So according to the AQA specification, you need to know the following;

“Biological rhythms: circadian, infradian and ultradian and the difference between these rhythms. The effect of endogenous pacemakers and exogenous zeitgebers on the sleep/wake cycle.”

Some of you will be grateful to know that this is the last part of biopsychology that you need to know about in this unit. Spoiler alert! There will be some more biopsychology being brought into later topics, but this will be embedded within other theories and ideas.

Breaking down what the quote from the specification above says you need to be able to do the following:

1. Describe, recognise and use your knowledge of the 3 biological rhythms (Circ/ Infr/ Ultr)
2. Evaluate or discuss the  influence of these rhythms regarding human behaviour
3. Describe, recognise and use your knowledge of endogenous pacemakers and exogenous zeitgebers
4. Evaluate or discuss the influence of endogenous pacemakers and exogenous zeitgebers on biological rhythms and/ or human behaviours

Basically, even though this is the last part of the specification, it is probably one of the bigger parts too, as there is so much you need to be able to describe and also evaluate. The good news is however, that research evidence and evaluations that you have for one you can use for others in the same, or a different way. I would recommend before you think about evaluating these you make sure you have a really strong understanding of how they all work, as this will make the discussion and application of this knowledge much more manageable and achievable!

Right so lets get started!

Biological Rhythms

Most of the earths living organism are exposed to some form of day and night and also seasons. As a result of that, our bodies have evolved to make the most out of certain times of the day or year and developed to help us cope with other times. As I’m sure you are now aware from the previous learning throughout biopsychology, our biological processes and our behaviours are intricately connected. We can definitely find at least a relationship between some processes and behaviours, in some cases even a direct cause and effect can be identified. Which is why it makes sense that when our bodies respond the changes in the environment, so does our behaviour.

These are the biological rhythms we are talking about:

Biological rhythms are cyclical patterns within biological systems that have evolved in response to environmental influences, e.g. day and night.

There are two key factors that govern biological rhythms: endogenous pacemakers (internal), the body’s biological clocks, and exogenous zeitgebers (external), which are changes in the environment.

There are 3 types of biological Rhythms:

1. Circadian- run in 24 hours cycles
2. Infradian- run in cycles lasting longer than 24 hours
3. Ultradian- run in cycles lasting shorter than 24 hours

We will cover all of these in detail over the rest of this page by looking at how they work, research that supports this and the influence internal and external factors have on them all.

Circadian Rhythms

The first main biological rhythms you need to know about is Circadian Rhythms. These run in 24 hours cycles– Starting at sunrise, running all the way through that day’s sunset then a new cycle starting again at the following sunrise. Our bodies are trained to respond to the changes in light to ensure optimal survival. If we were nocturnal we would have more of a chance of being hurt, injured or killed in the wild as everything we did to survive would occur at night time. Think of it from an evolutionary perspective;

To understand this, we have two cave men- Bob and Dave.

Dave’s biology tells him when the sunrises he needs to wake up. He isn’t tired anymore, he feels hungry and he will leave his really cosy furskin blanket and warm cave to find food for him and his cave babies. Once he has had a long day hunting and providing shelter for his family, Dave retreats to his cave for a good 8-10 hours sleeps before he repeats the same process again.

Eat, Sleep, Rise, Repeat! 

Dave on the other hand, doesn’t have this biological process yet, his father didn’t pass it onto him genetically. So he sleeps through most of the day- then wakes up around 10pm when on a warm summer day the sun is setting.

By the time Dave is up and out of his cave it is pitch black outside. He stumbles around looking for an animal to hunt and plants to pick but nothing is around and even if they were, there is no electricity so Dave can only see as far as his hand (it’s a cloudy night so the moon isn’t shining as much). What happens to Dave and his cave family next?

Well 1 of the following could happen;

1. Dave falls off a cliff to his eventual demise, his cave babies never receive food and eventualy die too.
2. Dave gets eaten by a bigger more dangerous animal, his cave babies never receive food and eventually die too
3. Dave returns with very little food, all of them eventually starve and die out

If we think back to the evolutionary approach, whose genes are more likely to be passed on?

Bob of course! He is able to safely provide food and shelter for himself and his offspring, is able to continue reproducing and therefore passing on his survival genes of responding to the sunset and sunrise and as a result his children will have the gene and so will be able to the same. And so this evolutionary process continues into modern day!

We call this the Sleep- Wake Cycle. This is an example of the main circadian rhythm our bodies follow. The waking up when the body is exposed to light (sunrise) and the sleepy feeling when light is reduced (sunset) is your body telling when to sleep and when to be awake.

