Biological rhythms

Key Concepts 1 Biological rhythms: regular variations in the biological activity of living organisms, such as sleep, body temperature, alertness, neurotransmitter levels, etc. Circadian rhythms: 24 hrs periodicity Infradian rhythms: less than once in 24 hrs Ultradian rhythms: more than once in 24 hrs

Key concepts 2 Endogenous pacemakers: Biological ‘clocks’ in the brain controlling biological rhythms. In the case of sleep, the suprachiasmatic nucleus in the hypothalamus Exogenous Zeitgebers (Timegivers): External stimuli that help towards regulating biological rhythms to the outside world. In the case of sleep, sunlight is key one (but not alone; others?)

Circadian rhythms 1 Etymology: circa (almost), dies (day) Examples: sleep/waking, body temperature Circadian rhythms are needed to balancing behaviour and body states to environmental changes

Circadian rhythms 2 Folkard et al., (1985) argues that bodily rhythms (during circadian time) are primarily an endogenous property, which does not depend on exogenous cues. Example comes from the sleep and waking cycle. Some people may have only 45 minutes of sleep each night, 5 to 6 hrs or more

Circadian rhythms 3 The symptoms of many illnesses fluctuate over the 24hr cycle, such as hay fever, and are worst around dawn; heart attacks are likely to happen in the morning when blood is more prone to clotting (thickened blood) Chronotherapeutics (Dobson, 1999): Description of drug effectiveness during night when blood is thinner in density (compactness) Hormones such a prolactin (producing milk in women) also vary over the day

Infradian rhythms 1 Occurring to a period more than 24 hrs, such as the human menstrual cycle Some of them may take place on a yearly basis and they are known as circannual rhythms, such as the migration of birds, and hibernation in squirrels bears, and hedgehogs

Infradian rhythms 2 Menstruation (likely to happen every 28 days). In a matter of months it gets established in the woman’s cycle. Menstruation is also influenced by environmental events. The synchronisation of menstrual periods attributes to the hypothesis of the unconscious detection of chemical scents called pheromones (relating to the physiology or the attraction of other species of the same or different sex) secreted at certain times during the menstrual cycle (Sabbagh & Barnard, 1984; Russell et al., 1980)

Infradian rhythms 3 The Pre-Menstrual Syndrome (PMS): The variety of behavioural and emotional effects taking place at several phases of the menstrual cycle (5 days before the onset of menstruation) Large proportion of accidents and a decline in the quality of schoolwork were reported during the pre-menstrual interval (Dalton, 1964; Hardie, 1997)

Infradian rhythms 4 The pituitary gland governs the phases of the menstrual cycle by influencing changes in the endometrium (the walls of the uterus) and the preparation of the ovum Timonen et al., (1964) showed that during lighter months conceptions increased, whereas not during darker months

Infradian rythms 5 Menstruation in the absence of Zeitgebers: It has been observed that menstruation starts mainly in winter (for the first time), and that because the pineal gland is affected by the melatonin’s secretion and the reproduction system in general (conceptions in lighter months) (Reinberg, 1967)

Infradian rhythms 6 Seasonal affective disorder (SAD): Seasonal changes in behaviour can also be found in human beings. Individuals feel depressed during winter, and elated during summer. One suggestion is that absence of light increases melatonin, and what is suggested is light therapy (Rosenzweig et al., 1999). As an example, depression is mostly seen in northern than southern countries instead

Ultradian rhythms 1 Shorter than 24 hrs, such as smoking, eating and drinking, renal excretion (discharging waste through kidneys), sleep (different stages studied through EEG-Electro-Encephalography), etc. (Loomis et al., 1937)

Ultradian rhythms 2 (Recording Sleep) EEG (Electro-EncephaloGraphy): It measures and records the electrical activity in a person’s brain EOG (ElectrOculoGram) it records eye movements during sleep EMG (ElectroMyoGram) it records muscle activity during sleep

Endogenous pacemakers and exogenous zeitgebers Endogenous pacemakers represent an inherited genetic mechanism towards rest, such as the ‘sleepy behaviour’ of an unborn baby that has never been exposed to the outside world (Pineal gland/Suprachiasmatic nucleus) Exogenous zeitgebers refer to a behaviour fully controlled by the external world, such as the effect of light

The role of the pineal gland and the suprachiasmatic nucleus (SCN) Pineal gland: It contains light receptors that correspond to external light. Neurons in the pineal gland convert the neurotransmitter serotonin to melatonin, so sleep and waking cycles to be synchronised Suprachiasmatic nucleus (SCN): It regulates the amount of melatonin in the pineal gland and it is also connected to the retina of the eye, controlling the light coming in. Light and melatonin are linked through the SCN

SCN SCN have a nerve input directly from the retina of the eye, so they are kept informed about the zeitgebers of light and darkness. In darkness this information is transmitted to the pineal gland which manufactures melatonin a hormone which stimulates the production of serotonin in the raphe nucleus this hormone causes reduced levels of arousal and so induces sleep. When Light enters through the eyes it stimulates the SCN to produce an inhibiting factor (probably a protein) This inhibits the production of melatonin by the pineal gland and so maintains arousal levels – keeping you alert and awake!

