried out to avoid disaster (compulsions). Of
course, many people have trivial compulsions and
practice superstitious rituals. Baseball players are
famous for them; one won’t change his socks and
another insists on eating chicken every day while
he is on a hitting streak. Obsessions and compul-
sions become a disorder when they become uncon-
trollable, time consuming (taking up an hour or
more a day), and interfere with a person’s life.
People who have obsessive thoughts often find
them frightening or repugnant: thoughts of killing
a child, of becoming contaminated by a handshake,obsessive-compulsive
disorder (OCD) A dis-
order in which a person
feels trapped in repeti-
tive, persistent thoughts
(obsessions) and repeti-
tive, ritualized behaviors
(compulsions).
attack; such symptoms usually subside over time.
But in 1980, the third edition of the DSM intro-
duced the diagnosis of posttraumatic stress disorder
(PTSD) in response to ongoing concerns about the
severe psychiatric toll on veterans of the Vietnam
War. These soldiers were having symptoms for
years after they returned home: recurrent, intru-
sive thoughts about the trauma; recurrent night-
mares; flashbacks; avoidance of anyone or anything
that aroused distressing memories; and increased
physiological arousal, reflected in insomnia, irrita-
bility, and impaired concentration.
As researchers began studying this disorder,
they encountered a puzzle: Most people who live
through a traumatic experience eventually recover
without developing long-lasting PTSD (Bonanno
et al., 2010). Why, then, do others continue to have
symptoms for years, sometimes for decades? One
answer is that many of these individuals have a pre-
existing vulnerability. Behavioral-genetic studies of
twins in the general population and among combat
veterans have found that some people are geneti-
cally more vulnerable than others to developing
PTSD (Stein et al., 2002; Wilker & Kolassa, 2013;
Yehuda et al., 2009). Other studies have found
that people who develop PTSD often have a prior
history of psychological problems, such as anxi-
ety and impulsive aggression. And some lack the
social, psychological, and neurological resources
to avoid having preventable traumatic experiences
in the first place or to cope with unavoidable ones
(Breslau, Lucia, & Alvarado, 2006).
Another preexisting factor is the size of the
hippocampus, which is crucially involved in auto-
biographical memory. In many PTSD sufferers,
the hippocampus is smaller than average (McNally,
2003). An abnormally small hippocampus may fig-
ure in the difficulty of some trauma survivors to
react to their memories as events from their past,
causing them to keep reliving those memories in the
present (Wilker & Kolassa, 2013). An MRI study
of identical twins, only one of whom in each pair
had been in combat in Vietnam, showed that the
veterans who developed chronic PTSD had served
in combat and had a smaller hippocampus than nor-
mal. Twins who had smaller hippocampi but no mil-
itary service did not develop PTSD, and neither did
the twins who did experience combat but who had
normal-sized hippocampi (Gilbertson et al., 2002).
In the case of war-related PTSD, however,
another contributing factor is experiential, not
biological: directly inflicting harm on civilians or
prisoners. An in-depth study of 260 male veterans
from the National Vietnam Veterans Readjustment
study examined the role of three factors: combat
exposure, prewar vulnerability, and the vet’s per-
sonal involvement in harming or killing civiliansposttraumatic stress
disorder (PTSD) An
anxiety disorder in which
a person who has expe-
rienced a traumatic or
life-threatening event
has long-lasting symp-
toms such as recurrent,
intrusive thoughts, flash-
backs, nightmares, and
increased physiological
arousal.
This grief-stricken soldier has just learned that the body
bag on the flight with him contains the remains of a
close friend who was killed in action. Understandably,
many soldiers suffer posttraumatic stress symptoms. But
why do most eventually recover, whereas others have
PTSD for many years?