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Newsletter of the Infant Mental Health Promotion Project (IMP)
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Volume 21, Summer 1998
QUALITY OF CARE AND THE BUFFERING OF STRESS
PHYSIOLOGY: Its Potential Role in Protecting the Developing
Human Brain
Megan Gunnar, Professor of Child Development, Institute of Child Development, University of Minnesota
One of the most exciting concepts in neuroscience is that of
“neural plasticity” or the capacity of the brain to change with
experience. The evidence now accumulating shows that the blueprint for a brain is not solely contained in our genes, but that
experience is part of the basic information that builds a brain.
disorders such as asthma. Nonetheless, an overactive cortisol
system plays a role in suppression of immunity, and is part of the
mechanism whereby stressful life experiences can literally “make
us sick.”
Effects of Cortisol on Brain Functions
The experiences children have as they enjoy activities, ponder
about the world, engage in interactions, create and challenge
themselves to learn new tasks, provide information for the brain
to decide what connections to make, keep and strengthen and
thus how the brain organizes itself. Along with these positive,
growth-promoting events, there are also stressful events that are
important in sculpting the developing brain. Whether they are
physical (such as pain or physical abuse) or psychological (such
as emotional abuse and neglect), adverse events can be potent
enough to mobilize powerful, stress-sensitive physiological systems.
Like many aspects of physiology, cortisol and its precursor hormones may be “good” in the sense that it helps organize behaviors
that protect us in threatening situations. However, hyperactivation
of this system can have damaging effects. To paraphrase Bob
Sapolsky (1994), cortisol is bad for the brain. What he means is
that if the brain is exposed to high levels of cortisol for prolonged
periods, marked changes in brain activity and in brain structures
may ensue. Multiple brain regions and the brain systems in which
they operate may be affected by chronic or frequent high levels
of cortisol. Examples of the effects on four regions are described
below.
The Stress System
There are two major limbs of the mammalian stress system. One
system regulates catecholamines in the brain and the peripheral
production of adrenaline that increases heart rate, shifts blood
flow to muscles, and breaks down fat stores to make energy available to cells for action.
The other major limb of the stress system is a neuroendocrine
system that produces a hormone called cortisol, which is well
known in its form, cortisone, used as an anti-inflammatory agent.
As cortisol can be obtained from samples of saliva, it has useful
application in finding out more about stress physiology.
Functions of Cortisol
Cortisol and its precursor trophic hormones do many things to
prepare us to withstand threatening or stressful events. Like
adrenaline, cortisol helps to make energy available for action,
but it works more on protein stores than on fat stores. Although
cortisol acts to reduce inflammation, it also has effects on physiology that would seem counterproductive, for example turning
down the efficiency of the immune system. It’s not clear why
nature has given us a system that is activated in threatening situations but also operates to impair our ability to fight disease. One
argument is that it operates as a check on the immune system.
Without an active cortisol system, we are at risk for autoimmune
The structure that appears to be most clearly affected is the hippocampus (see figure 1), a brain region involved in learning
and explicit memory. Explicit memories are memories for specific events, such as the name of the person we just met or where
we left our keys. Elevated levels of cortisol permit or facilitate
events in the brain that cause damage to cells in the hippocampus. Adults who experience post-traumatic stress disorder and
presumably produced high levels of cortisol at the time of the
trauma show shrinkage of the hippocampus. As we age, we
sometimes lose control over regulation of our cortisol system
and often show rising levels of cortisol with each passing year.
We also experience a decrease in memory for specific events
with aging. Interestingly, or disturbingly, these two things are
correlated. Aging adults who experience higher levels of cortisol
also experience the greatest impairments to memory with each
passing year and, with stress, they show large elevations in cortisol which temporarily interfere even more with their ability to
remember specific events.
The hippocampus develops markedly in the first year of life. Babies
don’t remember specific events. What they do remember are
procedures such as how to suck on a nipple, how to shake a
rattle, and the sights, sounds, and smells that are a part of their
“action schemes.” Around their first birthday, they seem to be
developing explicit memories for events and action sequences,
i.e., they can watch someone perform a novel string of actions
and remember that specific action sequence and the objects or
people that were a part of it and repeat short sequences days or
even weeks later.
It is believed that cortisol affects this kind of memory in infants/
toddlers as well as in older people. Babies who have higher stress
hormone or cortisol levels show less electrical activity associated
with the hippocampus than babies with lower cortisol levels. We
don’t know if this means that they remember less of the specific
events, but we do know that babies of this age who show less of
this brain activity remember less of the “action sequences.” So, it
is possible that even in older infants and toddlers, memories for
specific events may be laid down differently when cortisol levels
are higher.
The anterior cingulate gyrus (see figure 1) plays an important
role when we have to selectively pay attention to something important while ignoring other things that we are pulled to do.
