They also had significantly higher levels of circulating fatty acids putting them at greater risk of CHD and hypertension. Fast or slow rotation? Although most research suggests a clockwise rotation is to be preferred, there is disagreement over the speed of rotation. Czeisler main man in this area recommends a slow rotation, for example spending at least three weeks on each shift. Bambra however, prefers a faster rotation of just 3 to 4 days on each pattern so the body never has time to adjust to the new cycle. Fixed shifts tend to be rarer, mostly because of the unsociable hours involved.
For example working a permanent 10pm to 6am shift. Although this allows time for resynchronisation with the worked adjusting to the shift pattern it does create problems at weekends when people revert back to a normal sleep-wake pattern. Using artificial light to reset the body clock Boivin et al put 31 male participants on an inverted sleep pattern so they were awake at night and slept during the day.
This lasted for three days. Each day when they woke they were sat in front of dim lights for 5 hours and then placed in one of four conditions: Very bright light Bright light Ordinary room light Continued dim light Core body temperature was recorded and used as a measure of how well they were adapting to the new rhythm. After three days: Group 1 had advanced by five hours they were adapting to the new pattern best Group 2 had advanced by three hours Group 3 had advanced by one hour Group 4 had drifted backwards by one hour were failing to show any signs of adapting.
Outline the Circadian Rhythm Essay Example
Conclusion Artificial light, even ordinary room light can help us adapt our biological rhythms to suit the environment; however, brighter light is even more effective. Clearly this could be useful in the workplace to help shift workers to adapt to changing sleep-wake cycles. We shall consider the stages of sleep. This whole cycle then repeats itself three or four more times during the night, each cycle lasting about 90 minutes.
There are a number of similar cycles during the daytime too.
Outline and evaluate research into circadian rhythms (8+16 marks)
Sometimes these are referred to as diurnal. Examples include eating approximately every four hours , smoking and urination.
Aserinsky and Kleitman Nine participants were studies seven male and two female Participants ate normally excluding coffee and alcohol then arrived at the laboratory just before their normal bedtime. Participants were woken by a doorbell at various times during the night and asked to describe their dream if they were having one, then returned to sleep. They confirmed whether they were having a dream and described the content into a recorder.
The direction of eye movements was detected using electrodes around the eyes. Participants were woken after the persistence of a single eye-movement pattern for more than one minute and asked to report their dream. The eye-movement patterns were either: mainly vertical, mainly horizontal, both vertical and horizontal, very little or no movement.
Findings : Uninterrupted dream stages lasted minutes mean approx 20 minutes , were typically longer later in the night and showed intermittent bursts of around REMs. The cycle length varied between participants but was consistent within individuals, eg 70 for one, for another. Participants frequently described dreams when woken in REM but rarely did so from NREM sleep although there were some individual differences and this differences was marked at the end of the NREM period within 8 minutes of cessation of REM — only 6 dreams recalled in awakenings.
In NREM awakenings, participants tended to describe feelings but not specific dream content. REM duration and number of words in the narrative were significantly positively correlated.
Outline and evaluate the consequences of disrupting biological rhythms
Eye movement patterns were related to dream content, eg horizontal movements in a dream about throwing tomatoes, vertical ones in a dream about ladders and few movements in dreams about staring fixedly at something. Evaluation As with most sleep research, sample size is very smalln making generalisations difficult, particularly when there are such great individual differences between participants. Sleep laboratories are very artificial settings. However, sleep studies like this do allow for physiological measurements which are objective and replicable.
Unfortunately self-report techniques are just the opposite, subjective and non-verifiable. Given the fragile nature of dreams self report of these must be seen as particularly unreliable. Awake The brain is obviously active and shows what is called beta activity see EEG above.
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When we relax, for example close our eyes or meditate the brain shows alpha activity. Stage 1 sleep 15 minutes This occurs at the start of a nights sleep. It lasts a matter of minutes and you will all be familiar with it since we often wake from this stage. In fact these hallucinations are referred to as hypnogogic phenomena and usually comprise fleeting images rather than the bizarre stories more characteristic of dreaming. The eyes may roll slowly. Stage 2 sleep 20 minutes After about a minute or so we enter stage 2. We are still very easily woken. Stage 3 sleep 15 minutes The brain waves start to slow and become higher in amplitude and wavelength.
