The Effect of Stimulating and Soothing
Smells on Heart Rate and Memory
by Rachanee N. Jackson
Faculty Mentor: Dr. Kimberly Roberts
abstract
This study was performed to investigate the effect of smell on heart rate and short-term
memory. Lemon and lavender were used as stimulating and soothing scents respectively,
in order to determine if these odors increased or decreased heart rate and correspondingly
improved or impaired memory. Sixty-seven participants from California State University,
Sacramento were divided into three groups to test the hypothesis that the stimulating scent
of lemon would enhance memory and increase heart rate, whereas lavender would reduce
memory and decrease heart rate. However, the results from this study were not statistically
significant to support this claim.
Our olfactory sense is unlike any other sensory modality. It is the
only sense that is directly connected to the environment, has neurons that
continuously regenerate throughout life, and has neuron axons that are
unmyelinated. Having “unmyelinated axons” means that neurons’ axons are
not surrounded by protective cells called “glial cells.” Glial cells make up
myelin, which is a protective layer of cells around the cell axon that allows
for fast transmission of information from one neuron to the next. Not being
myelinated causes the sensory signal from the environment to the olfactory
bulbs (the structure that perceives smells) to move slower, which is why there
is a delay in our responses to smell, and why smells linger in our noses after
the scent in the air has passed.
The olfactory system contains structures that are also components of the
limbic system, the center that is in charge of emotion and sensory processing.
Among these structures is the amygdala, which is involved with emotional
processing, specifically fear; and the hypothalamus, which maintains
homeostasis within the body; and the hippocampus, which is involved in
forming new long-term memories. The olfactory system’s close location to
the limbic system explains why certain smells bring back such strong, vivid,
emotional memories. The first time we come in contact with a special smell
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like the smell of one’s grandparent or the smell of art paste, it gets stored
in our memories so the next time we smell that scent we are taken back to
a loved one’s hugs or to preschool art class. The proximity of these two
systems would also explain why certain odors can cause relaxation, increased
or decreased heart rate, and many other physiological responses in the body.
Scholars have studied how heart rate affects cognition and memory (Jennings
and Hall 1980; Luft et al. 2009; Hansen et al. 2007) and how olfaction can
alter physiological responses (Xu et al. 2008; Duan et al. 2007; Herz 2009),
but no research exists on the relationship between heart rate and memory as
the result of a stimulating odor.
The most relevant literature to the present research is in aromatherapy studies.
Aromatherapy is a therapeutic method in which aromatic essential oils are
extracted from plants and commonly inhaled to enhance different responses.
There exists no concrete evidence that either confirms or denies the therapeutic
benefits of aromatherapy so there are skeptics to the idea. However, there is
extensive research (Xu et al. 2008; Duan et al. 2007; Herz 2009) suggesting
that certain essential oils can and do create physiological, emotional, and
psychological responses. Sandalwood for example, produces a sedating, relaxing
feeling, which tends to be useful for treating people with anxiety, depression
and insomnia, while lavender is an uplifting scent that is soothing and helpful
in minimizing stress, anxiety, negative emotions, and insomnia (Herz 2009).
Rosemary has been known to clear the mind and stimulate memory, while clary
sage is an uplifting odor that relaxes patients and helps with anxiety, depression,
fatigue, and irritability (Herz 2009). Lemon has been found to improve memory
but it does not have any other physical effects on patients (Harvard Women’s
Health Watch 2008). There have been studies that have investigated the effect
of aromatherapy on depression (Yim et al. 2009; van der Watt and Laugharne
2008), irritability, dementia (Ballard 2007), and emotional diseases (Butje,
Repede, and Shattell 2008), but no research connects stimulating scents with a
direct influence on memory.
Although there have been studies on the effects of different odors on heart
rate and on the effects of heart rate on memory and cognition, no research
has been conducted on whether odors that increase heart rate also increase
memory. The present study will use subjects from California State University,
Sacramento to examine whether the stimulating smell of lemon and the
relaxing smell of lavender, when presented to subjects, will cause their heart
rates to increase or decrease and if there is a relationship between how well
participants are able to recall information.
