Mark Blagrove, PhD, is Reader
in Psychology at the University of Wales Swansea, where he runs a
sleep laboratory and conducts research into the psychology of
dreaming. He is a Past President of IASD, and is a consulting
editor for the journal Dreaming and the Journal of Sleep Research.
Abstract
Many studies find only a small
relationship between proposed causes of nightmares and nightmare
frequency. For example, table 1 in Blagrove and Hayward (2006)
shows that most studies of the relationship between anxiety and
nightmare frequency find only low correlations. Furthermore,
Cellucci and Lawrence (1978) found only a few subjects to have
significant associations between their anxiety across the days of
the study and the occurrence of nightmares on each night. We
therefore raise the question, are some people more susceptible to
certain causes of nightmares than are others? Schredl (2003)
proposed such an interaction between trait and state factors, but
found that although neuroticism and boundary thinness were related
to nightmare frequency, these trait measures did not add to the
variance explained by the state measures.
This paper proposes that a relevant
trait is the number of nightmares that people have before the
state factor occurs. Thus, it is only people who already have
nightmares who show an increase in nightmare frequency due to such
state factors.
This is illustrated with a review of
the literature of the effects of the anaesthetic drug ketamine on
dreaming. Some studies have found ketamine causes more pleasant
dreams, but many studies have found it causes nightmares. This
lack of consistent findings is shown to be a result of studies not
taking account of the baseline number of nightmares that people
have at home before being given ketamine. It is suggested that
future studies on causes of nightmares partial out the trait of
baseline nightmare frequency.
References
Blagrove, M & Hayward, S. (2006).
Evaluating the awakening criterion in the definition of
nightmares: how certain are people that a nightmare woke them up?
Journal of Sleep Research, 2006.
Cellucci, A. J., and P. S. Lawrence.
(1978). Individual differences in self-reported sleep variable
correlations among nightmare sufferers. Journal of Clinical
Psychology 34(3):721-25.
Schredl, M.(2003). Effects of state
and trait factors on nightmare frequency. Eur Arch Psychiatry Clin
Neurosci. 2003 Oct;253(5):241-7.