So how does this happen? 

As you already know, sensory information is sent from our peripheral nervous system (our entire body apart from the brain and spinal cord) using receptor cells. These receptors cells identify information and pass that onto the brain to be processed, which will then tells us the appropriate behaviour for the environmental situation we are in.

In this instance, an increase in light is processed by receptor cells in our eyes and also our skin. This sends a messages to the suprachiasmatic nuclei (SCN) located in the Hypothalamus. The SCN then uses this information to activate the Pineal Gland to release or inhibit Melatonin. This makes you feel sleepy and cools down your body temperature. When there is an increase in light, your pineal gland will stop producing melatonin, when there is a decrease in light your pineal gland will start producing melatonin.

Endogenous Pacemakers & Exogenous Zeitgebers

Biological rhythms are regulated by endogenous pacemakers, which are the body’s internal biological clocks, and exogenous zeitgebers, which are external cues. These help to regulate the internal biological clocks/ rhythms like the one you just read about.

Endogenous pacemakers are internal mechanisms that govern biological rhythms, in particular, the circadian sleep-wake cycle. Although endogenous pacemakers are internal biological clocks, they can be altered and affected by the environment.
The most important endogenous pacemaker is the suprachiasmatic nucleus, which is closely linked to the pineal gland, both of which are influential in maintaining the circadian sleep/wake cycle.

The suprachiasmatic nucleus (SCN), which lies in the hypothalamus, is the main endogenous pacemaker (or master clock). It controls other biological rhythms, as it links to other areas of the brain responsible for sleep and arousal. The SCN also receives information about light levels (an exogenous zeitgeber) from the optic nerve, which sets the circadian rhythm so that it is in synchronisation with the outside world, e.g. day and night.

As outlined above, exogenous zeitgebers influence biological rhythms: these can be described as environmental events that are responsible for resetting the biological clock of an organism. They can include social cues such as meal times and social activities, but the most important zeitgeber is light, which is responsible for resetting the body clock each day, keeping it on a 24-hour cycle.

The SNC contains receptors that are sensitive to light and this external cue is used to synchronise the body’s internal organs and glands. Melanopsin, which is a protein in the eye, is sensitive to light and carries the signals to the SCN to set the 24-hour daily body cycle. In addition, social cues, such as mealtimes, can also act as zeitgebers and humans can compensate for the lack of natural light, by using social cues instead.

Can you think of any other examples of exogenous zeitgebers which affect when we wake up and when we feel sleepy? 

This is how I remember which is which:

Endogenous Pacemaker-a Pacemaker is something that is inserted into a persons chest to regulate their heartrate, it works internally. It’s an internal system.

Exogenous Zeitgeber- ZeiT= ouTside?

I appreciate these are loose connections but it’s the only way I’ve managed to remember which way round they are. If you can think of a better memory cue I am all ears!

Research into Circadian Rhythms

Michel Siffre spent 7 months in a cave deep underground with no natural light and no change in temperature

Why?

To see how his body and behaviour would react to the lack of natural light. He found that his sleep wake cycle changed from 24 hours to a 25 hour cycle.

Watch this video to get more details about this experiment

Link to an article summarising the effects of a reduced circadian rhythms on rats mental and physical abilities

Evaluation: Circadian Rhythms

When you are asked a 16 mark question on circadian rhythms, they will either ask you:

• Discuss research into circadian rhythms (16). This will mean that you need to use GRAVER to evaluate the research.

Generalisability: A weakness of research into circadian research, like mentioned above is that they lack generalisability. For example, Siffre’s research was a case study involving one participant. Often other studies will only involve a small group of participants to allow for the in-depth studying of biological statistics that is required of research into the circadian rhythms. As a result, findings reflect only those participants’ personal individual differences, such as their motivation to be isolated and bodily history, therefore the findings cannot be generalised across to the wider public as easily to make wide sweeping conclusions about circadian rhythms and how they work.

Validity: One of the strengths of research into circadian rhythms is their high internal validity. Aschoff & Weber studied participants living in a bunker. The bunker had no windows and only artificial light, which the participants were free to turn on and off as they pleased. As a result of being conducted in artificial settings which have been highly controlled, we are able to more confidently assume direct cause and effect of the environment in the bunker and the impact on the circadian rhythm.  

