Disrupting Circadian rhythms
Jet Lag and Shift Lag
Aims
To know the symptoms of Jet Lag
To understand the effects of jet lag upon biological rhythms
To be able to understand the effects on the SCN of
disruptions to EP and EZ co-ordination
Key concepts
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SCN disruption
EP and EZ De-synchronisation
Performance decrement
One day to adjust for every hour of time change
East to West is best – Phase Delay
West to East is a beast – Phase Advance
Melatonin treatment
Fasting
The consequences of Jet Lag
• Jet lag
When travelling to different parts of the world, for
some days after the journey,
The Sleep/Wake cycle is disrupted
The Body temperature changes
Other symptoms;
– Daytime sleepiness, fatigue,
– difficulty concentrating, headache, irritability, gastric discomfort,
and trouble initiating and maintaining sleep.
#SCN is disrupted
East to west is
best
Social customs
sleep when
supposed to
eat when
supposed to
Food can reset
some
biological
clocks
PD
Melatonin
Jet
Lag
Alcohol coffee
can have a
cumulative
effect in
disruption
Bright
light/artificial
light
Fasting then
eat on new
time schedule
BASE BALL
STUDY
Cause
We can fix the disruption by using:
Melatonin
Food
And Bright light (phototherapy)
Task: SCN Disruption
• Complete the following diagram; labelling
– SCN
– Cannot cope with sudden changes
– Dorsal
– Ventral
– Protein synthesis (CLK+BLMAL1)
– Negative feedback loop
Ventral SCN influenced by external cues (Light)
Dorsal SCN less affected by light
Disrupting the SCN (s)
• The neurons of the ventral SCN are now believed to function not
so much as clocks but rather as the location in the SCN that
receives and responds to external inputs,
• while the neurons of the dorsal SCN are believed to constitute
the SCN’s actual robust, endogenous clock. This view is
supported by certain jet-lag experiments which have shown that
in rats, the process by which a light stimulus resets the internal
clock occurs far more rapidly in the ventral SCN than in the
dorsal SCN.
• Scientists have now discovered that the neurotransmitter GABA
excites the cells of the dorsal SCN but inhibits those of the
ventral SCN. These opposing effects might influence the differing
reaction times of these two sub-regions when someone travels
across several time zones. This discovery thus opens new insights
into the mechanisms behind the disturbing symptoms of jet lag.
• Ventral SCN influenced by external cues (Light)
• Dorsal SCN less affected by light
• 1 hour of time change = 1 day to adjust
Phase delay = delay sleep
Phase advance = sleep earlier
Jet Lag
• If you travel by plane from (East to West) UK to USA leaving
at 12:00 noon, you will arrive at 7:00 pm UK time when it is
actually 2.00pm USA time.
• So, by 7:00 pm in the US, your biological clock is 12:00
midnight.
• All your biological rhythms are working on UK time. Your
internal clock is telling you that it is midnight and you are
ready to fall asleep.
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Melatonin is released,
body temperature drops
bodily arousal decreases
• Jet Lag is the time it takes to adjust and resynchronise
• The quickest way to adjust is to follow the local EZ’s (Phase Delay)
delay sleep and stay up later.
• If you follow your EP (UK time) it will take longer to adjust – leading
to more severe symptoms of Jet Lag.
East to west, e.g. UK to USA
PHASE
DELAY
Easier to Adjust
PHASE
More difficult to Adjust
advance
West to east e.g. USA to UK
East to west is always best!
• Phase delay – east to west e.g. UK to Mexico –
we gain time. It is easier to lengthen our day
(Siffre study, shift work research). Biologically
ahead of local time – stay up later.
• Phase advance – flying east means the day is
shortened, this is difficult to adjust to and
symptoms of jet lag will be worse – go to bed
earlier.
Circadian rhythms that adapt more slowly
cope best with Shift Lag/Jet lag
Other individual differences: ………………………….
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Unhappy and happy shift workers
Your conclusion is ...
Treatment
• Research: Melatonin has been studied to treat
jet lag and other desynchronisation problems
(Takahashi et al., 2002)
What can we do?
• Blakemore 1988 found that a synthetic version
of melatonin administered in the evening can
reduced jet lag symptoms.
• Melatonin is available in USA and research is
being carried out to see if it can be used to
help aircrew.
• Read the case study p176. What are the
problems of using melatonin to treat jet lag?
