Biological Rhythms Flashcards
Biological rhythms
Repetitive biological processes that happen internally
3 different types of bio rhythms
Ultradian
Circadian
Infradian
Ultradian cycles
Occur multiple times in 1 day and are ultra quick
Example: blood circulation
Circadian cycles
Occur once a day
Also known as sleep cycle
Infradian cycle
Occur in cycles longer than a day: can range from across multiple weeks/ months
Example: Menstruation
What drives bio rhythms?
Factors that are
Exogenous (occur in the environment such as light)
Endogenous (occur internally such as with the release of hormones)
Key research
Czeisler
Where and who did Czeisler study?
153 male potash factory workers in Utah
In Czeislers study, what was the original schedule for the workers?
85 worked rotational phase advancing shifts
68 worked non rotating day/swing shifts
Phase advance
when you have to bring FORWARD in the day the time you go to bed
Aka going to bed early
A phase advance rotational shift means…
Workers would have a shift earlier than previously; working in night then working in afternoon then working in morning
So they’d go to bed EARLIER = advance circadian rhythm
Phase delay
When you bring BACKWARD in the day the time you go to bed
Aka going to bed later
First questionnaire Czeisler handed out to factory workers
Asked about happiness, productivity and opinion on their current shifts
How many workers on the rotational shift had previously fallen asleep at work? (From Czeislers 1st questionnaire)
29%
Czeisler’s intervention
Gave presentation to managers + workers
Suggests 85 rotational shift workers change to investigate:
All had phase delay shift but divided into 2 groups:
Rotate 7 days
Rotate 21 days
Czeisler’s second questionnaire
About workers new happiness, health and preferences with the new schedule they were assigned: all phase delay but some rotated 7 days compared to 21 days
What did post intervention find out?
Significantly preferred phase delay
Significantly happier rotating every 7 days than 21 days
21 phase delay = significantly happiest and healthiest compared to any other schedule
Czeisler’s 9 month analysis
Analyse productivity and turnover; long term effects of his intervention
Czeisler’s 9 month analysis findings
The turnover for non rotating shift workers was the same for 21 phase delay rotating shift workers
Conclusion of Czeisler
To minimise the impacts of disrupted circadian rhythms:
Disrupt the rhythm less frequently
Disrupt by phase delay (rhythm occurs later in the day) is preferred because we have 25 hr internal clock
Additional research
Siffre - living underground
Preckel - investigate effect of sleep schedules on academic performance
Melatonin
Light boxes
How did Siffre complete his investigation?
Lived in a cave for 2 months to control for exposure to exogenous cues
Called research team to report when he had woken up, his eating habits, his blood pressure reading (collected data in these forms)
What did Siffre aim to investigate?
To measure the body’s internal sleep cycle (circadian rhythm) by isolating it from all exogenous cues such as seasons, light, temperature, knowledge of time etc
Siffre’s conclusion
The body followed a 25 hour sleep-wake cycle
Suggesting humans have an independent 25 hour body clock, which is independent of exogenous terrestrial cycles
What did Preckel aim to investigate?
Investigate the effect of German high school students sleep cycles on their academic performance
Preckel’s sample
272 German high schoolers
What is a chronotype?
A theory that someone can favour going to bed and waking up early (lark chronotype)
Or going to bed and waking up late (owl chronotype)
Preckel’s procedure
Gave a chronotype questionnaire to students (find out if they’re an ‘owl’ or ‘lark’
Give standardised cognitive test
Give questionnaire to parents to find out their academic habits; motivation, conscientiousness etc
Why did Preckel give a survey to the high schooler’s parents and the cognitive test to the students?
So he could collect data on the individual differences across the sample, such as cognitive ability, motivation and conscientiousness that may affect grade
Preckel’s findings
After isolating the variable of chronotype, having an owl chronotype is a negative predictor of maths and language GPA
Application to Preckel?
Start colleges and schools later so those with owl chronotype are not at a disadvantage
Melatonin
Hormone secreted in pineal gland to induce sleep
Activated by exogenous cues: darkness, and when someone knows the time is late (time sense)
Melatonin supplements
Provide boost of melatonin to go to feel sleepy (makes someone go to bed earlier)
When should someone use melatonin supplements?
To go to bed earlier eg phase advance of their sleep-wake cycle
How can melatonin in the Uk be obtained?
Only via prescription from a GP
Light boxes
Artificial boxes of light that sitting in front of for 15 mins a day will keep someone awake for
Because it uses light as an exogenous cue to prevent pineal gland releasing melatonin
When should someone use a light box?
To go to bed later eg phase delay of sleep wake cycle
