Survival of the cowardly
From New
Scientist, 4 January
1997
The Emotional Brain: The Mysterious
Underpinnings of Emotional Life by Joseph LeDoux, Simon
& Schuster, $25, ISBN 0 684 80382 8
EMOTIONS are not all the same. Several
of them--including happiness, love, sadness, fear and anger--probably
evolved to serve particular purposes. Love in mammals, for
instance, is likely to have grown out of the system of infant
attachment to parents. Fear is part of a defence system
that helps animals to meet dangers, including threats from
other individuals of the same or different species, and
has been part of the equipment of most animals since the
evolutionary appearance of the reptiles.
The subtitle of
Joseph LeDoux's The Emotional Brain is "The mysterious
underpinnings of emotional life". LeDoux is right: the brain
mechanisms behind emotion are still mysterious. Strange
emotional consequences of brain damage have been described,
mood changes are prod![]()
uced by a variety of drugs,
and plenty of anatomical pathways have been identified.
But there has been no theory that integrates these diverse
observations.
LeDoux, a neuroscientist,
has changed this. He is a professor at the Center for Neural
Science at New York University. His investigations of the
links between the brain's structure and emotions have helped
to give this field scientific respectability. Psychologists
had for years speculated about the links between brain and
emotion. LeDoux's experimental approach has shown that emotion
can occur without cognitive processing in the cortex.
LeDoux's research,
using an array of neurobiological methods, centres on the
amygdala, a small area hidden within the temporal region
of the brain. In humans, the amygdala is the size and shape
of an almond (amygdalum is Latin for almond). According
to LeDoux's evidence, this area is the heart of the emotion
system. It is "able to process the emotional significance
of individual stimuli as well as complex situations. The
amygdala is, in essence, involved in the appraisal of emotional
meaning". Appraisal--the comparison of an event to a person's
goals and resources--is the process that cognitive researchers
agree is the key to how particular emotions are produced
in response to particular kinds of events.
According to LeDoux,
we can learn some general principles of emotions by studying
fear. In evolutionary terms, "fearless" animals would have
been less likely to survive. In humans, fear remains valuable,
though sometimes we seem to pay an unduly high price through
our potential for shyness, loss of self-confidence, and
disabling anxiety disorders.
LeDoux explains
how he came to his idea of the emotional importance of the
amygdala while studying learned fear responses in animals.
When an animal is frightened, it exhibits characteristic
changes that include remaining motionless (freezing), raised
blood pressure, increased heart rate and the release of
stress hormones into the bloodstream. In learned fear, it
is the context of a threatening situation that is learned.
LeDoux gives an example: someone runs up to you on the street
and mugs you. Next time you see someone running towards
you, the fear response is likely to be triggered again,
now in anticipation. The fear response has been learned
by a process called classical conditioning, mediated by
the amygdala.
Why has this response
been so important in the course of mammalian evolution?
Predators are alert to any visual movement, and to the slightest
sound. Remaining motionless has therefore, on average, given
potential prey the best chance of escaping detection and
surviving. Even if a predator does detect a fearful animal,
the animal's increased heart rate and hormonal changes have
prepared its body for escape, flight, or a last desperate
onslaught against the attacker. Animals have also benefited
from avoiding anything with a context that is even vaguely
similar to threats that have occurred previously. Because
the categorisation of fear-provoking contexts is vague,
mistakes are common. But the price of making mistakes has
been small in evolutionary terms compared with the mortal
consequences of not reacting immediately. The response remains
of value in humans, because thinking takes too long. The
emergency response maximises the chance of achieving safety
without having to think.
Having explained
how the defensive system works, LeDoux considers the relation
of fear to learning. He quotes an observation on a patient
made by the Swiss psychologist Édouard Claparède
at the beginning of the century. The patient had suffered
brain damage and seemed unable to form new memories. Every
time Claparède interviewed her she had no recollection
of having seen him before. So he would always reintroduce
himself and, in doing so, shake her hand. Then he had an
idea: he held out his hand to greet her, but this time he
had concealed a tack in his hand. She pulled her hand away.
The next time they met, although she still failed to recognise
him, she refused to shake his hand, but could not say why.
As LeDoux explains,
the learning of fear is based on a different system from
that of learning to identify people, objects and situations.
Fear learning is implicit. It depends on the amygdala. But
being able consciously to identify what causes the fear
depends on explicit learning, which needs intact hippocampal
regions and temporal lobes of the brain. Ordinarily if we
are frightened we feel the fear implicitly and know explicitly
what has caused it. Claparède's trick on his patient
showed that the avoidance response of fear can be learned
without consciousness--we can feel fearful but without knowing
why. This explains a lot. In many kinds of mental illness,
anticipatory fear (anxiety) has been conditioned to contexts,
some of which are not consciously known. Some of the most
common mental illnesses are caused by anxiety: generalised
anxiety states, panic disorders, social and other phobias,
obsessional-compulsive disorders. Other disorders, such
as depression and some psychoses, have anxiety as a component.
Although anxieties are easy to acquire, once their brain
circuits are established they are difficult or impossible
to delete. All therapies, whether they involve drugs, cognitive-behavioural
methods, or insight therapies such as psychoanalysis, therefore
have similar aims and perhaps similar effects. They act
not by undoing the anxiety, but by allowing patients to
live without being disabled by it.
But there may be
a problem in concentrating on fear and anxiety. These emotions
can easily be induced in reproducible experiments. What
about love? Neuroscientists have not yet discovered how
to evoke the powerful emotions involved in, for example,
falling in love (as opposed to the more predictable state
of ma-ternal bonding with offspring) and therefore cannot
investigate the mediatory role of the amygdala in this.
The Emotional
Brain is the second book on neural science of emotions
in recent years. The first was Descartes' Error: Emotion,
Reason and the Human Brain (Papermac, 1996) by Antonio
Damasio, with its idea of "somatic markers" of emotion (gut
feelings) and their relation to the frontal lobes. LeDoux
explains these somatic markers are usually conditioned fear
responses mediated by the amygdala. Damasio's book was good.
It rightly produced a stir. But LeDoux's book is better.
It is in tune with what psychologists know about emotions
and learning, is vivid and convincing in its description
of a central mechanism of emotion, and is directly applicable
to understanding anxiety, the most common ingredient of
emotional disorders. It's a terrifically good book.
Keith Oatley is professor of applied
psychology at the University of Toronto. His textbook Understanding
Emotions (Blackwell, 1995) was coauthored by Jennifer Jenkins.