Write a summary of the Melatonin and Aircrew
research studies. P.163/176 Eysenck
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No large enough clinical trials to evaluate long term effects
Melatonin can help clock to adjust
Use Melatonin only if you are in the time zone for 3 days
Scientists claim that Melatonin use for Aircrew is inappropriate
Re-synchronisation occurs only if ppt allowed to sleep after taking
Melatonin
• Melatonin’s effect on motor and cognitive function is still
unknown (the sedative effects are still unknown)
• Research is on going: US air force actively investigating its
usefulness, aircrew participating in in exp. Study are not allowed
to fly within 36 hours
• Melatonin receptors are present on the
neurons of the suprachiasmatic nuclei of most
species. This suggests that the secretion of
melatonin is regulated by a negative feedback
loop. Experiments in which the administration
of exogenous melatonin affected the circadian
rhythm of locomotor activity in various
rodents have also shown that this hormone
can affect the functioning of the body’s
biological clock.
Harma et al. (1994)
and Suvanto et al. (1993)
• Harma et al. (1994) and Suvanto et al. (1993) examined the
effects of a four day flight that crossed 10 time zones on the
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Sleep
Alertness
Attentiveness
Body temperature
Salivary melatonin of the flight attendants
• Forty female attendants logged their subjective sleepiness and
sleep quality each day. Their
– Alertness
– Visual task performance
– Melatonin level
– Body temperature was
monitored every 2 hours
• They found that they became sleepier over the 4 days and had
less sleep. Their cognitive ability varied too. Melatonin and
body temperature delayed by almost 4 hours after the
westward flight.
Fasting
BBC Jet Lag
Stop eating
• Fasting is the key
http://www.bbc.co.uk/science/humanbody/
DMNH – Dorsal Medial
Nucleus of the Hypothalamus
The FEO
(Food entrainment Oscillator)
• Scientists have long known that our circadian rhythm is regulated by
our exposure to light. Now they have found a second "food clock" that
takes over when we are hungry. This mechanism probably evolved to
make sure starving mammals don't go to sleep when they should be
foraging for food.
• The lead researcher Clifford Saper explains:
• The neat thing about this second clock is that it can override the main clock...and
you should just flip into that new time zone in one day.
• It usually takes people a week to fully adjust to a new time zone or
sleeping schedule. To think that this new "food clock" hack can help
you change your internal clock in one day is mind boggling.
DMNH – Dorsal
Medial
Nucleus of the
Hypothalamus
The FEO
(Food entrainment
Oscillator)
This will influence
circadian rhythms
when organism is
starved for
12-16 hours
How Do You Use This Trick?
• Simply stop eating during the 12-16 hour period before you want to be
awake. Once you start eating again, your internal clock will be reset as
though it is the start of a new day. Your body will consider the time you
break your fast as your new "morning."
– For example, if you want to start waking up at 2:00 am, you should
start fasting between 10:00 am or 2:00 pm the previous day, and don't
break your fast until you wake up at 2:00 am. Make sure you eat a nice
healthy meal to jumpstart your system.
– Another example: If you are travelling from Los Angeles to Tokyo,
figure out when breakfast is served in Tokyo, and don't eat for the 1216 hours before Tokyo's breakfast time.
• Combined with other hacks to help you get more sleep and be more
productive, you can quickly adjust to any time zone.
Video clip: Fasting
• http://www.wisebread.com/how-to-naturallyreset-your-sleep-cycle-overnight
Klein, Wegman and Hunt’s “Westbound” flights
study (1972) Found that the adjustment of the
sleep-waking cycle was faster when flying
westbound.
As the natural timeclock is 25 hours, it seems to
be easier to have a longer day (phase delay)
than 'back' in time (Phase disruption.)
Evaluation of research on disrupting
biological rhythms
• Research findings
Disrupting our biological rhythms has cognitive and
emotional effects, as well as drastic consequences
• Methodological issues
Studies have great ecological validity, however personality
and individual differences are not controlled in those
studies
• Real-life significance?
Does it matter? Effects on cognitive abilities, such as
attention and concentration negatively influence our
intellectual and emotional well-being
Hw
• Describe the human endogenous pacemaker
(biological clock) in control of the sleep wake cycle
(6m).
• Describe one study of circadian rhythms (8m).
• What application to the real world has biological
rhythm research got? (4m)
• Explain individual difference effects on Circadian
Rhythm research (8m)
• Discuss research and explanations of the
disruption of Circadian rhythms (16m) AO2/3
Evaluation/commentary