Reliability: The research had good reliability. Additionally, psychologists such as Siffre were able to record and follow standardised procedures which would allow for the research to be replicated and assessed for consistency of results. In Siffre’s case he has conducted this procedure multiple times, resulting in the same results. As a consequence, we can be more confident that the change in his circadian rhythms and our conclusions about how the sleep wake cycle works, is based on the changes in the environment. 

Validity issues – extraneous variables: However, in Siffre’s study, it is also worth noting that although natural light sources had been removed by hiding underground, artificial light from torches and cameras have been shown to reset endogenous pacemakers, therefore counting as unaccounted extraneous variables. Some may argue that this conflicts with internal validity of the research and others like it. Conflicting with the conclusions previously assumed to be correct.

Applications: Whilst research into the sleep wake cycle can be questionable for many reasons, one of the strengths is the information that can be used for positive impacts in the real world. For example, there are many jobs which require people to work in opposition to a natural sleep wake cycle which research has shown can have a negative impact on biological and behavioural responses. By using our knowledge of how our EZs and EPs work together we can support people who work night shifts to ensure they do not suffer the effects of a disturbed sleep wake cycle. As a result of being proactive rather than reactive, this will aim to reduce the impact on the NHS when treating people suffering from the physical and mental health difficulties that can be caused by working unsociable hours.

• Discuss the role of endogenous pacemakers (internal) on circadian rhythms (16). This will involve you creating arguments as to the extent to which EP’s play a role in influencing the circadian rhythm, and this opens the opportunity to discuss how EZ’s also play a role. 

Useful applications: There are practical applications to drug treatments when understanding EP’s. Circadian rhythms co-ordinate a number of the body’s basic processes such as heart rate, digestion and hormone levels. This in turn has an effect on pharmacokinetics, that is, the action of drugs on the body and how well they are absorbed and distributed. Research into circadian rhythms has revealed that there are certain peak times during the day or night when drugs are likely to be at their most effective. This has led to the development of guidelines to do with the timing of drug dosing for a whole range of medications including anticancer, cardiovascular, respiratory, anti-ulcer and anti-epileptic drugs (Baraldo 2008).

Individual differences: within our sleep wake cycles could suggest that EPs have a large impact on our sleep- wake behaviours. Duffy et al (2001) found ‘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). Within time zones, everyone experiences the same sun rise and sun set cycle which, if we assume EZs are more influential than EPs, would suggest everyone wakes around the same time and everyone sleeps around the same time. When we see these individual differences it could be concluded our EPs might be wired differently from one another and that these differences might overwrite the influence of any EZs. Suggesting that EPs play more of a role in dictating when we sleep and when we wake. Although it is important to recognise that research shows both are relevant for maintaining a healthy circadian rhythm.

Research to support: There has been research conducted to suggest that endogenous pacemakers are free running and do not need the use of exogenous zeitgebers to maintain a sleep- wake cycle. For example, Siffre (1962) spent 7 months in a subterranean cave without any natural light or changes in temperate. He was isolated from any other person and had nothing to indicate the start or end of a day. As a result, he maintained a sleep-wake cycle of 25 hours suggesting that our bodies are not dependent on the presence of light to be able to maintain a cycle, and that endogenous pacemakers play a significant role in these cycles. However, it is also important to recognise that the cycle did change from 24 hours to 25, suggesting that whilst our EPs will run regardless of the influence of EZs, they still need the external sources to ensure it stays within the timeframe of a circadian rhythm (24 hours).

Research to support: Folkard (Clock) – see above!

• Discuss the role of exogenous zeitgebers (external) on circadian rhythms (16). This will involve you creating arguments as to the extent to which EZ’s play a role in influencing the circadian rhythm, and this opens the opportunity to discuss how EP’s also play a role. 

Research to support: There is research to support the impact of of exogenous pacemakers on the circadian rhythms. 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 (exogenous zeitgebers), making him believe one day was longer than it was, and leading to his thinking that fewer days had passed. Challenge: On the other hand, Siffre’s case study has been the subject of criticism. As the researcher and sole participant in his case study, there are severe issues with generalisability. This weakens the support of circadian rhythms as we cannot be certain that everyone’s body clock would be effected in the same way. 

Research to support: However, further research by Aschoff & Weber (1962) provides additional support for the impact of exogenous zeitgebers. Aschoff & Weber studied participants living in a bunker. The bunker had no windows and only artificial light, which the participants were free to turn on and off as they pleased. Aschoff & Weber found that the participants settled into a longer sleep/wake cycle of between 25-27 hours. These results, along with Siffre’s findings, suggest that humans use natural light (exogenous zeitgebers) to regulate a 24-hour circadian sleep-wake cycle, demonstrating the importance of light for this circadian rhythm.

