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https://cc.arcabc.ca/islandora/object/cc%3Apsycjournal

J Camosun Psyc Res. (2023). Vol. 5(1), pp. 45-55.
Submitted Fall 2022; accepted June 2023.

What is The Biological Mechanism of Nightmares?
Authors: Lauren Radu* and Liz Snell
Supervising Instructor: Michael Pollock, Psyc 215 (“Biological Psychology”)
Department of Psychology, Camosun College, 3100 Foul Bay Road, Victoria, BC, Canada V8P 5J2
*Corresponding author email: laurenradu@hotmail.com

ABSTRACT
In this paper, we sought to understand what the biological mechanism of nightmares so that
we could learn how to overcome and improve our quality of sleep. Previous research has
predicted an increase in nightmares by variables such as sugar consumed prior to sleeping, an
increase in serotonin levels, and frontal alpha asymmetry. In our correlational study, we tested
the strength of these relationships by examining naturalistic daily changes in their variables
longitudinally over a period of one week. We measured food by grams of sugar consumed prior
to sleeping, serotonin levels by hours spent waking vs. sleeping, Frontal Alpha Asymmetry by
frontal alpha cortical waves during resting wakefulness using a Muse headband, and nightmares
by using the modified Differential Emotions Scale (see Appendix A). Data pooled across
participants did not find nightmares were significantly correlated with any of the three predictor
variables measured. These results suggest that those who seek to decrease nightmares should
attempt to do so via methods other than manipulating sugar intake or hours of sleep. The
biological cause of nightmares requires further research to be determined.
1. Introduction
1.1 Research Problem
Nightmares can alter the quality of sleep,
causing a lack of motivation and difficulty
focusing, and ultimately can directly affect
our health. After a nightmare, confusion,
anxiety, and even depression can appear the
next day. Also, sleep is one of the most
important elements that help people stay
alert during the daytime. Poor quality of
sleep due to a nightmare can lower one’s
performance in study and work. Fear
experienced during a nightmare may cross
over into waking life and increase anxiety
surrounding the specific frightening
elements of the nightmare. (E.g., a

nightmare about snakes may increase the
fear of real snakes.) Our goal of this research
was to understand the causes of nightmares
so that we can avoid having nightmares,
decrease anxiety, and improve quality of
sleep.
1.2 Literature Review
One factor previously found to predict an
increase in nightmares is the type of food
eaten prior to sleeping. For example, in a
correlational study by Nielsen & Powell
(2015), researchers surveyed 396 students to
find out which foods they noticed had the
greatest effect on the content of their dreams
over the past two weeks. Participants were
asked to complete a combination of seven
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questionnaires and scales. Their sleep
quality scale used a Likert Scale from one to
four ("rarely" to "almost always") and
included statements such as, “I wake up
easily due to noise,” and, “Poor sleep gives
me headaches.” Their three-factor eating
questionnaire included questions such as,
“When I feel really upset, I want to eat,”
and, “How often do you feel hungry?” An
intuitive eating scale included questions
such as, “I trust my body to tell me when to
stop eating,” and, “I use food to help me
soothe my negative emotions.” A diet
quality questionnaire included questions
such as, “Yesterday, did you eat any of the
following sweets: cakes, cookies,
biscuits…?” and, “Yesterday, did you eat
any of the following vegetables: carrots,
pumpkin, or sweet potatoes that are orange
inside…?” An eating behavior questionnaire
used a Likert Scale from one to five
("strongly disagree" to "strongly agree") and
included statements such as, “If I miss a
meal I get irritable,” and, “I enjoy tasting
new foods.” A perceived food-dependent
dreaming questionnaire used “...three binary
(yes/no) and three open-ended questions.
Two binary questions asked whether
participants had ever noticed foods that led
to disturbing dreams or bizarre dreams while
a third asked whether they had noticed if
eating late at night had affected their sleep
or dreams (Nielsen & Powell, 2015). Lastly,
researchers used a dream characteristics
questionnaire that consisted of seven items
assessing four aspects of disturbing dreams:
“recall frequency, clarity, realism, and
color” (Nielsen & Powell, 2015).
Participants noted dairy products were the
most likely to create bizarre dreams,
followed by sugary foods and spicy foods.
Based on these results, the researchers
suggested four possible causes of the
correlations noted: food-specific effects
(specific foods actually do affect dream

