Biological Rhythms

2 positives of Michel Siffre (1975) research

Siffre's study was also an experiment - he controlled key variables (exogenous zeitgebers) to observe the effects on his sleep-wake cycle. This allowed the demonstration of causal relationships. However, subsequent studies above ground have confirmed the findings of research in cave environments.

What happens as he person enters deep sleep

), their brainwaves slow and their breathing and heart rate decreases.

Homesotatic control of the Sleep-Wake cycle

- When we have been awake for a long period of time, homeostasis tells us that the need for sleep is increasing because of the amount of energy used up during wakefulness. - This homeostatic drive for sleep increases gradually throughout the day, reaching its maximum in the late e

When does our strongest sleep drive occur between?

2-4 am and 1-3pm

How long is a sleep cycle?

90 minutes

Entrainment

An adjustment of the body clock in line with the environment

Four Categories of Brain Wave Ptterns

Beta Alpha Theta Delta

Circadian Rhythms

Biological rhythms that last about 24 hours and are set/reset by environmental light levels.

Folkard et al (1985)

Conducted an experiment to see if external cues could be used to override the internal clock. A group of 12 people (18-21 yrs) lived in a temporal isolation unit for three weeks, isolated from natural light and other time cues, except a clock. These volunteers agreed to go to bed when the clock indicated 11.45pm and to get up when it indicated 7.45am. Initially, for the first 4 days, the clock ran normally, but gradually they quickened the clock until it was indicating the passing of 24 hours when actually only 22 hours had passed. At the beginning the volunteers' circadian cycle matched the clock but as it quickened their rhythm ceased to match the clock and continued to follow a 24-hour cycle rather than the 22-hour cycle imposed by the experiment (except for one participant who did adapt to the 22-hour cycle).

Dement and Kleitman (1957) Procedure

Connected 9 participants (7 males; 2 females) to an EEG machine in a lab, which took measurements throughout a night's sleep.

3 steps of the Temperature Cycle

Core body temperature rises to its highest at about 6pm (38 degrees Celsius) and falls by about 2 degrees Celsius over the next 10 hours to a low at about 4.30am. During the normal circadian rhythm, sleep occurs when the core temperature begins to drop and alertness increases as body temperature starts to rise in the last few hours of sleep. There is a slight drop in body temperature in the afternoon (2-4pm), which could explain feelings of sleepiness. This could affect cognitive behaviours e.g. alertness, memory.

Which hormone helps with alertness?

Cortisol, increasing about an hour before a person wakes up

Evaluation of research into the sleep-wake cycle Individual differences in the sleep/wake cycle

Cycle length: research has found that circadian cycles can vary anywhere from 13 to 65 hours (Czeisler et al., 1999). Cycle onset: individuals appear to be innately different in terms of when their circadian rhythms peak....

Exogenous zeitgebers

Environmental cues, such as light, that help to regulate the biological clock in an organism

Dement and Kleitman (1957) Findings

Everyone had periods of REM every night. There were high incidences of dream recall when participants are awakened during REM sleep. If awakened in the other stages, very few reported dreaming. The brain activity of very vivid dreams was different to the less clear dreams. The rapid eye movements of REM sleep varied according to dream type and mirrored brain activity whilst awake and completing a similar task to the one they had dreamt about.

Real World Applications example of Chronotherapeutics and what does this show?

For example, you are at greatest risk of having a heart attack in the early hours of the morning. Aspirin would therefore be most effective if taken at around 11pm, as it takes between 2-4 hours to peak in the blood stream. This shows a clear practical implication for research on biological rhythms

The __________ system tends to make us sleepier as time goes on throughout the waking period, regardless of whether it is night or day.

Homeostatic system

Hormone production follows what kind of rhythm?

Hormone release follows a circadian rhythm. For example, the production and release of melatonin from the pineal gland in the brain follows a circadian rhythm, with levels peaking during the hours of darkness and decreasing in response to light in the morning.

Evaluation of research into the sleep-wake cycle Research Methodology

In most studies, although participants were isolated from variables that might affect their circadian rhythms, such as clocks, radios and daylight, they were not isolated from artificial light because it was thought that dim artificial light, in contrast to daylight, would not affect their circadian rhythms... Therefore, artificial light could have confounded research findings when estimating the 'free running' nature of the human circadian rhythm.

Endogenous pacemaker

Internal body 'clocks' that regulate biological rhythms

What happens in the process of photoentrainment

Light-sensitive cells within the eye act as brightness detectors, sending messages about environmental light levels direct to the SCN. The SCN then uses this information to coordinate the activity of the entire circadian system. For example, if light levels are low, the SCN communicates with the pineal gland to secrete melatonin.

What hormone encourages sleep?

Melatonin

What are the first four stages of sleep called?

NREM sleep (non-rapid eye movement

Research evidence to support differences between the circadian temperature rhythm and circadian sleep-wake cycle Hawkins and Armstrong-Esther (1978)

Nurses on shift duty were able to adjust their sleep-wake cycle quite quickly to their shift pattern, but their temperature cycle took at least a week to change.

