Biopsychology 6- biological rhythms (circadian, infradian and ultradian) and endogenous pacemakers and exogenous zeitgebers

Biological rhythm

Patterns of changes in body activity that occur over cyclical time periods.

Circadian rhythm

A rhythm lasting about 24 hours (e.g., sleep–wake cycle).

Ultradian rhythm

A rhythm with a cycle shorter than 24 hours (e.g., sleep stages).

Infradian rhythm

A rhythm longer than 24 hours (e.g., menstrual cycle, seasonal affective disorder).

Sleep cycle

An ultradian rhythm consisting of stages of NREM and REM sleep.

Endogenous pacemakers

Internal biological clocks regulating rhythms (e.g., suprachiasmatic nucleus).

Suprachiasmatic nucleus (SCN)

The main internal clock controlling circadian rhythms; responds to light levels.

Exogenous zeitgebers

External cues that help regulate biological rhythms (e.g., light, social cues).

Light as a zeitgeber

Resets the SCN and helps maintain the sleep–wake cycle.

Social cues

External factors such as meal times or routines that help entrain biological rhythms.

What are the strengths of the circadian rhythms theory?

      + Strong research support

• Siffre & Folkard show importance of internal & external controls.
  + Practical applications

• Chronotherapeutics (timing of medication), shift work understanding.

What are the limitations of the circadian rhythms theory?

– Case study evidence

• Small samples → low generalisability.
  – Individual differences

• Age & chronotypes vary (larks vs owls).
  – Artificial conditions

• Cave studies lack realism → reduce validity.

What are the strengths of the ultradian and infradian rhythms theory?

+ Research support for ultradian rhythms

• Dement & Kleitman → scientific EEG evidence.
  + Evolutionary explanation

• Menstrual synchrony may have historically increased reproductive success.

What are the limitations of the ultradian and infradian rhythms theory?

       – Methodological issues

• Menstrual synchrony studies criticised for confounding variables (diet, stress).
  – Individual differences

• Sleep cycles vary significantly between people.
  – Pheromone research criticised

• Questionable reliability.

What are the strengths of the endogenous pacemakers and exogenous zeitgebers theory?

+ Research support for SCN

• Animals with SCN lesions show disrupted rhythms.
  + Support for zeitgebers

• Campbell & Murphy → light influences cycle even without eyes.

What are the limitations of the endogenous pacemakers and exogenous zeitgebers theory?

       – Animal research problems

• SCN lesion studies lack generalisability/ethical issues.
  – Case study limitations

• Campbell & Murphy poorly controlled; may not replicate.
  – Overstated separation

• Pacemakers & zeitgebers interact → difficult to isolate.