Biological rhythms: Infradian and Ultradian

• What are infradian rhythms?

  Biological rhythms lasting longer than 24 hours
• What causes Seasonal Affective Disorder (SAD)?

  Less serotonin and more melatonin in winter
• What are key exogenous factors affecting SAD?

  Environmental light levels during winter months
• How does decreased light affect melatonin levels in SAD?

  Melatonin levels are secreted for longer periods
• What are key exogenous factors affecting the menstrual cycle?

  Weight, stress, diet, and pheromones
• Who conducted the study on menstrual cycles and pheromones?

  McClintock
• What are ultradian rhythms?

  Biological patterns occurring within 24 hours
• What key factors affect sleep and BRAC cycles?

  Caffeine and alcohol
• How often does the sleep cycle occur?

  Approximately every 90 minutes
• How many main stages are in the sleep cycle?

  Five main stages
• What occurs during light sleep?

  Alpha waves and muscle twitches
• What happens in the second stage of light sleep?

  Theta waves, slowed breathing, and decreased body temp
• What characterizes deep sleep?

  Delta waves and very limited muscle activity
• What occurs during REM sleep?

  Dreaming and beta waves generated
• How does Kleitman relate the BRAC cycle to alertness?

  90-minute cycle of alertness until tired
• What are the stages of the sleep cycle?

  1. Light sleep (Stages 1-2)

  • Alpha waves (Stage 1)
  • Theta waves (Stage 2)

  1. Deep sleep (Stages 3-4)

  • Delta waves

  1. REM sleep (Stage 5)

  • Dreaming and beta waves
• What are the characteristics of BRAC cycles?

  • 90-minute cycles of alertness
  • Feelings of tiredness and hunger
  • Loss of concentration over time
• The study of the effect of pheronomes on the menstrual cycle was measured by McClintock: 29 women with history of irregular periods, took sweat samples (treated cotton pads with alcohol and froze them), rubbed under the noses of the women.
• Strength of infradian rhythms - treatment for SAD

  + Phototherapy found to be effective treatment for depressive tendency due to lack of sunlight.

  + Eastman: 96 ppts to three different conditions - bright light in the morning, in the evening, or morning placebo of normal light.

  + Near complete remission of symptoms with morning phototherapy, however there was recovery in placebo group.

  -Origin of SAD is psychologiocal rather than environmental.
• Strength of infradian rhythms - menstrual cycle synchs?

  + The menstrual cycle is primarily controlled by endocrine system (hormones) but can be affected by exogenous cues

  + Female menstrual cycles synchronise when living together - study similar to McClintock showed that menstrual cycles synchronised even when not in the same vicinity.

  + Evidence for the role of exogenous cues (pheromones).
• Strength of ultradian rhythms - support for sleep stages

  + Dement and Kleitman - distinction between REM sleep and other stages using EEGs to measure brain activity.

  + Controlled for caffeine and alcohol. Significant relationship between REM and dreaming (more active EEG waves).

  + waking up during REM sleep showed consistently clearer dream recall.
• Limitation of ultradian rhythms - individual differences

  -Tucker suggests sleep can be biologically determined through genetics.

  -PPTs studied over 11 days - assessed on sleep duration, time taken to fall asleep and time spent in each stage.

  -Despite consistant environment, deep sleep was the most variable - innate factors = idiographic approach needed.