content), food-induced distress (specific
foods cause irritation to certain individuals,
affecting dream content and or/sleep
processes), folklore influences (belief that
certain foods will affect dream content
causes people to notice confirming examples
or to be more likely to have bizarre dreams),
and causal misattributions (a lack of internal
awareness leads people to look for external
causes for their dreams).
Another factor previously found to
predict intensity of nightmares is serotonin.
For example, in an experimental study by
Pace-Schott et al. (2001), researchers
measured the effects of two antidepressant
Selective Serotonin Reuptake Inhibitors
(SSRIs), paroxetine and fluvoxamine, on
psychologically normal participants. In a
double-blind experiment, participants were
first measured for seven days at baseline,
then were randomly assigned treatment with
either paroxetine or fluvoxamine for 19
days. After the treatment they were
measured for five days of acute
discontinuation of the drugs. Participants’
sleep was measured with the Nightcap
ambulatory sleep monitor, which they wore
every night during the baseline seven days,
the initial phase of treatment, and acute
discontinuation. From the sleep monitor,
researchers recorded REM eyelid movement
density and REM latency. Each morning
participants recorded the dreams they
recalled and scored each line of these reports
for its emotional content on a five-point
scale using six emotions (fear/anxiety,
anger, sadness, shame, joy/elation, and
affection/erotic). Participants then
completed a questionnaire regarding sleep
quality and dream features, which featured
seven questions on a five-point Likert scale
rating dreams for memorability, visual
vividness, amount of sound, amount of
movement, emotional intensity,
meaningfulness, and strangeness. The
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subjective dream reports were typed up by
an assistant and scored for content
(bizarreness, fictive movement, and visual
nouns) by three judges who were blind to
participant identity.
Researchers found that while dream
recall and REM sleep both decreased during
SSRI treatment, intensity of dreams
increased both during steady state drug
treatment and acute discontinuation. Dreams
were most bizarre during acute
discontinuation for participants who had
received fluvoxamine. Based on these
results, researchers concluded that the
increased brain arousal associated with
aminergic SSRIs may contribute to dream
intensity participants experienced while
under SSRI treatment.
A third factor previously found to
predict an increase in nightmares is Frontal
Alpha Asymmetry (FAA). For example, in
an experimental study by Sikka et al. (2019),
over two nights in the lab researchers
awakened participants every five minutes
during REM sleep and had them orally
report their dream content. Participants then
rated their dream affect using a Likert scale,
the modified Differential Emotions Scale
(mDES), which included questions such as,
“What is the most stressed, nervous, or
overwhelmed you felt?” and, “What is the
most joyful, glad, or happy you felt?” Two
external judges read the dream reports and
rated the affect expressed in the reports
using the same Likert scale. Participants also
rated their affect before going to sleep.
Researchers used EEG to measure
participants’ brain activity during resting
wakefulness and REM sleep. They recorded
Frontal Alpha Asymmetry; that is, the
difference in alpha power between right and
left frontal cortical regions. Based on
previous studies, decreased alpha power in
the left frontal area/increased alpha power in
the right frontal area has been found to

