Humans and other animals seem hard-wired to develop fear of noxious or dangerous stimuli.
Fear is an unpleasant and often strong emotion caused by anticipation or awareness of danger. Fear is completely
natural and helps people to recognize and respond to dangerous situations and threats.
Humans have a complex emotional learning to detect danger and activate brain alarm systems.
However, alarm systems can presumably also be disordered. Healthy fear -- or
fear which has a protective function -- can evolve into unhealthy or pathological fear,
which can lead to exaggerated behavior.
Such fears appear characteristic of anxiety disorders, particularly specific phobia.
A phobia is an intense, unrealistic fear, which can interfere with the ability to socialize,
work, or go about everyday life, that is brought on by an object, event or situation.
How phobia is created?
Fear provoked by aversive stimulus triggers an emotional reflex. This is because stress and trauma are stored
as memories in certain parts of the brain (see below). This storage is
called "fear conditioning", and is how a phobia is created.
Fear conditioning is the method by which organisms learn to fear new stimuli. It is a form of learning in which fear
is associated with a particular neutral context (e.g., a room) or neutral stimulus (e.g., a tone). This can be done by
pairing the neutral stimulus with an aversive stimulus (e.g., a shock, loud noise,
or unpleasant odor). Eventually, the neutral stimulus alone can elicit the state of fear.
The seat of fear
Fear conditioning, emotional expression, memory storage and recall are controlled by limbic system which is made up of
a number of structures such as amygdala and thalamus (2).
Fear seems to send nerve impulses
along the pathway from the ear to the thalamus and either directly to the amygdala or, more desirably, into the auditory portion of the
sensory cortex, where they can be analysed before being sent to the amygdala. When the amygdala receives nerve signals indicating a threat,
it sends out signals that trigger such reactions as rapid heartbeat and raised blood pressure.
Fig. 1 - fMRI activation of the right amigdala in response to a fear situation.
It is notable, for example, that social anxiety
disorder is characterized by increased amygdala activation, and psychopathy by decreased amygdala activation,
during an aversive conditioning task (Figure 1) (2). There may be attenuated responses in such regions after
Below we ilustrated one kind of phobia.
Acrophobia, or the fear of heights, is characterized by an irrational fear of height situations resulting in the
avoidance of such situations or the confrontation of such situations with marked distress. This fear for some is endured with distress,
whereas for others the fear is so intense that height situations must be avoided altogether. Some may not be able to see a physician if
his office is on the fifth floor, will not take a job because the office is on the tenth floor, or will not visit friends that move into
an apartment three stories up.
Vídeo 1: Illustrating fear of heights in a funny matter.
Over the past several decades, psychologists and other researchers have developed
some effective behavioral and pharmacological treatments for phobia, as well as technological interventions.
Fear extinction involves repeated exposure to a fearful memory or object,
in the absence of adverse consequences.
Behavioral therapy to phobia has included exposing the subject to anxiety-producing
stimuli while allowing this anxiety to attenuate. In vivo graded exposure is a common and
effective treatment for phobia. For example, if a patient is afraid of heights, therapy sessions
might begin by having the patient look through a third floor window with the therapist present.
In subsequent sessions, the patient might move up to a window on the tenth floor. Other common
locations for in vivo therapy are outside stairways, balconies, bridges, and elevators.
A person with a phobia may appear to be cured after behavioural treatment only
to have the phobia return during an episode of high stress. Why does it happen? Joseph LeDoux, Ph.D., a
neuroscientist at New York University, suggests
that this is because the signal pathways from the thalamus to the
amygdala and sensory cortex have been normalized, but the internal circuits in the amygdala have not (2). One reason for the difficulty in
exerting conscious control over fear could be because there are far more cell circuits leading from the amygdala to the prefrontal cortex,
the area of the brain most responsible for reasoning, than there circuits going the other direction.
Using virtual reality to treat phobia
Phobias, such as acrophobia, can also be treated with the use of virtual reality exposure therapy. After relaxation training and discussion about
what situations produce anxiety, the client is exposed to progressively higher anxiety virtual environments. These may include a virtual
construction elevator, hotel elevators. As the client progresses, stimuli such as wind, vibration and sound can be added to create further
Fig. 2 - Session of virtual reality. Client is exposed to progressively higher anxiety virtual environments.