In the case of fear, for example, destroying
an animal’s amygdala has disastrous effects on its
natural alarm system. But that does not make the amygdala
the “fear centre”, because the amygdala also
has connections coming in from and going out to several other
parts of the brain, all of which also are needed to manifest
THE AMYGDALA AND ITS ALLIES
The amygdala is
an almond-shaped structure in the brain; its name comes from
the Greek word for “almond”. As with most other
brain structures, you actually have two amygdalae (shown
in red in the drawing here). Each amygdala is located close
to the hippocampus, in the frontal portion of the temporal
Your amygdalae are essential to your
ability to feel certain emotions and to perceive them in
other people. This includes fear and the many changes that
it causes in the body. If you are being followed at night
by a suspect-looking individual and your heart is pounding,
chances are that your amygdalae are very active!
Source: University of Washington Digital
In certain studies, researchers have directly
stimulated the amygdalae of patients who were undergoing brain
surgery, and asked them to report their impressions. The subjective
experience that these patients reported most often was one of imminent
danger and fear. In studies of the very small number of patients
who have had had only their amygdala destroyed (as the result of
a stroke, for example), they recognized the facial expressions
of every emotion except fear.
In fact, the amygdala seems to modulate all
of our reactions to events that are very important for our survival.
Events that warn us of imminent danger are therefore very important
stimuli for the amygdala, but so are events that signal the presence
of food, sexual partners, rivals, children in distress, and so
Emotions are something
that happens to us much more than something we decide to
make happen. Much of the explanation for this lack of direct
control over our emotions lies in the way that the human
brain is interconnected. Our brains have evolved in such
a way that they have far more connections running from
our emotional systems to our cortex (the locus of conscious
control) than the other way around.
In other words, the noise
of all the heavy traffic on the major highway running
from the limbic system to the cortex masks the quieter
sounds on the little road running in the other direction.
THE TWO PATHWAYS OF FEAR
The amygdala lets us react almost instantaneously to the presence
of a danger. So rapidly that often we startle first, and realize
only afterward what it was that frightened us. How is this possible?
It all has to
start, of course, with a sensory stimulus, such as a
strange shape or a menacing sound. Like all information
captured by the senses, this message must be routed first
to the thalamus. The thalamus then sends this message
on to the appropriate sensory cortex (visual cortex,
auditory cortex, etc.), which evaluates it and assigns
it a meaning. If this meaning is threatening, then the
amygdala is informed and produces the appropriate emotional
But what has been discovered much more recently is
that a part of the message received by the thalamus
is transferred directly to the amygdala, without even
passing through the cortex! It is this second route,
much shorter and therefore much faster, that explains
the rapid reaction of our natural alarm system.
Since everything has a price, this route that short-circuits
the cortex provides only a crude discrimination of potentially
threatening objects. It is the cortex that provides the confirmation,
a few fractions of a second later, as to whether a given object
actually represents a danger. Those fractions of a second could
be fatal if we had not already begun to react to the danger.
And if the cortex
turns out to advise us that there is nothing to worry about
after all, we have merely had a good scare, and that is
have less control over their emotions, because the axons
that send information from the cortex to the limbic system
are not yet fully developed. In addition, the neurons of
the prefrontal cortex that provide much of our rational
control over our emotions do not mature until early adulthood.
In contrast, the amygdala is mature at birth and thus exerts
a heavy influence on children.