Inhibiting our reach for a candy or another child’s toy or an action said by Simon without “Simon says” as its preamble, all
require activity in this area of the brain. Selectively attending to
information and stopping ourselves from doing things we are
pulled to do is a competence that develops slowly from
toddlerhood. This kind of effortful control is also something that
we can lose as we grow old. Older people who have increasing
levels of cortisol with each passing year can become disoriented
and have trouble focusing attention and inhibiting “inappropriate” actions. These problems, like their problems with explicit
memory, increase markedly when they are stressed and cortisol
levels rise even further.
My colleagues and I have studied the links between cortisol and
effortful control in preschool children. Children whose parents
and teachers tell us are consistently less controlled than their
peers are the ones we find showing consistently high levels of
cortisol in familiar classroom settings. Of course, we don’t know
whether their chronically higher cortisol levels make it hard for
their brains to perform effortful control, or whether their lack of
control gets them into situations that are stressful. We suspect
that both may be involved.
Cortisol also has an effect on the amygdala (see figure 1), an
area of the brain involved in processing negative events. The
amygdala is involved in triggering elevations in adrenaline and
cortisol to negative emotional stimuli. High levels of cortisol, when
they occur frequently, lower the threshold for activation of the
amygdala and may result in an individual becoming more sensitive to negative emotions and more likely to produce a hormonal
stress reaction when threatened.
All of these three brain regions interact with an area of the prefrontal cortex (see figure 1) that is sensitive to information about
the social environment and social partners. Poor development
and functioning of these regions may make it especially difficult
for children to act appropriately in social situations and may underlie some of the problems that some children have with peers
and adults.
In summary, it appears that frequent, high, levels of cortisol could
be doing three things, at least, to the developing brain:
1) interfering with memory and learning
2) interfering with the development of attention regulation and
self control,
3) lowering the threshold for experiencing negative emotions
and activating stress systems.
These problems may appear especially marked in social situations.
Cortisol is not the only mechanism that may be involved in translating chronically stressful or chaotic life histories into the
behavioral and emotional problems described above, but failure
to regulate cortisol responses during early development may play
an important role in shaping a brain that is less capable of learning, attention regulation, self-control, and modulated response
to mild threats and challenges. It is important to note that these
predictions are hypotheses that have not yet been proven in humans.
Protecting Infants from Stress
Does this mean that we need to protect infants and young children from ever getting upset? Do we need to shield them from
falling down, getting scared, being challenged? Do we have to
raise them in a bubble so that they never experience elevations
in cortisol? This would not seem to be a recipe for developing a
stress resilient child. From behavioral research we know that children who have no experiences with anything bad, sad, or scary
are not very well prepared to handle life’s challenges. How have
we evolved to learn how to manage threat while not having our
brains potentially affected by stress hormones? Studies of infant
rats may provide a clue.
Figure 1 — Section through the brain
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The infant rat starts life with a very reactive stress system. But,
within a few days, it becomes difficult to elevate cortisol-like stress
hormones in the baby rat, and this buffered cortisol system remains in place until about the time the baby (now a juvenile)
begins to leave the nest on a regular basis. What allows the baby
rats system to stay so hypo-responsive? Studies have shown that
it is specific cues the baby receives from the mother rat’s
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caregiving: milk in the mouth and vigorous maternal licking and
grooming. Some mother rats are really good caregivers, while
others have less well-organized maternal behavior. Offspring of
well-organized mother rats grow up with well-organized stress
systems: they are less fearful, produce shorter and better organized cortisol-like stress responses, and show other brain chemistry that is associated with competent rat behavior. Offspring of
less well-organized mothers show the opposite effects. Stressing
the mother rat is one way to disrupt her mothering and cause her
offspring to become stress vulnerable in adulthood.
Have we humans evolved in the same way as rats, so that early
mothering or nurturing tells our stress hormone systems that they
can stay quiet even when we find things somewhat painful, scary
or threatening?
Like the baby rat, human newborns have very reactive and labile
stress systems. Almost any stimulation, even undressing and
weighing a baby will produce increases in cortisol. To find our
how this changes over time, we studied babies while they underwent their well-baby checkups and immunizations. We learned
that at two months babies show a big cortisol reaction, just like in
the newborn period. But by four months and six months their
reaction is less, and by 15 months, the checkup and shots don’t
budge the cortisol. This is not because 15-month-olds love getting shots. In fact, they cry more at 15 months than they do at
six months. What has changed is that at 15 months they sometimes begin to cry before they get the shot and they struggle to
escape the nurse’s grasp and reach their protective or secure
base. They have formed specific attachments and they seek those
people they are attached to for protection and comfort.
Like the rat, if the quality of care the baby has received is less
sensitive and responsive, do we see that the buffer provided by
the attachment relationship is “leaky?” To answer that question
we tested 18 month olds with a series of strange events (such as
weird puppets that suddenly pop out of the wall or a clown suddenly appearing). Many of the children seemed wary and a bit
scared of the puppets or clown that has come to play with them.
A week later we tested the same toddlers in the Ainsworth Strange
Situation to measure the security of their attachment relationship with the person who was with them in our “scary” session.
