The first-night effect in sleep polysomnographic studies is usually conside
red to last for one night. However, a few observations have indicated that
variables associated to rapid eye movement sleep take longer to stabilize.
Notwithstanding, current opinion holds that second nights of recording can
be used without restriction for research and clinical purposes. The goal of
this study was to describe the dynamics of habituation to polysomnography
in optimal conditions. Twenty-six young, carefully screened, healthy subjec
ts were recorded in their home for four consecutive full polysomnographies.
Repeated measures ANOVA were applied. Between the two first nights, while
there were no differences in sleep duration in non-rapid eye movement sleep
, marked modifications in corresponding spectral power were observed. The d
ynamics of adaptation of rapid eye movement sleep appeared to be a process
extending up to the fourth night. Similar dynamics in NREMS and REMS homeos
tasis have been observed in sleep deprivation studies, and it appears that
the same mechanisms may be responsible for the FNE. The longer habituation
process of REMS in particular has important implications for sleep research
in psychiatry. (C) 2001 Elsevier Science Ltd. All rights reserved.