you feel stressed out, just imagine yourself in this scenario:
You’re walking through the woods 50,000 years ago. As you round
a blind curve on the trail, you come upon a saber-toothed tiger
and her cubs. The tiger growls and crouches, ready to spring.
You freeze in your tracks as the body’s “fight or flight”
response kicks in with the intensity of a punch in the gut: Face
flushed, blood pressure rising, nerve endings crackling, heart
pounding, you leap off the trail and bolt into the forest for
McGaugh, Ph.D., tells the same story, but with a modern twist. A
pioneering researcher in the field of human memory at the
University of California, Irvine, McGaugh and his colleagues
study the links between emotion,
stress hormones, and the brain.
“You come around the corner,”
McGaugh says, “and there’s a California mountain lion, which
tend to eat people out here. Hormones—adrenaline
cortisol—are released from the adrenal gland. These
both will influence the brain. In part they influence a brain
region called the
amygdala. The amygdala is in communication with other
brain regions where memory creation occurs. The amygdala
modulates the process in such a way that if the amygdala is
activated and a memory is in the process of occurring, a
stronger memory is made.”
A popular shorthand term for
the saber-toothed tiger effect that McGaugh describes is
“emotional memory.” The brain has evolved a way to make sure we
remember emotionally arousing experiences. And not just bad
ones: Whether it is the sight of a truck coming right at you on
the highway or meeting the love of your life, emotional
experiences can leave an indelible impression on the mind.
the case of war or other trauma, those memories may be so strong
that they become pathological and bring symptoms of
post-traumatic stress disorder (PTSD). By uncovering
the biochemical mechanisms of how the brain selects emotional
experiences for long-term storage, McGaugh and his colleagues
may have found a way to prevent PTSD.
In Memory Yet Green
What did you eat for breakfast
last Monday? What was the last magazine you read this month? How
many bags of groceries did you bring home the last time you went
shopping? Where were you when you found out that terrorists had
flown planes into the World Trade Center?
The answer to the first three
questions is most likely, “Who cares?” As for the fourth
question, most Americans would probably be able to provide a
vivid recollection of that awful day. Fortunately, our brains
have the ability to filter out unimportant and trivial details.
Otherwise, we would carry around a garbage can of useless
memories. You don’t need to remember such things, and so you
don’t. But if the experience is emotionally potent, it is deemed
worthy of remembrance.
Decades of research on
laboratory animals by McGaugh and many others has revealed the
basic brain mechanisms of emotional memory. Emotional arousal is
a form of stress, and it engages the same systems in the body as
stumbling across a large-toothed predator in the forest. The
body’s fight-or-flight response engages the “stress hormones”
adrenaline and cortisol. Adrenaline activates the amygdala,
which is a signal to the brain that something important has just
occurred. Over time, a stronger and more lasting memory is
created—a process called memory consolidation.
About a decade ago, McGaugh and
colleague Larry Cahill conducted two experiments that vividly
demonstrated the machinery of emotional memory at work. Two
different groups of people were shown a series of 12 images,
each accompanied by a single sentence of narration.
One version of the story was
uneventful and rather boring: A woman and her son visit the
boy’s father at the hospital where he works. On the way, they
witness a disaster preparedness drill featuring a simulated
accident victim. The boy stays with his father and the mother
goes home. End of boring story.
The second group hears a very
different story while being shown the same series of images: On
the way to the hospital, the boy is involved in a car accident
in which his feet are severed. He’s rushed to the hospital,
where surgeons reattach the injured limbs. The boy stays in the
hospital and the mother goes home. Two weeks after hearing these
stories, both groups were tested for their recall of specific
details. The people who viewed the emotionally arousing story
had significantly stronger memories for the emotional parts of
the story and were therefore able to recall more specific
details from the story.
