MODULE 5: NON-PHOTIC TRAINING IN HUMANS Flashcards
Aschoff and Wever’s WWII bunker experiment allowed for subjects to live in ___ isolation for weeks/months
isolation
what was confirmed in Aschoff and Wever’s WWII experiment? (2)
humans have true circadian rhythms that persist in constant conditions
appear to entrain to a daily LD
people who were entrained to a gong sound that reinforced the LD cycle provided evidence that.. (2)
humans are less sensitive to light as a time cue
social cues might be the primary zeitgeber
in subsequent experiments, allowed no access to the time of day nor contact with the outside.. using an overhead light as their light source what did experimenters expect?
that they would entrain to the overhead light
in subsequent experiments, allowed no access to the time of day nor contact with the outside.. using an overhead light as their light source what actually happened?
subjects free-ran with a tau >24h
Czeisler found that when subjects were allowed to use a reading lamp when the overhead lights were off each day that..
it gave subjects the potential to create their own LD cycle
after re-examination of the issue that human LD cycles are not sufficient enough to entrain.. Czeisler found that..
if an LD cycle was strictly enforced, subjects did entrain
previously discusses methods are barely used to investigate circadian rhythms, why? (2)
it takes weeks/months to test each subject
requires substantial subject commitment
what 2 main questions are typically being asked?
do humans free-run in constant conditions?
do humans entrain to LD?
what is the faster procedure to answer these questions?
the constant routine method
recall: briefly describe the constant routine method
subjects cannot get out of bed
are fed at regular intervals
what are the 2 benefits of using the constant routine method?
eliminates the masking effects of behaviour/LD transitions
allows repeated measures of core body temp/melatonin/cortisol
the removal of ___ effects and ____ sampling provides and accurate assessment of the ___&____ of the rhythms being measured
masking
frequent
phase & period
which rhythm is not affected by the sleep-wake cycle and is a product released by the pineal gland?
melatonin secretions
describe melatonin levels throughout the day
rises in the evening/prior to sleep onset
peaks in the middle of the night
falls in the morning
the secretion of melatonin is rapidly ___ by light
supressed
when using a constant routine method in dim light what are the rise/fall of melatonin in the evening/morning called?
evening: dim light melatonin onsets
morning: dim light melatonin offsets
describe the procedure when investigating if light can induce phase shifts in humans while using the constant routine method
- subjects sleep 3 nights in the lab
- undergo a 30h constant routine
- sleep from 12-8pm
- stay awake all night
during the staying up all night period: after how long is a light pulse introduced?
6h
after staying up all night, subjects will sleep again from 12-8pm where after they undergo..
the 2nd constant routine method for a full day
what 2 things are sampled and their peaks are compared during which part of the procedure?
melatonin
body temp
during the constant routine parts
when comparing the peaks of melatonin and body temp during the constant routine parts, it was found that..
light induced a large delay shift
midpoint of melatonin was phase delayed by 3.6h during the 2nd constant routine
is a phase response curve in humans the same shape as PRC in animals?
yes
light early in the subjective night causes a..
phase delay
light in the late subjective night causes a..
phase advance
when do we see the crossover from delays to advances?
at the body temperature minimum which is about 3 hours before a spontaneous wakeup
what is the deadzone? is this present in nocturnal animals?
a time that occurs in the middle of the subjective day
may be absent in nocturnal animals
introducing light before the minimum body temperature causes a..
phase delay
when do we see the crossover from advances to delays?
about 12h before or after the body temperature minimum
is there an extended period during the subjective day like the deadzone?
no
introducing light after the minimum body temp causes..
a phase advance
what subjects can be used when looking for non-photic regulation of circadian rhythms?
those who lack visual function
someone can be blind but still have ..
retinal photoreceptors that respond to light and can communicate the LD cycles to the brain
some people can have no conscious vision and are unable to discriminate light/dark BUT can show ___ responses to light exposure
neuroendocrine
neuroendocrine responses are still evident how?
measuring melatonin concentrations in the blood/saliva
describe the control of melatonin’s secretion
via the pineal gland under the control of the circadian clock
what are the 2 effects light has on melatonin?
entrains the circadian clock that consequently controls melatonin release
rapidly inhibits melatonin synthesis and release
when light inhibits melatonin synthesis and release, is that dependent or independent on the circadian clock?
indepedent
turning on a light in the middle of the night (sleeping) causes..
a suppression in melatonin synthesis and a rapid reduction of plasma melatonin concentration
how is light information communicated to the pineal gland and how is the circadian clock in the hypothalamus entrained?
via photoreceptors in the retina
how can we distinguish between a totally blind or just visually blind person?
the melatonin suppression response to light exposure
if a blind person still shows light-induced melatonin suppression they are ____ blind
visually
a positive melatonin suppression result means the person is …
not circadian blind
a negative melatonin suppression result means..
the person is circadian blind and they cannot entrain LD cycles
what does DLMO stand for?
dim light melatonin onset
what is DLMO?
the time when the level of melatonin reaches 25% of the maximum value that it can eventually exhibit
using 2 blind individuals: they underwent a 2 day constant routine every 20-30 days where experimenters measured..
their melatonin rhythms and their DLMO
using 2 blind individuals: they underwent a 2 day constant routine every 20-30 days: being exposed to light pulses allowed experimenters to determine if they retain ____
circadian photoreception
the individual who did not show melatonin impression in response to light showed a __________ in their actogram
progressive shift of DLMO across their tests
was the person who showed no melatonin suppression free-running despite the attempt to maintain a 24h sleep-wake cycle?
yes
people who tend to be circadian blind typically report..
being unable to fall asleep or have trouble staying awake in the day
the individual who did show melatonin suppression showed a _____ DLMO near their bedtime
rountinely
the person who showed melatonin suppression showed ___ photic entrainment and can be distinguished as..