predict both trait and state anger. In the
Sikka et al. study, both the EEG
measurements and the dream reports showed
that increased alpha power in the right
frontal region while sleeping also predicted
anger experienced in dreams. They also
found that FAA experienced in a resting
wakeful state predicted dream anger. The
only other dream affect predicted by FAA
was Hate/Distrust/Suspicion, which
researchers considered to be highly related
to anger. Based on these results, the
researchers suggested that dreaming and
waking anger are similar in how they are
expressed through brain activity, and that
people who experience more alpha power in
the right frontal cortex while waking are
more likely to experience anger in
subsequent dreams.
1.3 Hypotheses
Based on the above literature review, we
predicted the following hypotheses:
· Hypothesis #1: If sugar intake increases
then nightmares will tend to increase.
· Hypothesis #2: If serotonin level
increases then nightmares will tend to
increase.
· Hypothesis #3: If right frontal cortical
region alpha waves increase during sleep
then nightmares will tend to increase.
2. Methods
2.1 Participants
The three authors of this paper served as
the participants in its studies. The
participants ranged in age from 22 to 36
years old, with an average age of 27 years,
and included two females. The participants
were all undergraduate students at Camosun
College who completed the current studies
as an assignment for Psyc 215
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(“Biopsychology”) and were grouped
together due to their mutual interest in
nightmares.
2.2 Materials and Procedures
We first performed a correlational study
to concurrently test all our hypotheses by
examining naturalistic daily changes in their
variables longitudinally. Each participant
kept a study journal with them at all times
over this study’s one-week period in order to
record self-observations of the following
three variables: (1) sugar consumed, (2)
serotonin levels, (3) right frontal cortical
region alpha waves.
Food Consumption - To measure how the
type of food consumed prior to sleeping
affects dreams, for 11 days participants used
a journal to record the food they consumed
prior to sleeping and the dreams they could
recall the next morning. Prior to sleeping
they recorded the grams of sugar in the last
food they consumed before sleeping. The
next morning, within 10 minutes of waking,
they recorded in their journal what they
could recall from their dreams that night and
rated their dream affect using the modified
Differential Emotions Scale (see Appendix
A for a complete list of items used in this
questionnaire).
Serotonin - To measure how serotonin
levels affect the presence of nightmares, for
11 days participants used a journal to record
the number of hours they were awake during
the day. This was because serotonin levels
increase during waking. On the other hand,
serotonin levels decrease during sleep, so
participants were also asked to record the
number of hours they were asleep during the
night.
Frontal Alpha Asymmetry - To measure
FAA, we used an EEG device, the Muse
headband. Participants wore the headband
during resting wakefulness for two minutes
in each recording, measured for 11 days.

Both left and right frontal alpha waves were
recorded. FAA measurements were
compared with participants’ reported dream
affect to see whether resting wakefulness
activity in the frontal cortex had a
relationship to participants’ dream affect.
Nightmares - To measure nightmares, we
used the Modified Differential Emotions
Scale (see Appendix A). Participants
recorded any dreams they remembered in a
journal each morning and then rated their
dream affect using the Modified Differential
Emotions Scale. We calculated our score by
adding together the score of all questions
recorded by each participant.
2.3 Statistical Analyses
To assess the strength and statistical
significance of associations between
variables predicted by our three hypotheses,
we performed Pearson product-moment
correlations of their predictor variables sugar
intake, serotonin levels, and right frontal
cortical alpha waves with their outcome
variable (increase in nightmares). For testing
Hypothesis #1, we correlated sugar intake
with an increase in nightmares. For testing
Hypothesis #2, we correlated serotonin
levels with an increase in nightmares. For
testing Hypothesis #3, we correlated right
frontal cortical alpha waves with an increase
in nightmares. We performed all the above
correlations separately for each participant
as well as using data pooled across all the
participants. For the correlations using
pooled data, in addition to using the raw
data, we also performed correlations after
we had first transformed the data from each
participant into z-scores in order to
standardize differences in averages and
variability seen between the participants in
their data and thus make them more
comparable. A correlation coefficient was
considered statistically significant if the
probability of its random occurrence (p) was
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< .05 (i.e., less than 5% of the time expected
by chance alone).

alpha waves did not affect participants’ level
of nightmares.

