Fear
and Loathing in the Human Brain
by Dr Andy Calder
Research
addressing the brain regions involved in human emotion
has expanded
rapidly in recent years. This is, in part, due to the
widening availability of new brain imaging technology,
but also to a newfound interest in the idea that certain
individual emotions may be served by separate brain
systems. This latter theoretical position is at the
heart of the idea that selected sets of so-called "basic" emotions
with strong evolutionary histories constitute the foundations
of human emotion. Although this concept has its origins
in the work of Charles Darwin, it only really took
off following the work of psychologists such as Silvan
Tomkins, Paul Ekman, and Carol Izard in the 1960s
and 70s. Prior to this, emotion research
was dominated by the idea that all emotions were coded
as values on a limited number of dimensions or scales
coding more general emotional constructs, such as valence
(how positive or negative an emotion is) and arousal
(whether the emotion is associated with low arousal
or high arousal). Similarly, early neurological accounts
of emotion processing took a similar all-encompassing
approach in which all emotions were processed by a
circuit of interconnected brain structures known as
the limbic system.
Two important findings of
Ekman and his contemporaries that changed theories
of emotion were studies demonstrating
that certain emotions (happiness, sadness, anger, fear,
and disgust) were associated with distinct facial signals,
and that these were common to cultures throughout the
world; observations that now constitute two of the
defining features of basic emotions. A third posited
feature was
the idea that each basic emotion should be associated
with a distinct (neuro)physiological signature, such
as a particular brain circuit or a more peripheral
body state response, including heart rate, or galvanic
skin response (an
index of lying in the famous lie detector test) and
so on. Human evidence consistent with this
third feature proved difficult to find; However, support
was found in non-human biological studies by researchers
such as Joe LeDoux and Jaak Panksepp.
It is of considerable
interest, then, that work with humans over the last
eight years has begun to identify that certain emotions
may
be coded by partially distinct brain systems as Ekman
and his colleagues had predicted. This research has
been aided greatly by recent advances in brain imaging
technology
that allows more precise localisation of the regions
damaged in brain-injured patients, and identification
of the
areas of the brain that are activated in healthy
individuals when they perform a psychological task.
A large number
of these studies have addressed the areas of our
brain that are used to recognise emotion in others;
in other
words brain systems involved in recognising facial
and vocal signals of emotion. Two emotions that have
received
considerable amount of attention are fear and disgust.
To date brain imaging technology
and work with patients who have suffered brain injuries
has shown that a small almond-shaped structure in the
brain called the amygdala, plays a significant role
in recognising facial and vocal expressions of fear.
For example, my colleagues and I at Cambridge University
studied a lady known as DR who underwent neurosurgery
to relieve epilepsy that was resistant to pharmacological
treatment. The cause of DR's epilepsy was her left and
right amygdala, and the surgeon removed both structures
in an attempt to reduce the frequency of her epileptic
fits. Calder and colleagues demonstrated that DR showed
an impaired ability to recognise fear, and to a lesser
extent anger from facial and vocal expressions of emotion,
whereas her recognition of other emotional expressions
was normal. This showed that amygdala was important
for recognising these emotions.
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