These are called delta waves and are associated with deep sleep. We are now more difficult to wake. First time round in the night this stage is brief, only a few minutes, but we spend longer in it later in the night. Stage 4 sleep 30 minutes In many respects this is a continuation of stage 4, however, delta waves now constitute most of the brain activity and we are now at our most relaxed. At this stage we are very difficult to wake up and even vigorous shaking may not be sufficient to wake some people, me included.
However, a quiet but meaningful sound such as a baby crying can be sufficient, again indicating that the brain still retains some degree of awareness to external stimuli! Heart rate and blood pressure fall, muscles are very relaxed and temperature is at its lowest. The brain now becomes very active, almost indistinguishable from a waking brain. Remember the activation-synthesis theory of dreaming? The pons in the midbrain throws out bursts of electrical activity into the cortex lighting it up like a Christmas tree.
Heart rate and blood pressure increase, as does body temperature, and the eyes twitch rapidly giving this stage its name. But, despite this frantic activity the body remains motionless, cut off from the brain by the pons.
REM is now thought by some to be the deepest stage of sleep since it is now that we are most difficult to wake up. However, this could be as a result of being so absorbed in our dreams.
Paralysis appears to be to prevent the body acting out our dreams and endangering our lives. Cats that have had lesions to the pons do in fact appear to act out their dreams. Remember, however, that we have no certain way of knowing whether lower species do dream; it is merely assumed that they do because all warm blooded creatures birds and mammals , with the exception of the very early egg-laying mammals, have REM sleep. Our first visit to REM typically lasts about for about 10 minutes and we start our journey back down to stage 2, stage 3 and stage 4 sleep. This cycle repeats throughout the night, however, as the diagram below illustrates, we spend most of the first half of the night in deep sleep slow wave or NREM , and most of the second half in REM sleep.
This last cycle contains no stage 3 or stage 4 sleep so under normal conditions we will emerge from either REM or stage 2 and the waking process may be accompanied by further hypnogogic images as was mentioned in stage 1. Strictly speaking on waking these are referred to as hypnopompic. Obviously there are large individual differences between people. Some may sleep much shorter periods, others who have been sleep deprived will spend longer in stage 4 and REM, and the pattern changes with age.
In humans the best examples are menstrual cycle and PMS Pre-Menstrual Syndrome which occurs a few days prior to the onset of bleeding and is characterised information for the boys , by loss of appetite, stress, irritability and poor concentration. There are a number of rhythms that are cyclic over about one year.
A human example would be SAD Seasonal Affective Disorder , more on this later; and in the animal world migration, mating patterns and hibernation of some species. Although it is apparently normal for most people to feel more cheerful in the summer months than in winter, a small number of people suffer an extreme form of this that appears to be related to the lack of bright light in the winter months. Additionally as you will hopefully recall from your work on depression, serotonin is implicated in mood.
See how eventually all these strands knit together! At night low light levels stimulate the production of melatonin, this is what triggers sleepiness. Therefore you would expect the lower light levels of the winter months to have a similar affect. In areas where light levels are exceptionally low for prolonged periods, such as the Polar regions, you would expect the effects to be particularly noticeable.
Research evidence The symptoms of SAD can be reduced in polar regions by sitting patients in front of very bright artificial lights for at least one hour per day. This lowers the levels of melatonin in the bloodstream which in turn reduces the feelings of depression. The precise mechanism for this is still unclear. It could be that melatonin released from the pineal gland has a direct affect on mood or it could have its influence indirectly through serotonin.
Drugs used to treat depression such as Prozac and other MAOIs monoamine oxidase inhibitors , appear to work by altering serotonin levels. Terman et al researched participants with SAD.
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Another 39 were exposed to negative ions a placebo group. The researchers conclude that bright light administered in this way may be acting as a zeitgeber and resetting the body clock in the morning. Research into SAD has led to effective treatments suggesting that the theory has some validity. However, there does also appear to be a genetic component. Note: SAD varies over a yearly cycle so can be viewed as an infradian or circannual cycle. SAD can be discussed in an essay on disruption of biological rhythms.