Individual Differences: Another problem with assuming that EZ’s impact individuals circadian rhythm in the same way, is that it doesn’t account for individual differences. 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, as the exogenous zeitgeber of light for people within the same time zone, would assume to be the same. Therefore, differences between these two types of ‘people’ aren’t explained by sunrise and sunset. As a consequence, this suggests that Exogenous Zeitgebers aren’t as influential as originally thought, and individual differences that are biologically based have more of an impact on our circadian rhythm. 

Alternate explanations & Holism: Additionally, it has been suggested that other EZ’s such as temperature may be more important than light in determining circadian rhythms. Buhr et al. (2010) found that fluctuations in temperature set the timing of cells in the body and caused tissues and organs to become active or inactive. Buhr claimed that information about light levels is transformed into neural messages that set the body’s temperature. Body temperature fluctuates on a 24-hour circadian rhythm and even small changes in it can send a powerful signal to our body clocks. This shows that circadian rhythms are controlled and affected by several different factors, and suggests that a more holistic approach to research might be preferable.

Useful applications: There are practical applications in understanding EZ’s on circadian rhythms.  For instance, night workers engaged in shift work experience a period of reduced concentration around 6 in the morning (a circadian trough) meaning mistakes and accidents are more likely (Boivin et al. 1996). Research has also suggested a relationship between shift work and poor health: shift workers are three times more likely to develop heart disease (Knutsson 2003) which may in part due to the stress of adjusting to different sleep/wake patterns and the lack of poor quality sleep during the day. This is useful because knowledge of the influence of EZs on circadian rhythms can give individuals a better understanding of the adverse consequences that can occur as a result of their disruption and evidence based tools to increase a healthier circadian rhythm, hinged on environmental changes (e.g blackout blinds, reduction of noise, reduced temperatures). Thus, research into the sleep/wake cycle may have economic implications in terms of how best to manage worker productivity by understanding the impact of EZs and reducing the health implications for the NHS. 

https://www.ted.com/talks/russell_foster_why_do_we_sleep watch this ted talk and make notes on the health benefits of getting a good night sleep. What would we advise people who frequently suffer from dysregulated sleep wake cycles (Shift workers/ night workers/ jet lag). How could they ensure they are getting optimum sleep and also why would this a wider benefit on society? What institution is going to benefit if less people have these health issues? 

Infradian Rhythms 

Another important biological rhythm is the infradian rhythm.  Infradian rhythms last longer than 24 hours and can be weekly, monthly or annually. 

Two examples of these are: 

• The Menstrual Cycle 
• Seasonal Affective Disorder

The Menstrual Cycle

We are going to focus on this one as it’s probably the most familiar to you, having studied it during GCSE Biology. In understanding this process, it’s really important to remember that this is like a chain reaction of hormones. If one hormone isn’t released at the right point or in the right concentrations then the next step won’t happen and it throws the whole ‘machine’ out of sync. 

Video describing the biological process of the Menstrual Cycle

Biological Process of Menstrual Cycle (Word Document) 

You can either watch the video above or you can follow my attached word document explaining the process. Both resources should be used in conjunction with the following graphs that chart the different endogenous pacemakers that contribute towards it. 

Once you have a solid understanding of the biological processes (Endogenous Pacemakers), have a think about the when the following changes in hormones and why the behavioral consequences happen when they do: 

1.Slight increases in oestrogen and progesterone = heightened sense of smell, clearer thinking and better coordination, feeling of a new beginning

2.Surges in LH= more energy and increased sex drive

3.Start of decreasing progesterone= bring on anxiety, depression, irritability and mood swings.

Exogenous Pacemakers of the Menstrual Cycle

• Stress 
• Diet 
• Other peoples pheromones

If you body is in Fight or Flight, as with digestion, its main focus is going to be for survival not reproducing. Therefore you hypothalamus focuses on organising the body to prepare to run or stand and fight and stops anything that requires energy to continue the menstrual cycle. 

Click here to get a reminder of what fight or flight is

Pheromones are chemical substances that released through sweat and are picked up (unconsciously) by our receptors in our noses and send information to the Olfactory parts of our brain (areas that deal with smell and taste- which is why you can sometimes taste a smell, because they are processed in the same area). There is a theory that if womens periods and therefore ovulations are at the same time, they will give birth around the same time and be able to share the child rearing to ensure optimal survival of the communities offspring. 

