Biological rhythms

Biological rhythms

1. Circadian rhythms

   • ~ 24 hours
   • Sleep-wake cycle
     • External cues i.e darkness, time
       • Folkard et al - 'day' shortened to 22 hours, endogenous factors took over showing control
     • endogenous factors control cycle in absence of cues
       • Suprachiasmatic nucleus - main bodily clock
         • Pineal gland responsive to light cues. Serotonin -> melatonin
           • Melatonin controls sleep wake cycle
         • Stephan & Zucker - rat SCN distruction disrupted circadian rhythms inc SWC
           • Rosenwasser et al - animals fed regularly became active before eating, continued after SCN destruction
     • Fulton & Bailey - tumours affecting the SCN caused disrupted SWC
     • Siffre - spent long periods of time in caves. Found SWC stayed around 24 hours
     • Czeisler et al - individual differences 13-65 hours
   • Cortisol - high levels provide alertness - lowest at 12am, highest at 6am. Explains difficulty in waking up early
   • Biologically determinist
     • Some flexibility, go to bed early and wake up at normal time
     • Folkard et al - individual able to maintain 22 hour cycle. Overriding internal clock

2. Infradian & ultradian rhythms

   • Ultradian rhythms < 24 hours
     • Sleep stages
       • Stages 1&2 - relaxed, alpha & theta waves, decreased heart rate & temperature
       • Stages 3&4 - SWS delta waves, decreased metabolism, growth hormone secreted
       • REM - dream time, brain activity similar to consciousness, but body paralysed. Paradoxical state
       • ~ 90 minutes. More REM later in night
       • Dement & Kleitman - woken in REM normally dreaming, however not exclusive
     • Rest-activity cycle - 90 minute cycle
       • Freidman & Fisher - 90 minute pattern between eating & drinking in psychiatric patients
       • Maintains metabolic processes
   • Infradian rhythms > 24 hours
     • The menstrual cycle is an example
       • Russell et al - pheromones can sync menstrual cycles, collecting sweat from one woman and rubbing on the upper lips of other women
         • Can be controlled by exogenous factors
       • PMS can be an effect
         • Dalton - PMS lead to decreased academic achievement, suicide & crime
         • Schonberg et al - women administered higher shocks to a learner a week before menstruation
         • Nicholson - only 5% women suffer PMS
         • Janiger - PMS found in all cultures
     • Seasonal affective disorder (SAD)
       • Melatonin & Serotonin levels possible cause. More darkness - more melatonin, causing less serotonin. Low serotonin associated with depression
         • SAD & PMS inevitable behaviours.
           • Johnson - Woman acquitted of murder due to severe PMS
           • Born et al - Able to will your body into change. People told to wake up earlier had higher ACTH (stress hormone) levels
       • Not an infradian rhythm, just disrupted circadian rhythm from sleeping earlier
       • Phototherapy - treatment using very strong light
         • Eastman et al - 32% increased from placebo effect

3. Endogenous pacemakers & exogenous zeitgebers

   • Endogenous pacemakers
     • SCN nerve cells in hypothalamus
       • Gets light information as it is just above the optic chiasma. Info still received when eyes shut
     • Morgan - hamsters bred with 20 hour circadian rhythm. SCN removed and transplanted. 20 hour cycle again shown
       • Animal research like this causes permanent damage. Ethical issues & cost benefit. Also how generalisable is it to humans?
     • SCN split in each hemisphere
       • Ventral SCN - easily reset by external cues
         • Desynchronisation caused when ventral and dorsal parts are out of phase
       • Dorsal SCN - less affected by light
     • Pineal gland produces melatonin which inhibits brain mechanisms for wakefulness
     • DeCoursey et al - provided evolutionary advantage, Chipmunks without functioning SCN more likely to die. - Awake & night, making noise attracting predators
   • Exogenous zeitgebers
     • Light
       • Affects SCN and peripheral oscillators
         • Contain cryptochrome (CRY) - sensitive to light
       • Campbell & Murphy - reset circadian rhythms shining light on the back of participants knees
         • Challenged idea of SIffre cave study that light had no effect
         • Not replicated
       • Stevens - artificial light world affects hormone levels, increased cases of cancer
         • Blue light (in electronics & energy saving bulbs) perfect for resetting circadian rhythm. Can set it an hour back
     • Social cues
       • Davidson - mealtimes reset heart & liver cells
     • Biological system control adaptive advantage - difficult to override when faulty
     • Temperature
       • Cold - signal for reduced activity
       • Warm - time for activity (sleep-wake)
       • Buhr et al - temperature changes from circadian clock. In turn this regulates other circadian rhythms
         • Endogenous & Exogenous factors work together to regulate rhythms.
           • Total isolation studies are artificial