Effects of an afternoon stroll under different light conditions on alertness, sleep quality and -perception

Sunlight is considered to be one of the primary zeitgebers in humans for
entraining the circadian clock. Light can phase-shift endogenous oscillator in
the Suprachiasmatic Nucleus and in this way synchronize internal rhythms with
environmental day-night cycles.
The activity of the SCN changes over the course of the day and night. During
the day, when ipRGCs are activated by different amounts and wavelengths of
light, SCN activity is high, coinciding with relatively high levels of
alertness and suppression of the nocturnal hormone melatonin occurs. During the
night, in absence of light, there is less SCN activity, coinciding with a
decrease in alertness and an increase in melatonin concentrations.
Sleep is regulated by an interaction of homeostatic and circadian processes.
This is commonly described by the two process model, which states that sleep is
regulated by a homeostatic component, which tracks how much sleep is needed,
and a circadian process, which determines when to sleep. The two processes
together influence sleep architecture, timing, duration and quality. EEG is
often used as a measurement to determine sleep, as brain frequencies measured
reflect different stages of sleep. Sleep can be devided in four phases, three
stages of non-REM and one stage of REM.
Nowadays, many experiments have been conducted to investigate the clock
shifting properties of light, resulting in either a phase advance or delay,
depending on subjective time of the individiual. However, less is known about
the influence of light on the homeostatic sleep pressure. Previous research
suggest a positive effect of sunlight exposure on alertness and subjective
sleep duration and sleep quality. Other experiments conducted by the
Chronobiology unit of the University of Groningen also suggest a link between
light exposure and sleep architecture, indicating a modulation of light on the
homeostatic sleep drive. Activity has also been determined to have positive
effects on sleep. A general assumption is that an evening constitution has a
positive effect on sleep.

To investigate whether three hours of consecutive daylight and activity can
affect alertness and improve night-time objective and subjective sleep.

The study has a within the individual design and will be performed in the
field.
Participants will spent the first evening at home under dim light conditions
(curtains closed while wearing some blue light blocking orange glasses) to
determine dim light melatonin onset. This is necessary to determine phase angle
of entrainment, to make sure that the light exposure does not cause a change in
phase and therewith affects sleep. DLMO will be determined with the help of 5
saliva samples, taking every hour, starting 6 hours before habitual sleep time
(determined by the Münich Chronotype Questionnaire).
There is a strong correlation between DLMO and core body temperature. The
relation between core body temperature minimum and DLMO was derived from
previous work and is found to be CBT¬min=(DLMO-20)*1,25+317. From each CBTmin
can the individual deadzone of each participant be calculated. As a true
deadzone does not exist for humans, the afternoon constitution will be centered
around this deadzone, with 1.5 hour in the phase advance portion and 1.5 hour
while being exposed to light while causing a phase delay. On the day of DLMO
determination, subjects are asked to refrain themselves from cafeine,banana's
and chocolate.

Thereafter, subjects will take part in this experiment two times, separated by
exactly one week. Both times, they will walk for three consecutive hours while
being exposed to natural light. One time they will wear neutral density
filtered glasses (for the whole duration of the stroll), the other time not.
Which treatment is allocated at which time will be randomized.
Participants will come to the university of Groningen 30 minutes before they
have to start their afternoon stroll. They will receive actiwatches on the
non-dominant wrist to check whether they indeed walked for the allocated amount
of time and to gain insight about the intensities of light that they have been
exposed to. In addition, they will wear light watchers on a cord around their
neck to determine the spectral composition of the light that they*ve been
exposed to.
After the three hour walk, which can be on a self-selected route, participants
will come back to the university of Groningen (which has to be the start and
end point of the walk, so data can be checked immediatly by the investigator).
Here they will hand in their actiwatch and light watcher. Actiwatch data will
be checked immediately, to ensure that participants followed protocol.
If this is the case, subjects are allowed to go home. 6 hours before habitual
sleep onset, they again have to sit in de dim light, to perform another DLMO
determination. This is done to check whether the intervention indeed has not
shifted the clock. During this DLMO determination, the investigator will visit,
to attach electrodes to the participants, which will be placed on the following
positions: EOGL, EOGR, EMG, Cz, C3, C4, Fpz and Oz. A reference electrode will
be placed at the left mastoid. After DLMO determination, subjects are allowed
to go to sleep while wearing Camtech Actiwave loggers to determine EEG
activity. Upon awakening, they will fill in a questionnaire concerning sleep
quality and alertness. Thereafter, the investigator will come by again to
remove the electrodes and loggers. One week later the same protocol will be
repeated with the other intervention.

There are no risks associated with participation, as light conditions used are
conditions that we are regularly exposed to in every day life.
A possible burden for participants might be that they have to walk for 3
consecutive hours independent of the weather. This can be experienced as
unpleasant. Also, subject have to refrain themselves from caffeine, banana's
and chocolate on days on which they have to perform a DLMO (three times in
total). This can be experienced as unpleasant.