Aschoff & Wever (1976)

Participants were placed in an underground WWII bunker, in the absence of any environmental and social time cues. They found that most participants displayed circadian rhythms between 24 & 25 hours in length, although some rhythms were as long as 29 hours. This shows that the cycle operates in the absence of external cues and that the natural free-running cycle is about 24-25 hours.

Dement and Kleitman (1957) Criticisms

Participants were studied in a sleep laboratory. This could have caused an atypical reaction from ppts. The frequency of occurrence of REM sleep might be different in a non-experimental setting

Sleep stages consists of what two kinds of sleep

REM and NREM

What is the fifh stage of sleep called?

REM sleep (rapid eye movement).

The Sleep-Wake Cycle: Research Evidence Michel Siffre (1975)

Siffre (a French cave explorer) spent 6 months in a cave with no natural light or cues as to the day or time e.g. clocks or radio. He simply woke, ate and slept when he felt it was appropriate to do so and his internal body clock was allowed to free-run. It settled into a sleep/wake cycle of 25-30 hours. He lost track of how many days he had been in the cave, believing it to be one month less than he had actually stayed in. This suggests that circadian rhythms persist despite isolation from natural light, which demonstrates the existence of an endogenous clock i.e. his SCN continued to regulate his sleep-wake cycle. However, it also shows that external cues are important in terms of keeping the sleep-wake cycle in sync with the outside world, because his clock was not exactly 24 hours.

Two examples of Ultradian rhythms

Sleep stages Basic-activity rest cycle (BRAC)

What are 3 examples of circadian rhythms?

Sleep-wake cycle Temperature cycle Hormone production Our body clock is regulated by an internal system including such factors as release of hormones like melatonin, metabolic rate and body temperature

The Sleep-Wake Cycle

The circadian rhythm not only dictates when we should be sleeping, but also when we should be awake. Levels of light and darkness are the external signals that determine when we feel the need to sleep and wake up. The circadian rhythm dips and rises at different times of the day.

2 negatives of Michel Siffre (1975) research

The study of Michel Siffre is a case study and therefore has unique features. His body's behaviour may not be typical of all people. Living in a cave may have particular effects due to, for example, the fact that it is cold.

What does Folkard et al's (1985) research suggest about circadian rhythms?

They can only be guided to a limited extent by eternal cues

Real World Applications Chronotherapeutics

This is the treatment of an illness or disorder by administering a drug/treatment at a time of day believed to be in harmony with the body's natural rhythms i.e. at a time when it will be more effective. For example, you are at greatest risk of having a heart attack in the early hours of the morning. Aspirin would therefore be most effective if taken at around 11pm, as it takes between 2-4 hours to peak in the blood stream.

Why is the circadian temperature rhythm different from the circadian sleep-wake cycle?

as they both peak at different times, thus there must be at least two biological clocks.

How are stages of sleep measured

by the electrical activities of the brain, with each stage showing a distinct EEG pattern.

The _________ system keeps us awake as long as there is daylight

circadian

Biological Rhythms

cyclical changes in the way the biological systems behave

Evaluation of research into the sleep-wake cycle Czeisler et al (1999) found

found evidence to demonstrate the influence of artificial light on the sleep-wake cycle: They altered participants' circadian rhythms down to 22 hours and up to 28 hours by using dim artificial lighting alone.

2 factors that impact the sleep-wake cycle

jet travel and shift work, as they cause the biological clock e.g. the SCN (and the physiological systems that are dependent on this e.g. the sleep-wake cycle) to become completely out of sync with the outside world.

The internal circadian clock is described as "Free running"

means that the sleep-wake cycle will maintain a cycle of about 24-25 hours, even in the absence of external cues.

Evaluation of research into the sleep-wake cycle Individual differences in the sleep/wake cycle Duffy et al (2000)

morning people ('larks') prefer to rise early and go to bed early (about 6am and 10pm)... whereas evening people ('owls') prefer to wake and go to bed later (10am and 1am).

What important things happen in Deep Sleep

most of the body's physiological 'repair work' is undertaken and important biochemical processes occur i.e. the production of growth hormones.

Friedman and Fisher (1967) BRAC support

observed the eating and drinking behaviour in a group of psychiatric patients over a period of 6 hours and found a 90 minute cycle in eating and drinking behaviour, thus adding support to the BRAC.

The Basic Rest Activity Cycle (Kleitman, 1969)

referred to the 90-minute cycle of sleep as the Basic Rest Activity Cycle (BRAC) He suggested that this ultradian rhythm continues during the day, even when we are awake: we move progressively from a state of alertness into a state of physiological fatigue ~ every 90 minutes Research suggests that the human mind can focus for a period of ~90 minutes and towards the end of these 90 minutes the body begins to run out of resources, resulting in loss of concentration, fatigue & hunger.

What happens in the 5th stage of sleep?

the EEG pattern resembles that of an awake person and it is in this stage that most dreaming occurs.

Suprachiasmatic nucleus (SCN)

the master circadian pacemaker, found in the hypothalamus.