MODULE 4: NON-PHOTIC ENTRAINMENT Flashcards
what is typically known to be the dominant zeitgeber in synchronizing circadian rhythms to local time?
light
what other 3 kinds of cues are animals exposed to that could reflect zeitgebers?
external/geophysical
biotic
internal
in the 60s/70s humans were believed to only be weakly sensitive to which zeitgeber?
light
how does social stimuli contribute to light zeitgeber?
regulates exposure to light
what 2 ways can social stimuli influence entrainment via regulating light exposure?
- independently affect the clock via sight/smell/sound/contact
- interactions could affect behavioral state and the neural circuits that control the sleep-wake cycle
if ___ can affect the clock,
then potentially anything ___ could shift circadian rhythms
behavioural state
arousing
what is the concept of the generic black-box model?
intended to represent various elements/interactions thought to be present in the brain/body to explain circadian rhythms
the box represents what in the generic black box model?
the circadian clock
in the black-box model: LD cycles are shown to..
create non-photic cycles
what is considered the “input” of the black-box model?
retina
light exposure is seen to be controlled by what 2 things?
- clock
2. social stimuli
how does the clock contribute to light exposure control?
generates the daily sleep-wake cycle
how does social stimuli contribute to light exposure control?
control the sleep-wake states
why is there speculation that behavioral states contribute to light exposure?
- brain area interactions are reciprocal
2. principle of brain organization suggests that brain areas controlled by the clock may send feedback to the clock
what is the most obvious approach to test if social stimuli affect circadian rhythms independently
study young animals who are dependent on parenting for food and warmth
in rats: when does the circadian clock begin to cycle?
in utero before birth
how is a rat’s clock being entrained in utero?
via signals from the mother
what signals are sent to the rat in utero from its mother to entrain to local environmental time?
pineal gland hormone melatonin
food intake
how are rabbits and post/neonatal rats entrained to local environmental time?
daily milk-meal provided by its mother
explain the evidence for social synchrony in beave families
- use of gnawing on wood as an indicator of wake
- there was evident unitary free-running circadian rhythm during the winter
- all family members were active at the same time
what is the conservative interpretation of the beaver social synchrony experiment?
familiy members bring active at the same time represents social synchrony
what is the concern with the conservative interpretation?
the dominant member might mask the true phases of the rest-activity rhythms in subordinate members
bats live in ___ and a study in India observed that bats became active ____ in synchrony prior to ___
true caves
en masse
nightfall
bats would wake up…
at sunset the bats would …
prior to sundown
start foraging
out of night light exposure and social stimuli cues, which cue is critical and which one is sufficient?
night light exposure: critical
social cues: sufficient
if a bat was kept in a cage and was prevented from flying, did it remain entrained to the outside world even with no light exposure?
yes
if a bat was caged but with no other bats, did it remain synchronized?
no it free-ran
can one officially establish that social stimuli affect the animal’s rest-activity cycle and brain areas?
no
Mrosovsky concluded ____ are not needed to induce a phase shift
social stimuli
in Mrosovsky’s syrian hamster experiment: presenting an intruder into a resident hamster’s cage at what time caused an advance shift?
subjective day
in Mrosovsky’s syrian hamster experiment: presenting an intruder into a resident hamster’s cage at what time caused a small delay or no shift?
subjective night
what was the 2nd arousal technique that stimulated the activity of investigating/scent markings/rearrangement?
changing the cage litter
did changing the cage litter induce phase shifts like the intruder condition?
yes
how was a phase shift measured in the experiment where: a hamster was put on a novel wheel after LD entrainment and then DD for 4 days and then be returned to its home cage
comparing the activity onset on the 2nd day of DD and during the LD period
true or false - in hamsters: social cues are special as zeitgebers?
false
what is believed to cause clock shifts?
some correlate of being awake or continuously active
can a clock be shifted by an animal’s behaviour?
yes
____ can alter the period of circadian rhythms
acute stimulation of activity
Mrosovsky tested the effects of 3h bouts of___ scheduled at 12 different phases of the circadian rest-activity cycle in hamsters
novel wheel induced running
exercise in the middle of the ___ caused larger advance phases
subjective day/their rest phase
exercise in the middle of the ____ caused small delay shifts
subjective night/their active phase
using light pulses on Syrian hamsters showed advance and delay zones but what was different about them?
they occurred at radically different timings
the circadian clock was shifted by light at ___ when it should be awake
night
the circadian clock was shifted by exercise in the __ when it was supposed to be sleeping
day
stimuli occurring at the wrong time of day is seen as..
an error interpreted by the circadian clock
a ___ is required to re-establish the appropriate phase relationship between the hamster/environment
phase shift
if a bout of exercise can ____ and the non-photic PRC is ___, then a __ should be capable of entraining free-running rhythms
induce a phase shift
bidirectional
daily exercise
a mouse kept in DD with an open running wheel but having it locked for 12h each day lead to ..
a gradually entrained free-running drinking rhythm
blind mice were forced to run on the treadmill for 3h each day which led to..
entrainment of the free-running drinking rhythm
both ___ and ___ running behaviour induces phase shifts that are sufficient enough to entrain free-running rhythms
voluntary and forced
mice free-running with a tau < 24h required a daily ____ to entrain to a 24 hour exercise schedule
phase delay
at what time was it predicted that exercise should be induced so mice (<24h tau) would entrain?
subjective night
mice free-running with a tau > 24h required a daily ___ to entrain to a 24h exercise schedule
phase advance
at what time was it predicted that exercise should be induced so mice (>24 tau) would entrain?
beginning of subjective night > middle of subjective day
what is the concern with exercise on a novel wheel being the behavioral stimulus causing phase shifts?
a locked wheel caused no shift because the hamster would fall asleep
how would experimenters keep a hamster up for 1-3 hrs?