3. Results

4.2 Relation of Results to Past Research

This study did not find statistical
significance for the correlation of
nightmares with any of the three variables
measured (see Table 1). Sugary foods did
not exhibit any correlation to nightmares,
either in pooled raw data (r = -0.05, p =
0.83; see Figure 1) or pooled standardized
data (r = 0.32, p = 0.15; see Figure 2). The
association between serotonin and
nightmares was not significant for either
pooled raw data (r = -0.16, p = 0.48; see
Figure 3) or pooled standardized data (r =
0.24, p = 0.29; see Figure 4). Right frontal
alpha did not correlate significantly with
nightmares in pooled raw data (r = 0.09, p =
0.72; see Figure 5) or pooled standardized
data (r = 0.10, p = 0.69; see Figure 6).
Although it did not reach statistical
significance, sugar showed the strongest
correlation, with the pooled standardized
data at p = 0.32.

Our correlational study failed to confirm
the relationship between the amount of sugar
consumed prior to sleeping and an increase
in nightmares reported by previous research.
Nielsen and Powell (2015) found that an
increase in the amount of sugar consumed
prior to sleeping increased the chances of
having a nightmare. One way our
correlational study differed from that of
Nielsen and Powell (2015) is that we did not
record the kind of sugar being consumed:
processed, refined, or natural. In previous
research, refined sugar was found to have
the highest correlation with an increase in
nightmares. We recommend that future
studies record not only the amount of sugar
consumed but the type of sugar being
consumed, which can allow researchers to
measure results more precisely.
Our correlational study failed to confirm
the relationship between serotonin levels
during waking and an increase in nightmares
reported by previous research. An increase
in serotonin had previously been found to
correlate with an increase in nightmares
(Pace-Schott et al., 2001). Participants in the
original study were given SSRIs to increase
serotonin, whereas we measured serotonin
increase due to wakefulness versus sleeping.
Our serotonin manipulation may not have
been strong enough to create significant
results.
Our correlational study failed to confirm
the relationship between right frontal
cortical alpha waves and an increase in
nightmares reported by previous research
(Sikka et al., 2019). Unlike the original
study, we did not take EEG measurements
close to sleeping, which may have resulted
in less overlap between resting wakefulness

4. Discussion
4.1 Summary of Results
Based on previous research, we
hypothesized that increases in three
variables would be followed by an increase
in nightmares: the amount of sugar
consumed prior to sleeping (Hypothesis #1),
an increase in serotonin levels during
waking (Hypothesis #2), and an increase in
right frontal cortical alpha waves
(Hypothesis #3). Data pooled across
participants in our correlational study did
not support the predicted relationships. The
result suggests that increased levels of sugar,
serotonin, and right frontal cortical region

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and dream states. We also did not measure
EEG while participants were asleep, relying
instead only on the mDES for our definition
of nightmares. Therefore, we could not see
the correlation between waking and sleeping
right frontal cortical alpha waves, which
may have given us more significant results.

hours awake as a means to decrease
nightmares. Further research is needed to
gain more understanding of the
biopsychological factors of nightmares. This
may eventually lead to solutions that will
decrease the anxiety and impact on sleep
caused by nightmares.

4.3 Implications of Results

References

Our study did not find statistical
significance for any of the three variables
measured: sugar consumed prior to sleeping,
serotonin levels during waking, and right
frontal cortical alpha waves. Data was
collected throughout an 11-day period. Even
though this amount of time gave our
correlational study statistical power, the lack
of statistical significance may have been due
in part to our small sample size.
We originally wanted to understand the
biopsychological causes of nightmares to
prevent their frequency. Our correlational
study did not find statistical significance.
From our research, it appears that neither
amount of sugar consumed prior to sleeping,
hours spent awake, nor resting wakeful right
frontal alpha waves predict the emotional
content of dreams we experience. The
results of our correlational study suggest that
people experiencing nightmares should not
attempt to alter sugar intake or amount of

