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The Rattled Cage
We might reasonably intuit that some types of childhood adversity are more
damaging to us than others. For instance, we’d expect that the trauma that Kat
experienced in knowing that her father murdered her mother would have a
dramatically worse biological impact on her than Laura’s having been
chronically put down by her depressive mom.
We’d certainly assume that Kat’s story would be more biologically damaging
than that of Ellie, who was the second youngest of five children and grew up in a
quiet suburban neighborhood outside Philadelphia. Ellie remembers having a
very close relationship with her parents, but, as she got older, she says, “I knew
something wasn’t right. My two oldest brothers were time bombs of violent
emotion, just waiting to go off. Sitting at the dinner table with my parents,
talking about politics, they’d start fighting each other over nothing at all—and
the fights got ugly.”
Soon the boys were getting into trouble with alcohol and drugs—“and the
police started showing up.” Ellie recalls, “I’d often hear my parents and my
brothers screaming at each other at two in the morning. My mom and dad would
come in my room and tell my little sister and me not to be scared, that
everything was okay, but it was terrifying,” especially when her older brother
ended up in jail.
Ellie got good grades, despite the stressors at home, and went to college in
California on an athletic scholarship. But, after college, she began having
suicidal thoughts and, at age twenty-four, was diagnosed with severe
autoimmune psoriasis. “My body was attacking itself,” she says.
According to ACE research, growing up with a family member who is in jail
is related to a much higher risk of poor health-related outcomes as an adult.
Laura, John, Georgia, Kat, Michele, and Ellie tell six unique stories of childhood
adversity. And yet their brains reacted to these different levels of trauma in a
similar biological way. The developing brain reacts to different types and
degrees of trauma so similarly because all the categories of Adverse Childhood
Experience stressors have a very simple common denominator: they are all
unpredictable. The child can’t predict exactly when, why, or from where the next
emotional or physical hit is coming.
Researchers refer to stress that happens in unpredictable ways and at
unpredictable times as “chronic unpredictable stress,” and they have been
studying its effects on animal development for decades—long before Felitti and
Anda’s investigation into ACEs first began. In classic studies, investigators
expose animals to different types of stressors for several weeks, to see how those
stressful stimuli affect their behavior. In one experiment, McCarthy and her
postdocs exposed male and female rats to three weeks of chronic unpredictable
mild stress. Every day, rats were exposed to a few low-grade stressors: their cage
was rotated; they were given a five-minute swim, their bedding was dampened;
they went for a day without food; they were physically restrained for thirty
minutes; or they were exposed to thirty minutes of strobe lights.
At the end of the three weeks, McCarthy’s team examined the rats to evaluate
brain differences. In the group exposed to chronic unpredictable mild stress, she
and her team found significant changes in the receptors in the brain’s
hippocampus—an area of the brain associated with emotion, which would
normally help modulate stress hormone production and put the brakes on
feelings of stress and anxiety after a stressor has passed.
The rats who’d been exposed to chronic unpredictable stress weren’t able to
turn off the stress response, but the control group that experienced no stress
showed no brain changes.
However, when stress is completely predictable, even if it is more traumatic—
such as giving a rat a regularly scheduled foot shock accompanied by a sharp,
loud sound—the stress does not create these exact same brain changes. “Rats
exposed to a much more traumatic stressor get used to it if it happens at the same
time and in the same way every day,” says McCarthy. “They manage. They
know it’s coming, then it’s over.” Moreover, she says, “They don’t show signs
of these same brain changes, or inflammation, or illness.”
On the other hand, she adds, “if you introduce more moderate but
unpredictable stressful experiences at a different time each day, with different
levels of intensity, adding in different noises, such as loud clapping at
unpredictable intervals, those rats show significant changes to the brain. And
they get physically sick; they get ulcers.”
This is why researchers believe that it is the unpredictability of stress that is
particularly damaging. On a walking tour of her lab, McCarthy points out the
metal stand on which rodents’ cages can be gently shaken for a short time.
“Even the most mild unpredictable stressors, something as simple as gently
shaking the cage, playing rock music, putting a new object in the cage that they
aren’t used to, all these cause very specific changes in the brain when we do
them without warning.”
The bottom line, McCarthy says, is that the brain can “tolerate severely
stressful events if they are predictable, but you cannot tolerate even mild
stressful events if they are very unpredictable.”
Yet even though researchers have known for years about the effects of chronic
unpredictable stress on the adult brain, only recently have they examined what
happens to the brains of children exposed to chronic unpredictable stressors.
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