by appearing and blowing a puff of air or touching them
3h arousal with little locomotor activity was sufficient enough to induce a ___ shift
advance
____ correlates of exercise are not the stimuli that shifts the clock
neural or endocrine
hamsters that were kept awake for 3h but did not phase shift were..
more stressed by the procedure
those that were kept awake using more stressful procedures had blood samples with high ___ levels
cortisol
some neural or endocrine correlate of stress can _____ the phase-shifting effect of arousal
supress
if behavioural arousal participates in entrainment in natural environments, then its effects must be strong enough to ________ in the presence of LD cycles
alter circadian rhythms
hamsters entrained to LD cycle and placed in a novel wheel in the middle of light period for 2 weeks showed..
large delay in the timing of its nocturnal activity
switching from LD to DD and the animal was left undisturbed for 10 days resulted in the unexpected activity that..
activity stimulated in the middle of the subjective day in DD causes phase advances not delays
the interaction between non-photic arousal stimulus and LD cycle produced a
non-linear outcome
why are nocturnal animals unexposed to light for 14 hours in the day?
the sleep in dens during the day
what is the skeleton photoperiod?
30 mins of light representing the sunrise and 30 mins of light representing the sunset
nocturnal animals entrain stably to ___ although weaker than full photoperiods
skeleton photoperiods
a hamster entrained to the skeleton photoperiod and placed in a novel wheel for 3h a day in the middle of its subjective day led to..
a shift in nocturnal activity where there was a phase invert and its subjective night is now reflected by its subjective day bevaiour
a light pulse being presented in the late subjective night caused..
no disturbance
a hamster put into a novel wheel and ran during light pulse caused ..
no shift
exercise can ___ the phase-shifting effect of light
inhibit
behavioural arousal with or without exercise can ___ circadian clock and ___ actions of the light on the clock enough to alter the phase of entrainment to LD
shift
inhibit
exercise and ____ of arousal can induce phase shifts, entrain, and alter free-running tau
a correlate
female rodents have a 4-5 day estrous cycle where ..
they will accept a mate and be proactive in seeking one
voluntary running altering free-running tau is puzzling, why?
might make entrainment to LD cycles more precise
in mice/rats: light presented in the evening causes the clock to ..
delay
in mice/rats: running in the subjective night causes
an advance phase by shortening tau
the opposite effects of light and exercise allow activity onset to..
be very close to nightfall
hamsters are more responsive to…. than mice/rats which means ..
single bouts of light/exercise
non-photic effects are powerful but differ between species
circadian rhythms are sensitive to daily variations in __ and __ availablility
food
water
in laboratory conditions: food is provided freely through the 24h day but nocturnal rodents eat primarily.. but nibble..
at night
in the day
hamsters kept in LL for 2 months led to..
slowing the circadian clock to lengthen free-running tau
prolonged/very bright light can lead to..
dampening or loss of circadian rhythms
rats kept in DD or dim light and restricted to 3h food access per day have free-running activity rhythms that..
do not entrain to daily feeding schedules
what are the 2 daily rhythms rats exhibit
- free-running rhythm evident prior to restricted feeding that continues to run
- bout of activity occurring each day immediately prior to meal time
simultaneous occurrence with different periodicities suggest there are 2 circadian clocks.. what are they?
- light-entrainable pacemaker
2. food-entrainable pacemaker
describe the light-entrainable pacemaker
normally entrains to LD cycles and free runs in DD or LL
describe the food-entrainable pacemaker
entrains to daily feeding cycles
how can the food anticipatory activity rhythm be induced?
by the natural progression from satiety to hunger
which timing mechanism could control the food anticipation?
metabolic hourglass timer
describe how the stomach would work as an hourglass timer?
being stuffed with food after a meal and gradually empties over a number of hours
recall: stopwatches can be used to measure intervals of..
any duration
describe the fixed interval reinforcement schedule
reward is received for an operant response but further responses go unrewarded until a time interval has passed
the fixed interval reinforcment schedule makes rats…
remember the duration of the interval between rewards
rats exhibit timing behaviour with ___-like properties
stopwatch-timing
food anticipation might not be controlled by a circadian clock but by an_____ analogous to a stopwatch
interval timer
interval timers can time one cycle but must be reset to time the next.. if daily rhythms of food anticipatory were controlled by an interval timer, then .. (3)
- rhythm should stop if a scheduled meal is omitted
- rhythm should appear regardless of the duration of the feeding interval
- rhythm should reset immediately if mealtime is shfited
if the food anticipatory rhythms are controlled by a food-entrainable clock, then.. (3)
- the rhythm shoudl persist in constant conditions
- rhythm should only appear if the feeding schedule is in the circadian range
- the rhythm should reset gradually rather than immediately if mealtime is shifted
what evidence is there that a food-entrainable clock can explain the daily food anticipatory activity rhythms?
- food anticipation rhythms persist in constant conditions
- food anticipation rhythm has circadian rhythms to entrainment
- if mealtime is shifted, the FAA shifts gradually rather than immediately
- FAA does not require the light-entrainable circadian pacemaker
what are the 3 temporal niches?
diurnal, nocturnal ,crepuscular
food anticipation in rats fed during usual rest phase demonstrates..
temporal niche switching
a switch to diurnality occurs when ..
food is limited to daytime
can niche switching occur for even if food is restricted to the daytime ?
yes
mice showed that too high of a workload led to
less eating and a shift of nocturnal to dirunal
the shift in mice from nocturnal to diurnal was established by.. (3)
- less activity at night and body temperature dropped
- when a lot of energy is needed to obtain food, animals will eat less and save energy by decreasing body temp at night
- LD cycle is predictive in daily variations in environmental temp that would be predictive in nature
