Biological Rhythms - Circadian and Ultradian Rhyth
- Once every 24 hours
- SCN = internal body clock
- Increased light = increased melatonin
- Siffre - 61 days in cave. Sleep/wake cycle = 25hrs, but reached 48 hrs at one point
- Folkard et al - 12 RP's in isolation. Clock was secretly changed. Only one person's rhythm adapted.
- Aschoff and Wever - WWII bunker. RP's had 25 hour cycle. 24 hour cycle when returned to normal.
- More than once every 24 hours.
- 5 stages of sleep (NREM, SWS, REM)
- 90 minute cycle, 5- times per night.
- Friedman and Fisher - BRAC - Eating and drinking cycle. Study of psychiatric patients.
- Dement and Kleitman - REM studies are restricted. Assumption of dreaming sleep. Dreaming can happen in NREM, and not always in REM.
1 of 5
Biological Rhythms - Infradian Rhythms
- Less than once every 24 hours.
- e.g. Menstrual cycle/male monthly cycle
- MENSTRUAL CYCLE: Pituitary glands release hormones which stimulate overy to ripen egg. Progestorone is released which causes increased blood flow. If no pregnancy, lining of womb is shed.
- MALE MONTHLY CYCLE: Empson - 21 RP's. study over 49-102 days. Body temp and alertness varied over 20 days.
- Russell et al - Sweat rubbed onto upper lip of another person. Menstrual cycles synchronised.
- Dalton - Premenstrual Syndrome (physiological problem, psychological symptoms) associated with crime, suicide, accidents. Can be defence in court.
- Seasonal Affective Disorder - Depression in winter. Melatonin and Serotonin released when dark.
2 of 5
Endogenous Pacemakers and Exogenous Zeitgebers
- Hypothalamus received information about light, even when eyes are closed.
- This synchronises the SCN, and sends signal to pineal gland to increase melatonin at night.
- Morgan - Mutant hamsters with sleep cycles of 20hrs. SCn transplanted into normal hamsters - They showed mutant rhythms.
- Folkard - Kate Aldcroft spent 25 days in a cave - sleep cycle was 30hrs. Temperature cycle was 24hrs. Therefore, desynchronsation has occured.
- Entrainment - resetting the SCN with Exogenous Zeitgebers, e.g. light, temp., social cues.
- DeCoursy et al - Destroyed SCN in chipmunks. They were more active at night, and were more likely to be killed.
- Campbell and Murphy - Shone bright lights onto back of RP's knees. Circadian rhythms shifted, therefore artificial light does have an effect.
3 of 5
Disruption of biological rhythms - Shift Work
- Decreased alertness - 00:00-04:00 = low cortisol levels and low body temp. This is a circadian trough.
- Sleep Deprivation - caused by distractions, light, noise, daytime sleep shorter than night.
- Effects on health - Knutson et al - shift work for more thatn 15 years = heart disease risk.
- Solomon - Social disruption caused by shift work. Divorce rates are as high as 60%.
- Gold et al - Rotating shifts are worse - constant changes and disruption cause stress.
- Bambra et al - Forward-rotating shifts are less damaging.
4 of 5
Disruption of biological rhythms - Jet Lag
- Symptoms - Loss of apetite, insomnia, depression, fatigue, nausea, disorientation.
- Winter et al - SCN =1 day to adapt for every 1 hour of time change.
- Recht et al - Baseball teams from west and east America. -East to west = Phase delay (won 44%). West to east = Phase advance (won 37%).
- Other factors - Bad sleep before travelling, travelling is tiring, noise, low-oxygen, noisy passengers
- Boivin et al - 31 men, 4 groups. Sleep cycle inverted for 3 days. When awake, exposed to dim lighting and then either:
- Group 1 - Very bright light. (Advanced 5hrs earlier)
- Group 2 - Bright light. (Advanced 3hrs earlier)
- Group 3 - Normal light. (Advanced 1hr earlier)
- Group 4 - Dim light. (Advanced 1hr later)
- Core body temp. was measured.
5 of 5