Biopsychology : Circadian Rhythms Flashcards
What are biological rhythms?
Cyclical patterns within biological systems
The circadian rhythm?
Daily cycles (Circa → around, Dian → day. Eg, sleep wake cycle)
The infradian rhythm?
Cycles lasting longer than one day (eg. Menstrual cycle)
The ultradian rhythm?
You have multiple of the cycles a day (eg. REM sleep)
What are endogenous pacemakers?
Internal mechanisms that govern biological rhythms (e.g. pineal gland)
What are exogenous zeitgebers?
External mechanisms that govern biological rhythms (e.g. light and dark)
What is the relationship between EPs and EZs?
There are cycles affected by both endogenous pacemakers and entrained by exogenous zeitgebers. For example, the sleep wake cycle is a biological rhythm (endogenous) but is also affected by daylight (exogenous).
The Sleep-wake cycle : What’s SCN?
The supra-chiasmatic nucleus is a major endogenous pacemaker in mammals that controls the sleep wake cycle. It’s in the hypothalamus where the optic nerves from the eye cross over. It’s stimulated by light that penetrates out closed eyelids then regulates the sleep wake cycle.
The Sleep-wake cycle : What’s the process of the sleep-wake cycle?
SCN passes info on day length and light it receives to pineal gland. Pineal gland increases melatonin production (induces sleep). Sunlight in the morning stops the production of melatonin and increases the production of cortisol which increased wakefulness.
The Sleep-wake cycle : What’s homeostasis?
the maintenance of constant internal environment. It tells the body there’s a need for sleep when its been awake too long. The homeostasis drive for sleep increases throughout the day, reaching max in late evening (NOT a circadian rhythm)
The Sleep-wake cycle : What’s an example of a circadian rhythm?
Body temperature → lowest (36°) at 4:30AM and highest (38°) at around 6:00PM. Sleep occurs when the core temp begins to drop and the body temp starts to rise during the last few hours of sleep, promoting a feeling of alertness in the morning.
Michel Siffre’s (1975) Cave study - Aim
to investigate how the human body’s natural circadian rhythms behave in the absence of external cues such as natural light, sound and temp fluctuations (to determine whether the body’s internal clock could maintain a regular sleep wake cycle without exogenous zeitgebergs)
Michel Siffre’s (1975) Cave study - Procedure
Siffre isolated himself in a cave for 6 months, devoid of natural life and external time cues (no access to clocks, sunlight or other indicators of time). The cave environment was kept constant, with controlled temp and humidity levels. He communicated with researchers outside the cave via telephone and recorded his sleep-wake cycles, body temperature and psychological state while external researchers monitored his activities remotely.
Michel Siffre’s (1975) Cave study - Findings
siffre’s sleep wake cycle extended from 24h to 25h meaning a day lasted 25 hours and lead his sleep and waking times drifted later each day. When he returned, he believed it to be a month earlier than it was but other than that his body remained regular.
Michel Siffre’s (1975) Cave study - Conclusion
the human body has an intrinsic circadian rhythm which is naturally longer than 24hrs but external cues like natural light play a crucial role in resetting the internal clock to align with the 24 hour day.
Aschoff and Wever (1976)
Convinced P’s to spend 4 weeks in WW2 bunker deprived of light, all displayed circadian rhythm of 24-25hrs apart from one (29hrs)
Folkard
Conducted a study of circadian rhythms similar to Siffre, in a cave. They had a clock that enforced strict bed and waking times but Ps didn’t know researchers sped the clocks so their days were only 22hrs. Only 1 P could comfortably adjust
Consequences of desynchronisation - What is it?
Occurs when an individuals internal body clock s out of sync with the external environment
Consequences of desynchronisation - Jet-Lag
caused by travelling across time zones. The internal clock isn’t synchronised with the day time- night time rhythm at the place of arrival. Social cues are involved, adapting to local times for eating and sleeping (rather than responding to internal feelings of hunger and fatigu
Consequences of desynchronisation - Shift work
causes desynchronisation in circadian rhythm which in turn leads to negative health effects. Regulated by social cues, such as social interactions with others, meal times, work schedules
Consequences of desynchronisation - Infants sleep wake cycles
newborns sleep wake cycles can be random and desynchronised. The circadian rhythm begins around 6 weeks and is entrained at around 16 weeks, by adult schedules of mealtimes and bedtimes.