normal
visually blind
melatonin as a ___ can entrain rhythms
drug
____ melatonin can shift circadian rhythms
exogenous
___ melatonin provides a measurement of rhythms
plasma
___ melatonin has a circadian rhythm
endogenous
what would someone intuitively think about blind people and non-photic cues?
they would be more sensitive to non-photic time cues
blind people lacking photoreceptors normally ____ while maintaining a 24h work schedule does not allow non-photic stimuli to have much or any effect
free-running
blind people might have more difficulty doing what?
entraining to 24h non-photic cues
the circadian clock in blind people is 0.4h ___ than those in sighted people
slower
describe the limit of/range to entrainment
PRC to light pulses show that circadian rhythms can only be shifted a small fraction of a single circadian cycle per cycle
the period of a LD cycle must be within ___h of tau for LD to entrain the clock
1-3
using a ___ zeitgeber causes ___ shifts and a smaller ___ of entrainment
weak
smaller
range
non-photic ____ should be more effective for sighted people than the circadian blind
zeitgebers
what is an important source of potential non-photic zeitgebers?
social interactions
alarms, parents, breakfast, physical activity, or showers are all examples of non-photic sources that can cause..
internal/endocrine signals that can affect the circadian clock
co-housing people in temporal isolation was done to see if..
sleep-wake and other rhythms remain synchronized as a group or if each person free-runs with different periodicities
after 10 days of bright light and 10 days of dim light bedtimes became..
more variable
what was observed from the co-housing temporal isolation experiment?
people can ignore social cues and follow their own circadian cycle
after the co-housing temporal isolation experiment: what is there to be said about social synchrony?
might be mediated by light exposure and not by non-photic stimuli
studies are done in the artic because..
it is continuously light for part of the summer
in the artic studies: subjects were observed to ..
free-run independently of each other
in the artic studies: starting off with gathering for communal meals led to what.. because of independent free-running
eventually eating different meals at the communal meal time
when isolating potential non-photic zeitgebers, one needs ________
controlled lab experiments
studies were done examining the effects of 1h of high-intensity exercise on _____
phase of melatonin secretion rhythm
in the high-intensity exercise study: what method was used to measure the first couple of cycles following the exercise stimulus?
constant routine method
in the high-intensity exercise study: what were the 4 circadian phases that exercise was scheduled at?
night
morning
afternoon
evening
in the high-intensity exercise study: ____ shifts were observed and the direction was dependent on the ____ of the exercise
small
time
in the high-intensity exercise study: when did advanced shifts occur?
following early evening exercise and only on the first day following the exercise
in the high-intensity exercise study: when did delay shifts occur?
following exercise in the night or morning or afternoon
in the high-intensity exercise study: why are the results not super convincing?
the shifts are small and the phase advances were only evident on day 1 after exercise
describe the non-24h T-cycle paradigm
- subjects live on a 23.66 day with or without 2 scheduled bouts of exercise during their daily wake time
- t-cycle: period of the zeitgeber bring manipulated
- wake period light levels are dim
in the non-24h T-cycle paradigm: what days were melatonin rhythms measured /averaged?
days 1/8/14
in the non-24h T-cycle paradigm: the no exercise group showed a __ in melatonin rhythm relative to their daily bedtime
delay
in the non-24h T-cycle paradigm: the exercise group’s melatonin rhythm on day ___ was closer to its day 1 position
14
in the non-24h T-cycle paradigm: the execise group’s results showed that..
exercise did help the clock advance
in the non-24h T-cycle paradigm: what was the methodological weakness?
the light was dim and not the same as in DD thus exercise could potentially increase light input and be responsible for daily advances
manipulation of _____ alone without scheduled exercise has little effect on circadian rhythm
sleep-wake timing
describe the experiment of the independent sleep-wake effect
subjects kept in dim light and fed at 4 fixed mealtimes went to bed at 9pm each day and were kept awake until 11:30pm on the first night
subsequent nights: experimental group could sleep 20 mins earlier each day for 7 days
measured bodily melatonin and temperature during constant routines before and after the 7day sleep-wake schedule
in the independent sleep-wake effect study: describe the experimental group’s results
melatonin and temperature rhythms did not advance but they fell asleep earlier
in the independent sleep-wake effect study: describe the control group’s results
kept the 24h sleep schedule and showed a delay of their temp/melatonin levels
in the independent sleep-wake effect study: which schedule prevented the clock from phase delaying?
experiemental
can the sleep-wake cycle shift the clock?
yes but it is a weak zeitgeber
___ is a model used to investigate the effects of meal timing
Ramadan
in Ramadan: when is food eaten for one month each year?
after sunset
why can nothing be concluded from Ramadan studies?
so many stimuli are changed simultaneously
describe how lab studies concluded that a food being a zeitgeber in humans is rare
eating a big breakfast or dinner for 3 days phase advanced the body temp rhythm but not the DLMO
the DLMO is a ____ circadian clock phase maker in humans
gold-standard
if the DLMO did not shift, the ___ probably did not shift
circadian clock
circadian clocks in ___ are influenced by non-photic stimuli but the observed effects are ___ in contrast to rodents
humans
weak
social cues are ___ and likely mediated by ______
weak
exercise/arousal//feeding
exercise bouts can _____ but are modest in size
induce shifts
exercise in the night or early morning can cause..
small delay shifts
exercise in the early evening can cause..
phase advance shifts
daily exercise can facilitate entrainment to _____ sleep-wake cycles and ____ to shifted sleep-wake cycles
unusual
re-entrainment
scheduled sleep-wake cycles have ___ effects when light exposure and ___ are controlled
weak
meal timing
the available data on ___ is too sparse to make any meaningful conclusions
food
