Pilot study to determine clock-related nonvisual effects of light on alertness and metabolism

The forced desynchrony (FD) protocol is a common method in chronobiology to
disentangle homeostatic (e.g. sleep pressure buildup during waking and
dissipation during sleep) and circadian-clock (e.g. 24-hour rhythmicity in
sleepiness) related effects on rhythmic behavioral or physiological processes.
Such protocols typically involve the observation of participants in the
laboratory over multiple weeks under dim light (~5 lux) conditions. We want to
perform a pilot study to obtain an indication of whether the FD protocol can
also be performed under bright light conditions to test whether the effect of
light on output parameters (e.g. alertness, sleep, heart rate, metabolism and
core body temperature) is under circadian control. In addition, we are
interested to test whether an FD of 3 days can be used to disentangle
homeostatic and circadian components affecting the rhythmicity of these output
parameters. In the future, such short FD protocols will decrease the burden
experienced by participants when disentangling clock- and homeostatic related
factors impacting rhythmicity of physiological and behavioural processes.
Additionally, this pilot is crucial in knowing whether a short FD protocol
under bright light can be used to study clock-related effects of light on many
rhythmic processes.

To test whether a short FD protocol can be used to test whether effects of
light on alertness, sleep, metabolism and temperature are under circadian
control.

This study will involve one 3-day FD protocol preceded and followed by 1
clock-phase assessment (dim-light melatonin onset). Light intensity during
wakefulness in the FD will be 5 lux. Three weeks later the same procedure will
be repeated, with an FD where light intensity levels of 1500 lux during
wakefulness are used. A separate group of individuals will perform both
procedures in reversed order.

2 3-day FD protocols separated by a 3-week rehabilitation period

Subjects will remain for 4 days and 5 nights in the human isolation facility of
the University of Groningen. They will remain here under an alternative
day-night cycle (13 hours awake, 5 hours sleep). Multiple saliva samples will
be taken and in addition, subjects will fill in questionnaires and perform
reaction time tasks. Body temperature, heart rate, metabolism and brain
activity will also be measured.
Preceding the laboratory part and inbetween the laboratory parts, subjects will
wear a watch, which registers activity and light exposure profiles.