Ricerc@Sapienza

The recently renewed focus on the human exploration of outer space has boosted the
interest toward a variety of questions regarding health of astronauts and cosmonauts.
Among the others, sleep has traditionally been considered a central issue. To extend
the research chances, human sleep alterations have been investigated in several
analog environments, called ICEs (Isolated, Confined, and Extreme). ICEs share different
features with the spaceflight itself and have been implemented in natural facilities and
artificial simulations. The current paper presents a systematic review of research findings
on sleep disturbances in ICEs. We looked for evidence from studies run in polar
settings (mostly Antarctica) during space missions, Head-Down Bed-Rest protocols,
simulations, and in a few ICE-resembling settings such as caves and submarines.
Even though research has shown that sleep can be widely affected in ICEs, mostly
evidencing general and non-specific changes in REM and SWS sleep, results show a
very blurred picture, often with contradictory findings. The variable coexistence of the
many factors characterizing the ICE environments (such as isolation and confinement,
microgravity, circadian disentrainment, hypoxia, noise levels, and radiations) does not
provide a clear indication of what role is played by each factor per se or in association
one with each other in determining the pattern observed, and how. Most importantly,
a number of methodological limitations contribute immensely to the unclear pattern of
results reported in the literature. Among them, small sample sizes, small effect sizes, and
large variability among experimental conditions, protocols, and measurements make it
difficult to draw hints about whether sleep alterations in ICEs do exist due to the specific
environmental characteristics, and which of them plays a major role. More systematic
and cross-settings research is needed to address the mechanisms underlying the sleep
alterations in ICE environments and possibly develop appropriate countermeasures to
be used during long-term space missions.