biorhythms

Biorhythms are distinct patterns of changes in body activity that conform to cyclical time periods. They can be influenced by internal body clocks (endogenous pacemakers) or external changes to the environment (exogenous zeitgebers).

Biorhythms are often synchronised in daily, monthly or annual cycles and are classified as ultradian, circadian and infradian.

Endogenous pacemakers — internal body clocks, affected by environment but can function without. For example, the SCN which receives sensory information from eyes to regulate melatonin production.

Exogenous zeitgebers — cues from environment that regulate time in humans, synchronise EP. For example, light affects the SCN.

Studies on EZ:

• Campbell and Murphy

  • Light shone onto the back of 15 participants knees while they were sleeping, lead to a 3 hour deviation in sleep/wake cycle

  • Suggests skin receptor sites can detect light even when eyes don’t receive it

• Social cues

  • Sleep/wake cycles are random in early infancy but learned at 16 weeks due to parents schedules

  • Adapting to local times can conquer jet lag

• Folkard

  • 12 volunteers, 3 weeks in isolation with no natural light

  • Instructed to go to bed when clock said 23.45 and set alarm for 7.45

  • Clock was sped up after a few days, so 24 hours went in 22 hours instead

  • Only 1 kept pace with 24 hour cycles, the rest followed the clock

    • Suggests internal factors can be overridden by EZ

  • Evaluation: sample size is small, individual differences

• Miles et al

  • Case study of blind man who had 25 hour circadian rhythm

  • Exposed to EZ (e.g daytime noise, alarms) but could not change internal pace

  • Only way to synchronise it was with sedatives and stimulants, suggests light is vital for 24 hour cycle as it was the only EZ he wasn’t exposed to

  • Evaluation: not generalisable, individual differences

Types of biorhythms:

• Circadian — 24 hour cycle

  • Body temp (drops at night), sleep/wake cycle

• Infradian — more than 24 hours for 1 cycle

  • Menstrual cycle, hibernation, seasonal depression

• Ultradian — less than 24 hours for 1 cycle

  • Stages of sleep cycle (90 mins)

circadian rhythm

• Affects eating, sleeping, mating, hormone secretion

• Regulated by internal system (hormones, metabolic rate, temperature) but also external factors like reading the time and when we eat

Suprachiasmatic nucleus in the hypothalamus receives information about light levels from the occipital lobe and alerts pineal gland to produce melatonin.

Melatonin is a sleep-inducing hormone that is inhibited by light (cause of SAD), it is elevated in blood for 12 hours and lowers by 9am.

• Research on SCN:

  • Decoursy — destroyed SCN connections of 30 chipmunks, released into the wild and observed for 80 days. Sleep/wake cycle disappeared, many were killed by predators

  • Ralph — mutant hamsters with 20 hour sleep cycle. Healthy hamsters adopted the same cycle when SCN put into them

  • Morgan — SCN removed from hamsters, sporadic sleep. When cells were re-implanted, effects were reversed

  • Evaluations: evolutionary discontinuity, lowers applicability

Michael Siffre — self-styled caveman that spent time underground to study the effect on his biorhythms

• Deprived of exposure to light and natural sound but had food and water

• 1962: southern Alps, 2 months in a cave, emerged in mid-sept but thought it was mid-aug

• 1972: Texan cave, free-running biorhythm settled to 25 hours and he fell asleep and woke up at regular times

• Small sample size so not generalisable, but repeated twice so it is reproducible

Aschoff and weber — studied students living a bunker that had only electrical light and no windows

• Bodies settled to 25-27 hour sleep/wake cycles

• Suggested that EZ (e.g light) can train EP, light shortens natural circadian cycle to 24

• Their cycles did not stray far from usual so research doesn’t contradict the role of internal factors

• Evaluation: control over extraneous variables increased internal validity, effects of light and clocks were ruled out so causal relationship was established

infradian rhythm

Menstrual cycle — hormone changes to regulate ovulation, can be affected by EZ (like the cycles of other women).

Studies:

• Mcclintock, odour donour

  • 29 women with irregular periods

  • Cotton pads under armpits for 8 hours which was frozen and rubbed on lips

  • 68% had changes to cycle.

• Russell

  • 16 volunteers came in 3 times a week to have liquid applied to upper lip

  • Control group had pure alcohol, experimental group had alcohol and female underarm scent

  • 4/5 in experimental group were synchronised within 24 hours

  • Suggests others’ pheromones act as EZ which can influence EP

  • Evaluation: small sample but had a control group

• Reinberg

  • Woman spent 3 months in a cave with light from a small lamp

  • 25 hour long circadian rhythm and 25 day menstrual cycle

  • Suggests light levels could have an effect on menstrual cycle as an EZ

  • Her body took over a year to readjust menstrual cycle

  • Evaluation: correlational study, extraneous variables controlled but can’t say it was lack of light for certain (could have been differences in food or abnormal lifestyle). It suggests there is an evolutionary advantage of syncing (leads to synced pregnancies so childcare can be shared)

SAD — depressive disorder with seasonal onset, due to lack of light during winter causing melatonin production during the day

ultradian rhythm

Sleep cycle — 90 minutes with distinct stages, recorded using EEG:

• Stage 1: 5-15 minutes, light sleep that can be easily awoken, fairly high brain activity, relaxing and slowing down, alpha waves

• Stage 2: 5-15 minutes, deeper into sleep, sleep spindles on EEG, theta waves

• Stage 3: 20-40 minutes, deeper into sleep, turning into delta waves, body relaxes until its hard to wake

• Stage 4: 40 minutes, deep sleep that is hardest to wake and least active, delta waves, low metabolic rate and release of growth hormones

• REM sleep: initally 15 minutes but lengthens throughout the night, highest brain activity (same as when awake), beta waves, relation, irregular breathing, dreams

Sleep is needed due to energy consumption, so it affected by homeostasis.

Dement and Kleitman:

• Aim — investigate changes in brain activity during sleep using EEG

• Procedure — 7 males, 2 females connected to EEG while sleeping, asked not to drink coffee

• Results — all had REM, high dream recollection if woken during REM but not other stages, rapid eye movements

• Conclusions — sleep has a regular pattern with different waves during each stage

• Evaluations — assumption that REM equals dream is not true because dreams were occasionally recorded in other stages so conclusions may be invalid, EEG is scientific and objective so results are valid and reliable, small sample size, data collection could have confounded results as sleeping in lab could cause atypical reactions so it lacks ecological validity and applicablility

Gagswich:

• 15,500 teenagers at Columbia, 1/5 had depression

• 20% had bedtimes after midnight, 48% regularly got less than 5 hours sleep

• Those who reported getting enough sleep were less likely to be depressed

• Suggests that sleep contributes to mental health

• Evaluation: correlational study, difficult to determine is sleep is the cause (could even be the result), patients could have insomnia or other conditions, internal validity was low

Wakeathons:

• Peter tripp — 201 hours

  • 3 days in, he was abusive and unable to perform cognitive tasks

  • 100 hours in, he was having psychosis and slurred speech

• Randy Gardener — 264 hours

  • 4 days in, he was irritable and had low concentration/memory

  • 9 days in, he struggled to think and speech and was delusional

  • He recovered after 14 hours of sleep

Other sleep studies:

• Shift work — causes desynchronisation

  • Bolvin et al: night workers had reduced concentration at 6am and were more likely to make mistakes

  • Knutsson: there is a relationship between shift work and poor health

• Duffy et al — morning people (wake at 6am, sleep at 10pm) and night people (wake at 10am, sleep at 1am). There are innate differences in circadian rhythms that need to be considered in research