Individual differences To know how individual differences influence Circadian research To understand the role of genes in circadian phase disorders To be able to explain and justify animal research for RWA

Key concepts Individual differences (variation between individuals) – Onset differences – Length differences Circadian phase disorders – FASPS – DSPS Personality difference (Siffre) There are huge variations in Circadian rhythm lengths and onset making it difficult to generalise

The Biological Clock - How does it work? Thought mainly to be an endogenous (internal) mechanism Our internal rhythms are thought to be generated by protein synthesis within the SCN. Protein is produced for a period of hours until it reaches a level that inhibits further production. Over the next few hours the protein level gradually falls, when it drops to a certain ‘threshold’ level then production of the protein re-starts. This generates an internal (endogenous) biological rhythm – in humans of between 24 ½ and 25 hours. This is what happens inside the SCN Protein synthesis takes place over a 24 hour period

THE TICKING OF THE BIOLOGICAL CLOCK Suprachiasmatic Nucleus (SCN) The basis of the circadian rhythm lies in interactions between certain proteins, creating the ‘tick’ of the biological clock; it is an ingenious negative feedback loop. Darlington et al. (1998) first identified such proteins in the fruit fly, drospholia. In the morning, two proteins, CLOCK and CYCLE (CLK-CYC) bind together. Once joined, CLK-CYC produce two other proteins, PERIOD and TIME (PER-TIM). PER- TIM has the effect of rendering the CLK-CYC proteins inactive, so that, as PER- TIM increases, CLK-CYC decreases and therefore PER-TIM starts to decrease too (negative feedback). This loop takes about 24 hours and, hey presto, you have the biological clock! The actual proteins vary from animal to animal. In humans the main pairs are CLOCK-BMAL1 and PER-CRY (BMAL1 and CRY are also proteins). This protein mechanism is present in the SCN (the central oscillator), and is also present in cells throughout the body (peripheral oscillators). The presence of peripheral oscillators explains why there are different rhythms for different functions such as hormone secretion, urine production, blood circulation and so on.

THE TICKING OF THE BIOLOGICAL CLOCK Suprachiasmatic Nucleus (SCN) The basis of the circadian rhythm lies in interactions between certain proteins, creating the ‘tick’ of the biological clock; it is an ingenious negative feedback loop. In humans the main pairs are CLOCK-BLMAL1 and PER-CRY (BMAL1 and CRY are also proteins). This protein mechanism is present in the SCN (the central oscillator), and is also present in cells throughout the body (peripheral oscillators). The presence of peripheral oscillators explains why there are different rhythms for different functions such as hormone secretion, urine production, blood circulation and so on.

Genes Any mutation with the genes affect the protein, which in turn can cause a mutated circadian S/W cycle

Individual differences There are two important types of individual difference. One is the cycle length; research has found that circadian cycles in different people can vary from 13 to 65 hours (Czeisler et al., 1999). The other type of individual difference relates to cycle onset – individuals appear to be innately different in terms of when their circadian rhythms reach their peak. – For example, Duffy et al. (2000) found that morning people prefer to rise early (Larks)and go to bed early about 6.00 am and pm, whereas evening people prefer to wake and go to bed later, (Owls) am and 1.00 am respectively.

Onset Differences: FASPS and DSPS Clock genes normally keep us awake during the day and asleep at night. But when a clock gene mutates, it can disrupt the normal sleep wake cycle. A mutant hPer2 gene is responsible for an inherited sleep pattern known as "familial advanced sleep phase syndrome" (FASPS). People with FASPs are "morning larks" who usually get sleepy by 7 p.m. and wake up around 2 a.m. Another sleep condition, called "delayed sleep phase syndrome," has the opposite effect, turning people who have it into extreme night owls. They fall asleep very late and have trouble waking up in the morning. Delayed sleep phase syndrome has been linked to the hPer3 gene. Worksheet Phase Advance Phase Delay Old People Teenagers

Protein synthesis in the SCN: Negative feedback loop CLK PER + CRY BLMAL1 When PER and CRY bind they render CLK and BLMAL1 inactive 24 hour Circadian cycle 20, 000 cells in the SCN Clock and BLMAL1 bind together to produce...

FASPS and DSPS Clock genes normally keep us awake during the day and asleep at night. But when a clock gene mutates, it can disrupt the normal sleep cycle. A mutant hPer2 gene is responsible for an inherited sleep pattern known as "familial advanced sleep phase syndrome" (FASPS). People with FASPs are "morning larks" who usually get sleepy by 7 p.m. and wake up around 2 a.m. Another sleep condition, called "delayed sleep phase syndrome," has the opposite effect, turning people who have it into extreme night owls. They fall asleep very late and have trouble waking up in the morning. Delayed sleep phase syndrome has been linked to the hPer3 gene. Worksheet Phase Advance Phase Delay Old PeopleTeenagers

Protein synthesis in the SCN: Negative feedback loop CLK PER + CRY BLMAL1 When PER and CRY bind they render CLK and BLMAL1 inactive 24 hour Circadian cycle 20, 000 cells in the SCN Clock and BLMAL1 bind together to produce...

These studies are typical of the biological approach to understanding behaviour: they propose that human behaviour can be explained in terms of structures in the brain and in terms of hormonal activity. However, human behaviour is often more complex than this because people can override biologically determined behaviours by making choices about what they do. On the other hand, sometimes it may not be possible to override biological factors and biological rhythms may be a case in point. A powerful example of this was the study of a man who was blind from birth and had a circadian rhythm of 24.9 hours. He was exposed to various exogenous zeitgebers such as clocks and social cues, yet had great difficulty in reducing his internal pace. This made it very difficult for him to function and, as a result, he had to take stimulants in the mornings and sedatives at night in order to get his biological rhythm in time with the rest of the world (Miles et al, 1977).

The circadian variation in core body temperature has been linked to cognitive abilities. Folkhard et al (1977) looked at the learning ability of 12 – 13-year old children who had stories read to them at either 9.00 am or 3.00 pm. After one week, the afternoon group (higher core body temperature) showed both superior recall and comprehension. This suggests that our long- term recall is best when body temperature is highest. There is evidence that temperature changes do actually cause the changes in cognitive performance. Giesbrecht et al (1993) lowered body temperature (by placing pp’s in cold water) and found that cognitive performance was worse on some tasks.

Justification of animal research: Working when we should be sleeping! Human error and shift work Negative effects of sleep deprivation – e.g. decreased attention – slowing of reasoning skills – impaired reaction could have serious consequences on the ability to do work or drive safely. Possible justification for animal research Practical application of Psychology in the real world

Describe the biological clock that controls the human circadian sleep/wake cycle (6m ) Success criteria: – SCN – Innate – Biological mechanism – Protein synthesis – Controlled by genes – Clock-BlMal1=Per+Cry... – Negative feedback loop – Giving a 24 sleep wake cycle