Evaluation of Infradian Rhythms

When you are asked a 16 mark question on circadian rhythms, they will either ask you:

Discuss research into infradian rhythms (16). This will mean that you need to use GRAVER to evaluate the research.

Validity: One weakness is that research such as this is difficult to establish high internal validity. Russell et al. (1980) found that female menstrual cycles became synchronised with other females through odour exposure. In one study, sweat samples from one group of women were rubbed onto the upper lip of another group. Despite the fact that the two groups were separate, their menstrual cycles synchronised. However, other variables such as diet, exercise and stress levels are not controlled. This would mean that it would be difficult to assume that the synchronization occurred to the odour exposure. 

Generalisability: The samples for research into the menstrual cycle tend to be very small

Self-reports – Retrospective data: Most of the research require women to self-report the onset of their cycle. This means we can’t be completely sure whether what is reported is the truth. 

• Discuss the role of exogenous zeitgebers (external) on Infradian rhythms (16). This will involve you creating arguments as to the extent to which EZ’s play a role, or do EP’s play more of a role in influencing Infradian rhythms

Research to support EZ’s: Research suggests that the menstrual cycle is, to some extent, governed by exogenous zeitgebers (external factors). Reinberg (1967) examined a woman who spent three months in a cave with only a small lamp to provide light. Reinberg noted that her menstrual cycle shortened from the usual 28 days to 25.7 days. This result suggests that the lack of light (an exogenous zeitgeber) in the cave affected her menstrual cycle, and therefore this demonstrates the effect of external factors on infradian rhythms.

Research to support EZ’s: There is further evidence to suggest that exogenous zeitgebers can affect infradian rhythms. Russell et al. (1980) found that female menstrual cycles became synchronised with other females through odour exposure. In one study, sweat samples from one group of women were rubbed onto the upper lip of another group. Despite the fact that the two groups were separate, their menstrual cycles synchronised. This suggests that the synchronisation of menstrual cycles can be affected by pheromones, which have an effect on people nearby rather than on the person producing them. These findings indicate that external factors must be taken into consideration when investigating infradian rhythms and that perhaps a more holistic approach should be taken, as opposed to a reductionist approach that considers only endogenous influences.

Research to support EZ’s: Stern & McClintock (1998) took samples of 9 women’s pheromones at different stages in their menstrual cycles by putting pads in their armpits. They were worn for around 8 hours of the day to ensure the pheromones were picked up. The pads were treated with alcohol then frozen, to be rubbed on the upper lip of the other participants. The other participants were 20 women with irregular periods. On day one, pads from the start of the menstrual cycle were applied to all 20 women, on day two they were all given a pad from the second day of the cycle and so on. McClintock found that 68% of the women experienced changes to their cycle which brought them closer to their ‘odour donor’.

Research to support EP’s: There is research to suggest that EP’s play a role in infradian rhythms such as the menstrual cycle. Penton-Volk et al. (1999) found that woman expressed a preference for feminised faces at the least fertile stage of their menstrual cycle, and for a more masculine face at their most fertile point. These findings indicate that women’s sexual behaviour is motivated by their endogenous pacemakers such as the hormones within their cycle. In this case during the ovulation phase women are more focused on masculinity in order to increase the success of conception.  This highlights the importance of studying EP’s in relation to human behaviour, and therefore the role of EZ’s are not able to fully explain behaviour. 

Research to support EZ’s: Finally, evidence supports the role of melatonin in SAD. Terman (1988) found that the rate of SAD is more common in Northern countries where the winter nights are longer. For example, Terman found that SAD affects roughly 10% of people living in New Hampshire (a northern part of the US) and only 2% of residents in southern Florida. These results suggest that SAD is in part affected by light (exogenous zeitgeber) that results in increased levels of melatonin.

• What is the practical application of these findings? Why would would women need to have regular periods? Who might benefit from this knowledge? 
• What’s more influential? Endogenous pacemaker or Exogenous zeitgebers? Are there individual differences at play here? 

Discuss the role of endogenous pacemaker (internal) on Infradian rhythms (16). This will involve you creating arguments as to the extent to which EP’s play a role, or do EZ’s play more of a role in influencing Infradian rhythms. You can use some of the points from the essay above to help you with this. 