The Sleep-Wake Cycle Sleepiness Supra-Chiasmatic Nucleus (SCN) Pineal Gland Melatonin Sleepiness

L.O: Be able to outline and evaluate research relevant to the affects of endogenous pacemakers and exogenous zeitgebers on Circadian rhythms

Research Evidence SUPPORTING Endogenous Control. Siffre (1975) Cave study (see book, p 8) Morgan’s Hamster studies (1995) – When SCN was removed from hamsters their circadian rhythms disappeared. Transplanting with SCN cells re- established the rhythms = SCN is main pacemaker. Shochat et al’s “Sleep gate” study (1997) found a close relationship between sleep propensity and melatonin. Six participants spent 29 hours in a sleep laboratory where for 7 minutes in every 20 they had to try to sleep. The highest sleep propensity, the “sleep gate” was found to occur in late evening and the highest levels of melatonin preceded this by 100-120 minutes. This supports the role of melatonin in sleep propensity.

What AQA has to say about Siffre!

Research evidence SUPPORTING exogenous influence via Zeitgebers Miles et al’s (1977) study of a blind man. The man blind from birth had a circadian rhythm of 24.9 hours. He had to use stimulants and sedatives to adjust his sleep-waking cycle to the standard 24 hours. This shows that light is the main exogenous factor in the ‘24 hour cycle’, as it reduces the “natural” 25 hour rhythm (of the blind man at least) to 24 hours. Luce and Segal (1966) Artic Circle study People who live within the Artic circle sleep for 7 hours per night despite the fact that during the summer the sun never sets. This shows that light is not the only zeitgeber, nor is the biological clock only influenced by light. Other exogenous factors such as social customs and psychological factors such as motivation, are important. CULTURE as zeitgeber!

Research to biological rhythms (Evaluation) Research findings: Endogenous pacemakers and exogenous zeitgebers play an important role in regulating the human behaviour Generalizability of research: Endogenous mechanisms can control sleep/waking in the absence of light/Exogenous zeitgebers; we use light to ‘synch’ the clock of our biological rhythms with the planet!

Research to biological rhythms (Evaluation) Individual differences: Biological rhythms do not operate the same in all people, or in subjects of different parts of the world Number of participants: Where the research was carried out with single participants (or a handful), the findings ought only be generalised with care

Summary Biological rhythms play an important role in our sleep and wake cycle, as well as our cognitive and emotional preoccupations Pineal gland, and suprachiasmatic nucleus relate endogenous pacemakers to exogenous zeitgebers

There are three main types of bodily rhythm There are three main types of bodily rhythm. The first is the ___________ bodily rhythm, which has a cycle of less than a day. Two examples of this are ___________ and ___________. Cycles that are approximately a day in length are known as ___________ rhythms. Even when external cues are removed, there is evidence for a _______-___________ cycle, as shown by studies where light is removed. However, this can be shorter or longer than 24 hours, depending on the _______ of animal it is. This is evidence for an internal “clock”, known as an ____________. The final type of bodily rhythm is one that lasts for longer than a day, and this is known as an ____________ rhythm. An example of this are the ____________.

A lot of research has suggested that seasons of the year can affect this, as in the case of ________, a condition where lack of light can lead to depression. The light affects the ___________ (part of the brain). There seems to be a common trend in bodily rhythms amongst individuals, but also slight _______________ There is evidence to suggest that bodily rhythms are independent of each other - __________ et al (1981) found that when ________ monkeys had damage to their sleep-wake cycle, their temperature cycles were not affected. However, we need to do more research into humans, as we cannot ____________ from animal findings to humans.

A circadian rhythm is a variation in biological activity which occurs once every 24 hours. One example is the sleep/waking cycle, which occurs once very day. It is influence by exogenous zeitgebers such as light, temperature or noise. Exogenous zeitgebers are environmental factors which have an effect on our endogenous pacemakers (the internal biological clock. These work together to provide us with a sleep/wake cycle which is within 24 hours and they show the nature and nurture side of the sleep/wake cycle.

Extension Questions In 100 words outline what we mean by ‘endogenous pacemaker’ What is the name given to external events that play a role in rhythmic activities? Give an example Discuss the association between SAD and exogenous zeitgebers? Evaluate the research in biological rhythms

Question Answer 1) Outline what we mean by an endogenous pacemaker 2) What is the name given to external events that play a role in rhythmic activities? Give an example 3) Name four types of biological rhythm, describe each one briefly, and give an example of each 4) Prepare an outline (in 100 words) of seasonal affective disorder and its relevance to biorhythms 5) Name and describe two brain structures with important roles as biological clocks 6) What hormone is involved in regulating our biological rhythms? Where is it released from? 7) Write a 100-word summary of the findings of 2 studies of free-running biological rhythms and what they can tell us about the control of biological rhythms 8) Identify and give a brief account of two critical (AO2) points relating to studies of free-running biological rhythms 9) Outline in 100 words two examples of the disruption of biological rhythms in everyday life and their effects on behaviour