If a child was fearful with our scary events, but was securely attached to the parent who was with them, their cortisol levels did
not rise. But if they were fearful or wary and insecurely attached
to that parent, there was a significant increase in cortisol. This
finding has now been replicated in our laboratory and in other
laboratories around the world. In addition, we and others have
examined children in attachment relationships that are described
as not only insecure, but also disorganized and disoriented. These
relationships tend to be seen when the child has been abused by
the attachment figure or when that person has been clinically
depressed for significant periods during the child’s infancy. Cortisol levels for these children tend to be higher than for other
children.
So, like the rat, our cortisol system seems to be buffered by the
availability of a mothering figure when we are babies and it seems
Newsletter of the Infant Mental
Health Promotion Project
to become leaky when the quality of care is disrupted. When
things get bad enough to result in disorganized/disoriented attachment, cortisol levels may be tonically or more consistently
higher. What happens when children have no one with whom to
form an attachment relationship?
Romanian Orphanage Children
Children in Romanian orphanages have provided an opportunity to study what happens when babies are severely deprived of
loving, warm and responsive care. These children suffer from
many aspects of institutional rearing that results in stunted physical growth of the type seen in emotionally and physically neglected children and immense delays in their motor, cognitive
and social development. We were interested in whether this deprivation also affected their cortisol system. The work on baby
monkeys reared on surrogate cloth mothers (the Harlow-type
monkeys) would suggest it should. These monkeys are known to
be much more stress reactive as adults. Along with Steve Suomi
and his colleagues, we studied the cortisol levels produced by
these monkeys over the course of normal days in the nursery. A
normal daily pattern for cortisol is one of high levels just before
waking and then a rapid drop in the first hour or two and a
gradual decrease over the rest of the day until there is almost no
cortisol by the time we go to sleep at night.
The pattern in the surrogate reared monkeys is different. They
show a peak in cortisol late in the morning! We reasoned that
this was because, although they could cling to their surrogate
mothers if there was a disturbance in the nursery, the surrogate
was a poor buffer of the cortisol system and, therefore, any disturbance might elevate their cortisol levels. To test this we varied
the amount of disturbance in the nursery and saw something that
looked more like the normal daily rhythm if disturbance was eliminated in the morning. Children reared in the orphanage show a
similar pattern of a rising cortisol level over the morning hours.
We can’t prove that the cortisol is doing anything to their brains,
but we do know that the noon levels were higher for orphans
who were more developmentally delayed and physically stunted.
Implications
The data described above does not prove that our cortisol stress
systems are affected by early care experiences. But, they are
consistent with the idea that having a good, secure, buffering
relationship may shape a more stress resilient child, while having
an insecure relationship, particularly if it is aberrant, or having
no one to use as a buffer, may shape a more stress vulnerable
child. Is early experience destiny?
If we receive the kind of care that provides a good buffer are we
forever protected from developing a hyper-reactive stress system? This seems unlikely, as horrific traumatic experiences later
in life are capable of producing post-traumatic stress disorders in
most people. On the other hand, if our quality of care provided a
leaky buffer (such as when children are reared in depriving orphanage conditions or by neglecting or abusive caregivers) will
we necessarily grow up with a more reactive, vulnerable, stress
system? How much can early effects on our stress systems be
altered, for better or worse, by later experiences? How plastic or
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changeable do these systems remain throughout childhood? Are
there critical or sensitive periods that leave a lasting legacy on
our brain’s stress systems? These, of course, are the central questions for our field. The hope that these systems remain malleable
guides many of our intervention efforts. The belief that it is better
to prevent a problem than to fix one is what motivates us to
reach children and families as early as possible to help parents
provide the safe and secure buffering system that we believe fosters healthy infant and child development.
the brain community is to ask questions relevant to early intervention and provide answers that can be used to improve the life
course of children. Brain scientists and behaviour scientists and
practitioners speak different languages. Learning each other’s
language and a bit about each other’s culture is essential if we are
to communicate. It is hoped that as practitioners learn more from
the brain community, they will challenge that community with
questions that are relevant to early intervention efforts. z
References
The new era of brain science supports many views of development derived from observing children’s behavior. Knowledge about
brain development is relevant to early intervention and new techniques and strategies for helping challenged brains are being
developed through this knowledge. However, the new science is
still in its infancy. More ideas that have implications for early
intervention are likely to come from this work in the near future.
To be effective, however, the “brain” community needs to understand more from the “behaviour” community. This is essential if
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Sapolsky R (1994). Why zebras don’t get ulcers: A guide to stress,
stress related diseases and coping. New York: Freeman and Co.
Suggested Reading
Small MF (1998). Our Babies Ourselves: How biology and culture shape
the way we parent. Anchor Books, NY $34.95 (Available from
Parentbooks, 201 Harbord St. Toronto, ON M5S 1H6 (416) 537-8138
FAX 537-9499)
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Newsletter of the Infant Mental
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