Ultimately, it’s irrelevant
that the emotional content—severely injured child—was negative,
McGaugh emphasizes. “The more activated the amygdala is at the
time learning is occurring, the better the recall will be for
this information.” Had the experience involved eating an
amazingly delicious chocolate cake versus a bland one, the
outcome would have been the same: stronger memory for details
about the delicious cake. “The amygdala is promiscuous as to the
actual experience,” McGaugh says. “It’s just activated by
emotional arousal. It doesn’t have to be a negative emotional
experience. If it’s positive and it engages the amygdala, it
will be a stronger memory.”
It stood to reason that if the
influence of stress hormones on the brain could be blocked, then
the amygdala would not orchestrate stronger memories of
an emotional experience. To test this, Cahill and McGaugh did
another experiment. Two groups of people were told the
emotionally arousing version. Right before hearing the story,
one of the groups was given
propranolol (brand name Inderal), a type of medication
beta-blocker. Widely used to treat heart disease,
beta-blockers interfere with the effects of adrenaline on the
body. In cardiac patients, this results in a slower but more
efficient pumping of the heart. In the study participants, the
drug would prevent stress hormones from activating the amygdala.
The study found that people taking propranolol did not show
stronger memories for the emotional aspects of the story. “They
remembered a lot of what they saw, but they didn’t have a
selectively stronger memory for the emotional content,” McGaugh
The work of Cahill, McGaugh,
and many others reveals something essential about how human
memory works. But it also opens the door to helping people for
whom emotional memory can become a living hell. By one estimate,
up to 15 percent of people who have traumatic emotional
experiences show symptoms of PTSD. Typical signs include
intense, vivid and intrusive flashbacks or nightmares of the
traumatic events, accompanied by extreme anxiety. People with
the syndrome may also become emotionally numb or excessively
jittery and reactive. They may go to great lengths to avoid
reminders of the traumatic events. PTSD can develop after
military combat, rape or other violent assault, natural
disasters such as earthquakes or hurricanes, and automobile
Importantly, PTSD does
not appear, full-blown, immediately after the trauma. It takes a
period of weeks to months for the symptoms to manifest
themselves. It‘s generally believed that a key step in
developing PTSD is repeatedly re-experiencing the event in one’s
mind. Each time, the brain’s emotional memory system kicks in
and strengthens the memory until it is virtually branded on the
person’s consciousness. This period of time represents a
potential window of opportunity for thwarting PTSD.
In a study published in 2002,
Roger Pitman, M.D., a psychiatrist at Harvard Medical School and
expert on PTSD, administered beta-blockers to emergency room
patients within hours of experiencing trauma such as automobile
accidents. The study participants received the drug for a total
of 19 days. One month after the trauma, people on the medication
showed fewer symptoms of PTSD. A similar experiment conducted in
France had the same basic findings.
It’s too soon to start giving
beta-blockers to everybody who experiences trauma. The
medications have potentially harmful side effects, and more
documentation of the benefits and risks is needed before
psychiatrists can launch a full-scale assault on the amygdala.
Pitman is currently planning a larger trial of propranolol at
Massachusetts General Hospital.
One thing is clear: This
research has enormous implications for the scores of people who
each day suffer emotional trauma—whether because of a roadside
bomb in Iraq or a fiery car wreck on the freeway. In addition to
repairing fractured bones and internal injuries, emergency room
physicians may someday be able to write a prescription to
prevent emotional memories from becoming pathological and
"Memory and Emotion: The Making Of Lasting Memories,"
by James L. McGaugh. (Columbia University Press: 2003. 162
Cahill, L., and McGaugh, J.L.,
"A Novel demonstration of enhanced memory
associated with emotional arousal."
(Consciousness and Cognition, 1995, Vol. 4, pp. 410-421.)
"B-adrenergic activation and memory for emotional events,"
by Larry Cahill and others. (Nature, 1994, Vol. 371, pp.
study of secondary prevention of posttraumatic stress disorder
with propranolol," By
Roger K. Pitman and others. (Biological Psychiatry, 2002, Vol.
51, pp. 189-192.)
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