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
Introduction - Various researchers
have hypothesized that the differences in cognition between REM
and NREM sleep may be assessed by testing performance on cognitive
tasks immediately upon awakening, or soon after waking. The
theoretical basis for this method is that the neurochemistry of
REM and NREM sleep persists briefly after waking. The basis for
the choice of some of the cognitive tasks has been that REM dreams
are more frequent, vivid and bizarre than are NREM dreams, and so
various creativity-style tasks have been used. Matthew Walker et
al (2002) showed significantly better solving of anagrams within
90 seconds of being awoken from REM sleep than from NREM sleep.
This indicates that REM sleep can support cognitive flexibility to
a greater extent than can NREM sleep, and it may be that this
difference between the sleep states results in REM dreams being
more bizarre and vivid than NREM dreams.
Walker et al had participants answer
8 anagrams before sleep, 8 upon being woken from REM sleep, 8 upon
being woken from NREM sleep, and 8 in the morning. The four sets
of anagrams had been designed to be of equal difficulty. They
found that significantly more anagrams were answered correctly
after REM awakenings than after NREM awakenings.
Method - We aimed to repeat the
study of Walker et al (2002), but with a time delay so that the
anagrams were answered 4 minutes after awakening. 16 participants
slept in the sleep laboratory at Swansea University and were
awoken 10 minutes from the start of a REM period and 10 minutes
from the start of a NREM period, the order of REM/NREM awakenings
was counterbalanced across participants.
Results - Number of correctly
answered anagrams were: evening before sleep, mean = 3.31 (SD =
1.78). REM awakening, mean = 2.63 (1.96); NREM awakening, 2.63
(1.36), morning after breakfast, mean = 2.69 (1.40).
Discussion - We conclude that the
neurochemical differences between REM and NREM sleep 90 seconds
after awakening that resulted in the results of Walker et al
(2002) have diminished or disappeared within four minutes of
awakening. We discuss the implications of these results, and this
methodology, for the investigation of how dreams are created in
REM sleep, and for how REM dreams differ from NREM dreams.
Reference
Walker, MP, Liston, C, Hobson, JA, &
Stickgold, R. (2002). Cognitive flexibility across the sleep-wake
cycle: REM-sleep enhancement of anagram problem solving. Cognitive
Brain Research, 14, 317-324.