McNair Scholars Journal ▪ Volume 11
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literature review
“Aromatherapy” is the use of essential oils that are extracted from plants
through distillation in order to treat physical and psychological health issues.
It is a branch of “phytotherapy,” which is the use of part of or an entire
plant for medical purposes (Stelflitsch and Stelflitsch 2008). Essential oils
have been utilized for therapeutic and medicinal purposes for centuries.
Today, these oils are commonly used in massage oils, in baths, and are
inhaled through steam or a diffuser to calm people, relieve irritability, aid
in treating insomnia, and help with pain. There are many other uses for
aromatherapy that are not as common, but when used by a specialist, a
person who has been certified in the use of aromatherapy, it can be used to
help treat inflammation, deodorize, increase blood flow to certain tissues in
the body, or for many other beneficial purposes (Stelflitsch and Stelflitsch
2008). There are hundreds of essential oils that provoke different responses
in people. Some of the odorants that have been prescribed to cause certain
healing reactions include: sweet marjoram (to calm, sedate, and relieve an
assortment of negative emotions like irritability, loneliness, and anxiety);
sandalwood (also used to sedate, relax, and aid in treating depression, anxiety,
and insomnia); and clary sage (to uplift, help relieve anxiety and depression,
aid in fatigue, and calm irritable children). Two of the most popular scents
studied in aromatherapy are rosemary, which stimulates memory and clears
the mind, and lavender, which is uplifting, calming, and useful for reducing
stress, anxiety, depression, and insomnia (Price 1991; as cited in Herz 2009).
There is not enough evidence to scientifically prove the medical benefits
of essential oils, but many studies have shown the effects that essential oils
can have on people (Glaser and Graham 2008; Duan et al. 2007; Moss et al.
2003). Despite the studies done, the skeptics remain.
Some disbelievers of aromatherapy give the argument that the expectancy
effect is the reason for the changes that researchers find in participants
(Howard and Hughes 2008). In their study, Howard and Hughes (2008)
suggest that studies that examined the consequence of lavender on
participants are flawed. They suggest that researchers tell participants what
changes the aromas should cause, or subjects are primed in some way to
the purpose of the study. The researchers further argued that these actions
influence such expected responses by the subjects. When people are aware
that a certain smell is supposed to induce or reduce relaxation, they will
become more or less relaxed depending on the expectation, and they will
report as such. Howard and Hughes (2008) also suggest that many studies
do not provide a placebo or blind experimental protocols to determine if a
placebo effect exists or if experimenter expectancy causes the anticipated
change. These researchers utilized a placebo in their study and manipulated
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the expectations of the subjects (2008). They found that the participants
who were primed to believe that the odor would make them more relaxed
were more relaxed, and those who were told that the oil’s scent would inhibit
them from relaxing were least relaxed of all the conditions. The groups that
were not primed measured in the middle of the two manipulated groups
despite whether they were in the lavender or placebo conditions (Howard
and Hughes 2008). Although expectations can produce fallacies in research,
the Howard and Hughes’ study is not comprehensive enough to disprove all
lavender studies. In order to have a well-constructed experiment with valid
data, one must control for such error as expectations. Controlling for fallacies
is the foundation of valid research and many researchers control for these
errors (Moss et al. 2002; Xu et al. 2008; Glaser et al. 2007). In addition, the
olfactory system in humans is very complex.
Olfactory System
The olfactory system is the only sensory system that reaches directly to the
cerebral cortex without first going through the thalamus (a structure that
sends signals to different sensory locations and manages consciousness
and alertness). When smells enter the nose, they activate olfactory receptor
cells called cilia that take the signal from the nose to the olfactory bulb
where the odor gets perceived. In the olfactory bulb, mitral cells pick up
the odor signal and transport it down the olfactory tract where the signal
is distributed to different parts of the limbic system (Chulder 2010). The
limbic system is most commonly known for maintaining balance within the
body through the use of hormones and the processing of emotions, but is
also used in handling higher order sensory processes and in the formation
of memories (Boeree 2009; Hesselink n.d.; Barker et al. 2003, 103-4). There
are primary and secondary olfact