The aim of this study was to investigate hyperarousal in individuals with frequent
nightmares (NM participants) by calculating arousal events during nocturnal sleep.
We hypothesized an increased number of arousals in NM participants compared with controls,
especially during those periods where the probability of spontaneous arousal occurrence
is already high, such as non-rapid eye movement to rapid eye movement transitions
(pre-rapid eye movement periods). Twenty-two NM participants and 23 control participants
spent two consecutive nights in our sleep laboratory, monitored by polysomnography.
Arousal number and arousal length were calculated only for the second night, for 10
min before rapid eye movement (pre-rapid eye movement) and 10 min after rapid eye
movement (post-rapid eye movement) periods, as well as non-rapid eye movement and
rapid eye movement phases separately. Repeated-measures ANOVA model testing revealed
significant Group (NM participants, controls) x Phase (pre-rapid eye movement, post-rapid
eye movement) interaction in case of the number of arousals. Furthermore, post hoc
analysis showed a significantly increased number of arousals during pre-rapid eye
movement periods in NM participants, compared with controls, a difference that disappeared
in post-rapid eye movement periods. We propose that focusing the analyses of arousals
specifically on state transitory periods offers a unique perspective into the fragile
balance between the sleep-promoting and arousal systems. This outlook revealed an
increased number of arousals in NM participants, reflecting hyperarousal during pre-rapid
eye movement periods.