Nielsen, T., & Powell, R. A. (2015). Dreams
of the rarebit fiend: Food and diet as
instigators of bizarre and disturbing
dreams. Frontiers in Psychology, 6.
https://doi.org/10.3389/fpsyg.2015.00047
Pace-Schott, E, F., Gersh, T., Silvestri, R.,
Stickgold, R., Salzman, C., & Hobson, J.
A. (2001). SSRIs Treatment suppresses
dream recall frequency but increases
subjective dream intensity in normal
subjects. Journal of Sleep Research,
10(2), 129-142.
https://doi.org/10.1046/j.13652869.2001.00249.x
Sikka, P., Revonsuo, A., Noreika, V., Valli,
K. (2019). EEG frontal alpha asymmetry
and dream affect: Alpha oscillations over
the right frontal cortex during REM sleep
and presleep wakefulness predict anger in
REM sleep dreams. The Journal of
Neuroscience, 39(24), 4775-4784.
doi:10.1523/JNEUROSCI.2884-18.2019

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Table 1
Correlations for Study Variables

Variables

Sugar and

Participant #1 Participant #2

Pooled raw
data

Pooled
standardized
data

r

n

r

n

r

n

r

n

0.21

11

0.44

11

-0.05

22

0.32

22

0.07

11

0.41

11

-0.16

22

0.24

22

0.42

10

-0.23

10

0.09

20

0.10

20

nightmares

Serotonin and
nightmares

Right Frontal
Alpha and
nightmares

Notes. r = correlation coefficient, n = number of days sampled.
* p < .05.

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Figure 1
Association Between Sugar and Nightmares Using Pooled Raw Data

Notes. Marker colour differentiates participants: red = participant #1 and orange = participant #2.
Some data might not be visible in the figure due to overlapping markers.

Figure 2
Association Between Serotonin and Nightmares Using Pooled Standardized Data

Notes. Marker colour differentiates participants: red = participant #1 and orange = participant #2.
Some data might not be visible in the figure due to overlapping markers.
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Figure 3
Association Between Right Frontal Alpha and Nightmares Using Pooled Raw Data

Notes. Marker colour differentiates participants: red = participant #1 and orange = participant #2.
Some data might not be visible in the figure due to overlapping markers.

Figure 4
Association Between Sugar and Nightmares Using Pooled Standardized Data

Notes. Marker colour differentiates participants: red = participant #1 and orange = participant #2.
Some data might not be visible in the figure due to overlapping markers.
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Figure 5
Association Between Serotonin and Nightmares Using Pooled Standardized Data

Notes. Marker colour differentiates participants: red = participant #1 and orange = participant #2.
Some data might not be visible in the figure due to overlapping markers.

Figure 6
Association Between Right Frontal Alpha and Nightmares Using Pooled Standardized Data

Notes. Marker colour differentiates participants: red = participant #1 and orange = participant #2.
Some data might not be visible in the figure due to overlapping markers.
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Appendix A
Modified Differential Emotions Scale (mDES)
Instructions:
Please think back to how you have felt during the past 24 hours. Using the 0-4 scale below, indicate the
greatest amount that you’ve experienced each of the following feelings.
0 = Not at all, 1 = A little bit, 2 = moderately, 3 = Quite a bit, and 4 = Extremely
___1. What is the most amused, fun-loving, or silly you felt?
___ 2. What is the most angry, irritated, or annoyed you felt?
___3. What is the most ashamed, humiliated, or disgraced you felt?
___4. What is the most awe, wonder, or amazement you felt?
___5. What is the most contemptuous, scornful, or disdainful you felt?
___6. What is the most disgust, distaste, or revulsion you felt?
___7. What is the most embarrassed, self-conscious, or blushing you felt?
___8. What is the most grateful, appreciative, or thankful you felt?
___9. What is the most guilty, repentant, or blameworthy you felt?
___ 10. What is the most hate, distrust, or suspicion you felt?
___11. What is the most hopeful, optimistic, or encouraged you felt?
___12. What is the most inspired, uplifted, or elevated you felt?
___13. What is the most interested, alert, or curious you felt?
___14. What is the most joyful, glad, or happy you felt?
___15. What is the most love, closeness, or trust you felt?
___16. What is the most proud, confident, or self-assured you felt?
___17. What is the most sad, downhearted, or unhappy you felt?
___ 18. What is the most scared, fearful, or afraid you felt?
___19. What is the most serene, content, or peaceful you felt?
___20. What is the most stressed, nervous, or overwhelmed you felt?
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