In this Spotlight feature, we will
explain the biology of fear: why it has evolved, what happens in our bodies
when we are scared, and why it sometimes gets out of control. Scroll down...if
you dare.
What is fear, and how can it feel both good
and bad?
Everyone can get scared; fear is an
unavoidable facet of the human experience.
People generally consider fear as an
unpleasant emotion, but some go out of their way to trigger it — such as by
jumping out of planes or watching scary movies.
Fear is justifiable; for instance,
hearing footsteps inside your house when you know that you are the only one
home is a valid reason to be terrified.
Fear can also be inappropriate; for
example, we might experience a rush of terror while watching a slasher movie,
even though we know the monster is an actor in makeup and that the blood is not
real.
Many individuals consider phobias as the most
inappropriate manifestation of fear. They can attach themselves to pretty much
anything — such as spiders, clowns, paper, or carpets — and significantly
impact people's lives.
Why do we
get scared?
As far as evolution is concerned,
fear is ancient and, to a certain extent, we can thank fear for our success as
a species. Any creature that doesn't run and hide from bigger animals or
dangerous situations is likely to be removed from the gene pool before it's
given the chance to procreate.
Fear's
essential role in survival helps explain why it sometimes seems a little
trigger-happy.
In other words, it makes sense to be
a little jumpy if you're an animal in a hostile environment. It's better to run
and hide when your own shadow catches you by surprise than to presume that a
shadow is safe, only to be eaten by a bear 5 seconds later.
What
happens in the body?
People often refer to the
physiological changes that occur when experiencing fear as the fight-or-flight
response. Overall, as the name suggests, the changes prepare the animal to
either fight or run.
Breathing rate increases, heart rate
follows suit, peripheral blood vessels (in the skin, for instance) constrict,
central blood vessels around vital organs dilate to flood them with oxygen and
nutrients, and muscles are pumped with blood, ready to react.
Muscles —
including those at the base of each hair — also become tighter, causing
piloerection, which is colloquially called goosebumps. When a human's hair
stands on end, it doesn't make much of a difference to their appearance, but
for more hirsute animals, it makes them seem larger and more formidable.
Metabolically, levels of glucose in
the blood spike, providing a ready store of energy if the need for action
arises. Similarly, levels of calcium and
white blood cells in the bloodstream see an increase.
Triggering
the response
The fight-or-flight response begins
in the amygdala, which is an almond-shaped bundle of neurons that forms part of
the limbic system. It plays an important role in the processing of emotions,
including fear.
When we are afraid, it sets off a
sophisticated, coordinated response in our brains and bodies.
The amygdala is able to trigger
activity in the hypothalamus, which activates the pituitary gland, which is
where the nervous system meets the endocrine (hormone) system.
The pituitary gland secretes
adrenocorticotropic (ACTH) hormone into the blood.
At this time, the sympathetic
nervous system — a division of the nervous system responsible for the
fight-or-flight response — gives the adrenal gland a nudge, encouraging it to
squirt a dose of epinephrine into the bloodstream.
The body also releases cortisol in
response to ACTH, which brings about the rise in blood pressure, blood
sugar, and white blood cells. Circulating cortisol turns fatty acids into
energy, ready for the muscles to use, should the need arise.
Catecholamine hormones, including
epinephrine and norepinephrine, prepare muscles for violent action.
These hormones can also: boost
activity in the heart and lungs; reduce activity in the stomach and intestines,
which explains the feeling of "butterflies" in the stomach; inhibit
the production of tears and salivation, explaining the dry mouth that comes
with a fright; dilate the pupils; and produce tunnel vision and reduce hearing.
The hippocampus, which is a brain
region that is dedicated to memory storage, helps control the fear response.
Along with the prefrontal cortex, which is part of the brain involved in
high-level decision-making, these centers assess the threat.
They help
us understand whether our fear response is real and justified, or whether we
might have overreacted somewhat.
If the hippocampus and prefrontal
cortex decide that the fear response is exaggerated, they can dial it back and
dampen the amygdala's activity. This partly explains why people enjoy watching
scary movies; their sensible "thinking brain" can overpower the
primal parts of the brain's automated fear response.
So, we get to experience the rush of
fear before our more reasonable brain centers dampen it down.
Why do we
freeze when we're scared?
The idea of our bodies preparing to
fight or fly makes good sense from a survival standpoint — but how would
freezing be of any use? An animal that simply stands rooted to the spot would
make an easy snack for a predator, you might think.
When they are frightened, most
animals freeze for a few moments before they decide what to do next. Sometimes,
staying motionless is the best plan; for instance, if you are a small mammal or
if you are well-camouflaged, staying still could save your life.
A 2014 study
identified the neurological root of the freezing response. It is generated by
cross-talk between the periaqueductal gray (PAG) and the cerebellum. The PAG
receives various types of sensory information about threats, including pain
fibers. The cerebellum is also sent sensory information, which it uses to help
coordinate movement.
The
researchers found a bundle of fibers that connect one region of the cerebellum,
called the pyramis, directly to the PAG. Messages that run along these paths
cause an animal to freeze with fright.
The authors of the study hope that
their findings might one day help design ways to treat people with anxiety disorders
and phobias who can become paralyzed with fear.
The
question of phobias
Medical professionals class phobias
as an anxiety disorder. As mentioned earlier, they are often an irrational and
overactive fear of something that, most often, cannot cause harm. They can
attach to pretty much anything and significantly impact people's lives.
Fear of the number 13 is called
triskaidekaphobia.
There is no hard and fast reason why
a phobia will develop; both genes and the environmentcan be involved.
Sometimes, the origin can be
relatively easy to understand: someone who witnesses someone falling off a
bridge might later develop a phobia of bridges.
In general, though, a phobia's
origins are tricky to unravel — after all, most people who witness someone
falling off a bridge do not develop a phobia of bridges, so there is more to it
than simple experience.
While there are still many questions
left unanswered, scientists have uncovered some of the neural events that
underpin phobias.
Given our understanding of the
amygdala's involvement in the fear response, it is unsurprising that phobias
are linked to heightened activity in this region.
One study also
discovered that there was a disconnect between the amygdala and the prefrontal
cortex, which normally helps an individual override or minimize the fear
response.
Aside from the fear felt when
someone with a phobia meets their nemesis, these individuals are also in a
heightened state of arousal; they always expect to see their trigger, even in
situations where it is not particularly likely to appear.
Some researchers argue that this
vivid, fearful expectation plays a significant part in boosting the fear
response when they do come across their phobic object.
Another study explored this phenomenon in people with
arachnophobia. It found that if scientists told these individuals that
they might encounter
a spider, activity in their brains differed from control participants without a
phobia.
Activity
in the lateral prefrontal cortex, precuneus, and visual cortex was
comparatively lower.
The authors say that these brain
regions are key for the regulation of emotions; they help keep us level-headed.
A reduction in their activity suggests a reduced ability to keep a lid on
fearful emotions.
Often, an individual with a phobia
will be well aware that their response to the object that they fear is
irrational. The weaker activity in these brain areas helps explain why this
might be; the parts of the brain responsible for keeping a cool head and
assessing the situation are muted, thereby allowing more emotional regions to
play their hand.
The
takeaway
The fear response has kept us alive.
It is primal, and we should respect it. At the same time, it can be unpleasant
and interfere with people's day-to-day functioning. However, paradoxically,
fear is also the source of a highly enjoyable adrenaline rush.
Fear inspires filmmakers, roller
coaster designers, psychologists, neuroscientists, and everyone in-between. It
is a fascinating and multifaceted human emotion.
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