Biological Rhythms

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  • Circadian
    • Information
      • Repeats every 24 hours
    • Sleep Wake Cycle
      • Depends on physiological and psychological processes
      • Consistent sleep pattern suggests endogenous mechanisms e.g. biological clock
        • This can be overridden by psychological factors e.g. anxiety, or external factors e.g. light/dark cycle
        • Biological clock
          • SCN lies above optic chiasm and is supplied by small braches from 2 optic nerves.
            • protein synthesis occurs in the SCN
              • Protein is produced until it reaches a level which inhibits further growth then protein levels decline until a certain level when it restarts again.
                • This generates a natural endogenous rhythm between 24.5 and 25.5 hours.
          • Pineal gland is linked to SCN by a neural pathway, when stimulated it releases melatonin. Low light = high melatonin
            • Melatonin enhances production of the neurotransmitter serotonin which causes sleep.
          • Research
            • Morgan's hamsters
              • Morgan removed the SCN in hamsters and found that their circadian rhythm disappeared. However, when the SCN was replaced by those of foetal hamsters, the circadian rhythm was re-established. 
                • Unethical to use hamsters as they cannot give fully informed consent to the procedure.
                • Lesions were created in their brain in order to remove the SCN and this would have caused pain and suffering.
                • As non-human animals were used, the results may not be easily generalised to humans and their circadian rhythms.
                • Deterministic - concludes that the sleep wake cycle is determined by the SCN, which is an endogenous pacemaker. The freedom of choice and free will to choose to sleep whenever the hamsters want is not accounted for.
                • Knowing about the role of the SCN can improve understanding of sleep disorders and circadian rhythms, as very little is known. Therefore, the results of the study have real life application. 
            • DeCoursey
              • Removed the SCN in 30 chipmunks and then returned them to their natural habitats. They were observed alongside controls. After 80 days, significantly more of the chipmunks with no SCN had been killed.
                • Chipmunks remained awake in their burrows so weasels could hear them and locate them.
                  • Ethical Issues
                    • Animals are able to feel pain and distress,
                  • Animal Study
                    • Stress in labs affects animals behaviours making results useless.
                    • Cannot extrapolate data - humans have cognitions.
                  • Would not be possible to do on humans.
                    • Animal Study
                      • Stress in labs affects animals behaviours making results useless.
                      • Cannot extrapolate data - humans have cognitions.
            • Ralph et al
              • Used hamsters with a genetic abnormality affecting their circadian cycle. (20 hour cycle rather than 24h)
                • Their brains were removed and placed in the brains of normal hamsters.
                  • Eventually the experimental group also had circadian rhythms of 20 hours.
                    • This shows that SCN controls circadian rhythms.
            • Folkard
              • 12 pps attempted to adapt to 22 hour day.
                • only one did
                  • Body's circadian rhythm can adapt slightly to fluctuations but there are limits.
            • Schochat et al's Sleep gate
              • 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
              • Only a correlation
      • Exogenous Factors
        • Research
          • Miles et al
            • Blind from birth. Had circadian rhythm of 24.9 hours.
              • Exposed to external zeitgebers e.g. clocks.
              • Had to take medication
          • Luce and Segal
          • Siffre's cave study
            • Spent 6 months underground. No clocks, radios or sunlight.
              • Monitored remotely by researchers on the surface.
                • Circadian rhythm changed to between 25-28 hours.
                  • With no external influences the circadian rhythms goes out of sync with typical 24 hour day. So, zeitgebers must play a role.
            • Case Study
              • Difficult to generalise
              • Blind from birth. Had circadian rhythm of 24.9 hours.
                • Exposed to external zeitgebers e.g. clocks.
                • Had to take medication
        • SCN controlled internally or by light
          • Ability to respond to external cues allows animals to adapt to their environment.
            • e.g. animals can adapt to seasonal variations
    • Temperature cycle in humans
      • Information
        • Linked to cognitive performance
        • Lowest 4:30am = 36 degrees
        • Highest 6pm = 38 degrees
        • Trough after lunch
      • Research
        • Folkard
          • Asked to recall a story from a week before.
            • pm group had superior recall
              • Individual groups, am vs pm
              • RWA: Spanish schools send pupils home after lunch in circadian trough. Spain scores higher in education rankings.
          • Individual groups, am vs pm

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