Research to support EP’s: There is research to suggest that EP’s play a role in infradian rhythms such as the menstrual cycle. Penton-Volk et al. (1999) found that woman expressed a preference for feminised faces at the least fertile stage of their menstrual cycle, and for a more masculine face at their most fertile point. These findings indicate that women’s sexual behaviour is motivated by their endogenous pacemakers such as the hormones within their cycle. In this case during the ovulation phase women are more focused on masculinity in order to increase the success of conception.  This highlights the importance of studying EP’s in relation to human behaviour. 

Research to support the role EZ’s: There is evidence to suggest that exogenous zeitgebers can affect infradian rhythms. Russell et al. (1980) found that female menstrual cycles became synchronised with other females through odour exposure. In one study, sweat samples from one group of women were rubbed onto the upper lip of another group. Despite the fact that the two groups were separate, their menstrual cycles synchronised. This suggests that the synchronisation of menstrual cycles can be affected by pheromones, which have an effect on people nearby rather than on the person producing them. These findings indicate that external factors must be taken into consideration when investigating infradian rhythms and that perhaps a more holistic approach should be taken, as opposed to a reductionist approach that considers only endogenous influences.

Ultradian Rhythms

Ultradian rhythms last fewer than 24 hours and can be found in the pattern of human sleep. 

This cycle alternates between REM (rapid eye movement) and NREM (non-rapid movement) sleep. The cycle starts at light sleep, progressing to deep sleep and then REM sleep, where brain waves speed up and dreaming occurs. This repeats itself about every 90 minutes throughout the night.

A complete sleep cycle goes through the 3 stages of NREM sleep before entering REM and then repeating. Research using EEG has highlighted distinct brain waves patterns during the different stages of sleep.

1. Stage N1 is the ‘light sleep’ stage. During this stages brainwave patterns become slower and more rhythmic, starting with alpha waves progress to theta waves.

2. Stage N2 is called ‘deeper sleep’. where it is difficult to wake someone up.  Heart rate falls, body temp falls.

3. Stage N3 is called “Slow wave Sleep” Heart rate at it’s lowest with Delta waves being the main level of activity in this stage.

3. Finally the last stage is REM (or dream) sleep. Here is the body is paralyzed (to stop the person acting out their dream) as your brain’s activity is similar to being awake and active.

On average, the entire cycle repeats every 90 minutes and a person can experience up to five full cycles in a night.

But before this happens, the individual needs to fall asleep which is linked to what you have learnt earlier on in this page. Below is a picture which explains in more detail the biological processes involved in keeping you asleep when going through these stages.

https://www.youtube.com/watch?v=Rf9K5izfwJM– Watch this video to get visual and audio description of the different stages.

Evaluation: Ultradian Rhythms

Dement & Kleitman, Shapiro 1981 & Haider 1970- Watch the video above for details of this research. Does this support what you’ve learnt about the different sleep stages (duration and dream activity in REM)?

They tend to measure sleep stages using EEGs. Think back to your lessons on ways of measuring the brain. What are the weakness of this measurement of sleep cycles? How does this affect the conclusions of research into sleep stages and therefore the assumptions we have about sleep stages? If we are using a flawed measurement then how certain can we be of the conclusions drawn?

Tucker et al. (2007) found significant differences between participants in terms of the duration of each stage, particularly stages 3 and 4 (just before REM sleep). This demonstrates that there may be innate individual differences in ultradian rhythms, which means that it is worth focusing on these differences during investigations into sleep cycles. Could also use to question the generalisability of studies of sleep stages?

Randy Gardener remained awake for 264 hours. While he experienced numerous problems such as blurred vision and disorganised speech, he coped rather well with the massive sleep loss. After this experience, Randy slept for just 15 hours and over several nights he recovered only 25% of his lost sleep. Interestingly, he recovered 70% of Stage 4 sleep, 50% of his REM sleep, and very little of the other stages. These results highlight the large degree of flexibility in terms of the different stages within the sleep cycle and the variable nature of this ultradian rhythm.

The growing demands for sleep trackers (fitbits, applewatched etc) means that more and more people are aware of the quality of sleep they are getting. Practical application of this is??? Think back to evaluation of sleep wake cycle!

Research into Caffeine (Drapeau et al, 2006) shows that when exposed to 200mg of caffeine, compared to a placebo, throughout a day there were significant affects on sleep. Compared with the placebo condition, the evening ingestion of caffeine lengthened sleep latency (longer to fall asleep), reduced sleep efficiency (sleep vs time in bed), decreased sleep duration and amount of stage 2 sleep. Caffeine also reduced activity in delta frequencies in frontal, central and parietal brain areas, but not in prefrontal (PF) and occipital regions.

Full Drapeau et al 2006 article here