The
Scent of Fear
Kerstin
Ackerl,
Michaela Atzmueller,
Karl Grammer
Ludwig-Boltzmann-Institute
for Urban Ethology at the Institute of Anthropology/University
of Vienna.
Submitted:
April 2, 2002
Accepted: April 3, 2002
Key words:
fear, human pheromones, cortisol,
olfactory communication, alarm substances
Abstract
In
this study we tried to find out if fear can be detected from
human body odours. Female subjects wore under-arm axillary pads
while watching a terryfying film. Saliva cortisol samples were
taken before and after the film presentation as a hormonal measure
for the fear response. The fear experience itself was measured
by Spielberger’s State-Trait Anxiety Inventory. A “neutral”
film, shown one day after the “fear” film, was used as a control
in a repeated measures design. In part two of the experiment,
the axillary pads were presented to female subjects in a triple
forced choice test. Results show that subjects were able to
discriminate between fear and non-fear axillary pads, suggesting
that women are indeed able to detect “the scent of fear”. A
direct correlation between induced fear, changes in cortisol
levels and smell ratings could not be established. Thus cortisol
levels are probably not the inducer of the scent of fear and
a hypothetical fear pheromone could have other origins.
...
...
People
have always used scents to either mask their body odour or to
express and emphasize their moods or appearance. The possibility
that odours can also provide relevant biological information
about their “sender” has only in recent years become
the focus of scientific attention. Doty [1] described the advantages
of olfactory communication as follows: the sense of smell even
works if the other two “major” senses (visual and
acoustic) are functionally restricted (for example if it is
too dark or too loud). Moreover, odourous substances can easily
be spread over large areas and can last for a long time. Intensity,
distribution, and quality of scent marks can give information
about size, reproductional and nutritional status, etc. of an
individual without immediately drawing unwanted attention to
the sender (e.g. detection from a predator via the loud noise,
etc. of a sender). Another advantage in communication through
odours lies in the fact that sender and receiver
don’t have to be in close spatial distance in order to
communicate.
The
question then becomes prominent: if olfactory communication
is useful in other animals, why is it not used by human as well?
In recent years this assumption has undergone major revision.
Several studies indicate that humans do indeed seem to use olfactory
communication and are even able to produce and perceive certain
pheromones (for a detailed overview see [2]). Up to now most
studies were looking at human pheromones linked to the sex hormones,
the question of whether humans are or are not able to communicate
other than sex-related information through odours has yet to
be raised.
Fear arises in stressful situations that are subjectively perceived
as threatening. The intensity of the induced negative feeling
corresponds to the subjective perception of threat in a situation.
If the negative feeling becomes too intense, a seeking-reaction
for stress-relieving mechanisms is initiated [3].
Fear can be induced by external, objective threats (e. g. predators),
as well as by internal, subjective threats, called “free
floating anxieties”[4]. Free floating anxieties can be
generated by conscious or subconscious memories of threatening
experiences in the past, or by the mere anticipation of a stressful
situation.
The assumption that fear is a learned avoidance reaction to
potentially dangerous situations is gradually being questioned.
Recent studies show that fear may be a genetically determined
function of the nervous system [4]. This hypothesis receives
support from an evolutionary point of view. The ability to detect
and anticipate dangerous situations seems to be crucial for
survival, and individual learning might not be entirely quick
enough to ensure survival chances. Moreover, even potentially
dangerous stimuli might be rare and thus impossible to learn
– leading an individual into danger when the stimulus is
encountered for the first time.
Panksepp [4] describes a “major fear circuit” in the
brain located within the lateral and central parts of the amygdala
in the lobus temporalis, the periaquaeductal grey (PAG) of the
diencephalon and mesencephalon, and as “output-generating”
parts the brain stem and the medulla.
Fear leads to reactions that are both behavioral and physiological.
Behavioral reactions include either a “freeze”, “flight”,
or “fight” response. Underlying physiological processes
include an increase in heart rate, muscular tension, sweating,
etc., and, most important, a response of the adrenal gland via
the pituitary-hypothalamus-adrenal-axis (HHN) which leads to
the release of cortisol. The cortisol level rises as a consequence
of the production of corticotropin releasing hormone and ACTH
[5]. Thus in many experiments the assessment of changes in cortisol
levels is used as an indicator of potentially experienced fear.
In a study by Hubert & de Jong-Meyer [6] male subjects showed
an increase in cortisol levels (measured from saliva) while
they were watching a horror film. Kirschbaum & Hellhammer
[7] found similar results. In contrast, Hubert, Möller,
& de Jong-Meyer [8] showed that subjects experienced an
increase in cortisol levels in response to a funny movie. The
authors speculate that every kind of affective arousal and change
of mood, positive as well as negative, could be linked to cortisol
secretion.
Besides fear inducing situations, everyday stressors, the so-called
“daily hassles”, can also provoke a raise in cortisol
levels [9; 10]. In fact, it seems that the mere anticipation
of a stressful experience can have this effect [11].
It thus remains doubtful that cortisol secretions might function
solely as a result of experiencing fear. Cortisol raises in
such situations could also be due to the stressing effects of
fear.
Alarm pheromones were found in fish as early as 1941 by Von
Frisch [12] and have since then been found in many species.
Today we know that at least insects, annelids, and fish use
olfactory signals to inform their conspecifics about stress,
alarm, and fear. In ants, for example, alarm substances can
cause aggregation, dispersion, or defense of the colony depending
on the sender’s status [13]. The use of alarm pheromones
has also been demonstrated in bees (Apis mellifera) [14] and
lice (Acyrthosiphon pisum) [15]. On “defective stimulation”
earthworms (Lumbricus terrestris) give off a substance that
makes their conspecifics avoid their area and thus potential
predators [16]. Among vertebrates, fish are the best known example
for the use of alarm substances: fathead minnows (Pimephales
promelas) that have never before been confronted with a pike
(Esox lucius) immediately “know” that it is a dangerous
predator because the pike seems to get marked by an “odour
label” by every minnow it actually catches [17]. Sources
of alarm substances in minnows are for example urine, feces,
and mucus.
Mammals also seem to use olfactory alarm signals. Valenta &
Rigby [18] were able to show that rats can distinguish between
the odour of stressed and “relaxed” conspecifics.
Carr, Martorano & Krames [19] found that male mice prefer
the smell of conspecifics that have just won a fight over the
smell conspecifics that have not won a fight, and the smell
of conspecifics that haven’t been experimentally shocked,
over the smell of conspecifics that have been treated with electric
shocks.
In predator-prey-interactions between Mongolian jirds (Meriones
unguiculatus) and cats it was shown that the stressed mice mark
the “dangerous areas” with their scent and thus tell
their conspecifics to avoid these areas, while cats orientated
themselves by the scent of stressed mice in order to find them
[20].
If other mammals are able to warn their conspecifics –
or at least send out the information that they are in a frightening
situation – by emitting odourous substances, the question
becomes prominent: Do humans possess similar mechanisms? If
so, how are these mechanisms related to cortisol release? The
current research aims to address these questions.
Methods
... ...
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