Biopsychology: Circadian rhythms Flashcards
What are biological rhythms?
All living organisms, plants, animals and people are subject to biological rhythms and these influence how body systems behave.
All biological rhythms are governed by two things
- The body’s internal biological clocks: Endogenous pacemakers.
- External changes in the environment: Exogenous zeitgebers.
What is a circadian rhythm?
A type of biological rhythm that lasts for 24 hours and changes body processes e.g. sleep/wake cycle and core body temperature.
What is the sleep/ wake cycle?
The sleep-wake cycle has a recurring pattern, as it oscillates between wakefulness and sleeps in a 24-hour clock. On a healthy sleep-wake rhythm, humans spend approximately eight hours sleeping and sixteen hours awake. The role of the sleep-wake cycle is to regulate our sleep at night and keep us awake during the day.
Our biological clocks are present in every cell, synchronised by the suprachiasmatic nucleus (SCN), located in the hypothalamus. Genes produce proteins that continuously increase throughout the night while we sleep but reduce during the day. These fluctuations activate the sleep-wake cycle.
The SWC is governed by internal and external mechanisms which are:
- Exogenous zeitgebers: We feel drowsy when it’s nighttime and alert during the day. This demonstrates the effect of daylight.
- Endogenous pacemaker: If the biological clock was left to its own devices without the influence of external stimuli such as light, it’s called free running.
What is Siffre’s case study: circadian rhythms?
Michael Siffre spent long periods underground with no radio clocks etc. He simply woke, ate and slept when he felt like it. After his first underground stay of 61 days in the Southern Alps, he resurfaced on September 17th thinking it was August 20th
What was Aschoff and Wever’s study (1976)?
Aschoff and Wever (1976) found that participants who spent 4 weeks in a bunker without natural light showed circadian rhythms of 24-25 hours, except for one participant who went up to 29 hours. This suggests the natural circadian rhythm is slightly shortened by the effects of daylight.
What is core body temperature: circadian rhythms?
Body temperature is another circadian rhythm. Human body temperature is at its lowest in the early hours of the morning (36oC at 4:30 am) and at its highest in the early evening (38oC at 6 pm). Sleep typically occurs when the core temperature starts to drop, and the body temperature starts to rise towards the end of a sleep cycle promoting feelings of alertness first thing in the morning.
A03: Circadian rhythms
+ Research support
+ RLA
- Individual differences
- Poor control
A03: Circadian rhythms: Research support
Research has been conducted to investigate circadian rhythms and the effect of external cues like light on this system. Siffre (1975) found that the absence of external cues significantly altered his circadian rhythm: When he returned from an underground stay with no clocks or light, he believed the date to be a month earlier than it was. This suggests that his 24-hour sleep-wake cycle was increased by the lack of external cues, making him believe one day was longer than it was, and leading to his thinking that fewer days had passed.
A03: Circadian rhythms: Individual differences
However, it is important to note the differences between individuals when it comes to circadian cycles. Duffy et al. (2001) found that ‘morning people’ prefer to rise and go to bed early (about 6 am and 10 pm) whereas ‘evening people’ prefer to wake and go to bed later (about 10 am and 1 am). This demonstrates that there may be innate individual differences in circadian rhythms, which suggests that researchers should focus on these differences during investigations.
A03: Circadian rhythms: RLA
One real-world application of circadian rhythms is chronotherapeutics - the study of how timing affects drug treatments.
The specific time that patients take their medication is very important as it can have a significant impact on treatment success. It is essential that the right concentration of a drug is released in the target area of the body at the time that the drug is most needed. For example, the risk of heart attack is greatest during the early morning hours after awakening, and so chronotherapeutic medications have been developed with a novel drug delivery system. These medications can be administered before the person goes to sleep at 10 pm, but the actual drug is not released until the vulnerability period of 6 am to noon.
A03: Circadian rhythms: Poor control
Artificial lighting could be an extraneous variable as could be impacting the sleep/wake cycle even though researchers thought it has no impact. Czesler et al. adjusted participants circadian rhythms from 22-28 hours using dim lighting. This means that artificial lighting could reset the biological clock. This suggests research has ignored an important confounding variable.