Circadian rhythm studies - Animal evidence
Ralph (1990) bred a group of hamsters to follow a 20hr circadian cycle. SCN cells were removed and transplanted into the brains of rat foetuses w normal rhythms. When born, they had 20hr sequences. Then their brains were transplanted with SCN cells from 24hr hamsters and within a week their cycles were 24hrs. When cells from the SCN were removed from the rats the 24hr cycle remained in the isolated cells, suggesting that circadian rhythms are primarily controlled by evolutionarily determined biological structures that exert a strong influence on us to maintain normal sleep-wake patterns.
Circadian rhythm studies - Tissue evidence
Yamazaki (2001) found that isolated lungs and livers and other tissues grown in a lab still show circadian rhythms, suggesting cells are capable of maintaining a circadian rhythm even when they’re not under the control of the brain and that bodily cells are tuned in to follow a daily rhythm
Circadian rhythm studies - Inuit sleep cycle
Inuit Indians, who live in the Arctic Circle, in an environment with almost no darkness in summer and no light in winter, maintain a fairly regular pattern of sleep-wake all year around. If the sleep-wake cycle was primarily controlled by
EZ’s they would tend to sleep a huge amount in winter and hardly at all in summer.
Strengths for circadian rhythms…
• Animal data supporting SCN as a crucial endogenous cycle → DeCoursey et al (2000) destroyed the SCN connections in the brains of 30 chipmunks and observed them in their natural habitat for 80 days. The researchers found that the chipmunks’ sleep-wake cycles disappeared, and a significant proportion of them were killed by predators (because they were asleep and vulnerable when they should have been awake). Severe ethical issues (is it justified?).
• Supporting evidence that exogenous zeitgebers influence circadian rhythms → Campbell and Murphy (1998) exposed 15 Ps to light on the back of their knees at various times. This intervention managed to shift their sleep-wake cycles by up to 3 hours, suggesting that light can influence circadian rhythms independently of visual input.
• Understanding negative effects of sleep-wake disruption → Boivin et al. (1996) investigated the sleep-wake cycles of night shift workers and found a circadian trough around 6 a.m., where concentration significantly decreased, increasing the likelihood of mistakes and accidents. Furthermore, shift workers are three times more likely to develop heart disease (Knuttson, 2003)), highlighting the serious health risks associated with circadian rhythm disruption.
• Contribution to chronotherapeutics (timing meds to align w body clock) → Bonten et al. (2015) demonstrated that taking aspirin at night is most effective at reducing the risk of heart attacks, statistically more likely to occur in the morning due to the body’s circadian processes that increase blood pressure and heart rate upon waking
Limitations for circadian rhythms…
• Methodological problems w Siffre’s study → In Siffre’s Cave Study there was a lack of control as he used an artificial light when in the cave. This could have confounded the results as other research has shown circadian rhythms can be adjusted as a result of dim lighting. Also, he was also the researcher and the p, which means experimenter bias could have been present.
• Evidence the main exogenous zeitgeberg for sleep wake cycle is temp not light → Buhr et al. (2010) found that fluctuations in temp set the timing of cells in the body and caused tissues and organs to become active or inactive. Buhr claimed that info about light levels is transformed into neural messages that set the body’s temp.
• Importance of individual differences overlooked (chronotypes) → Duffy et al. (2001) found ‘morning people’ prefer to rise and go to bed early (about 6 am and 10 pm) and ‘evening people’ prefer to wake and go to bed later (about 10am and 1am).
• Small sample sizes lead to generalisability issues → Studies of the sleep/wake cycle often use small groups of participants (eg Aschoff & Wever) or even single individuals (eg Siffre).
