Ultradian rhythms

Ultradian rhythms AO1

• Cycles that occur more than once every 24 hours

• Influenced by exogenous zeitgebers & endogenous pacemakers

• Work together as a blended system

• Example - stages of sleep

Stages of sleep AO1

• Alternates between REM (rapid eye movements) & NREM every 90 mins 

• Stage 1 - light sleep

• Stage 2 - slightly deeper sleep

• Stage 3 - deep sleep (slower delta waves)

• Stage 4 - deep sleep

• Stage 5 - REM - body is paralysed & brain activity resembles that of an awake person, associated with dreaming 

Ultradian rhythms strengths AO3

• P - case study support

• E - Randy Gardener stayed awake for 11 days. While he experienced many problems, such as blurred vision & disorganised speech, he coped rather well after his sleep deprivation. After, he slept for just 15 hours & recovered 70% of stage 4 sleep & 50% of REM, indicating that sleep cycles can compensate for lost sleep

• T - This shows homeostatic flexibility: the body prioritises essential stages of the sleep cycle (e.g., REM) to restore physiological balance & the variable nature of this ultradian rhythm

• P - practical applications

• E - Understanding the structure and timing of ultradian rhythms allows clinicians to identify abnormal sleep patterns and diagnose sleep disorders such as Insomnia, where Individuals may show fragmented or shortened sleep cycles, especially reduced Stage 3/4. This has helped develop treatments, such as cognitive behavioural therapy for insomnia (CBT-I) and chronotherapy which can help adjust patients’ ultradian sleep patterns. Also, kleitman proposed the BRAC Theory, where humans experience alternating periods of high alertness and performance (first ~60–70 minutes) followed by fatigue and reduced focus (~20 minutes). This has been applied in education to help students revise, by breaking revision into 90-minute “focus sessions” followed by short breaks mirrors natural cycles, maximising concentration and retention..

• T - research has real world relevance & has been applied to benefit all areas of society

Ultradian rhythms limitations AO3

• P - individual differences 

• E - Tucker studied ppts sleep patterns in a controlled laboratory environment using polysomnography. Ppts showed significant differences in the duration of stages, suggesting that the 90 min cycle is only an average & can be influenced by individual differences. For example, research has shown age can affect sleep cycles as infants tend to have shorter cycles (50 mins) with more REM whilst the elderly have less deep stages. Environmental & lifestyle factors can also effect, such as caffeine & stress which can increase cortisol & reduce REM & deep sleep. 

• T - individual differences challenge deterministic models of ultradian rhythms & support an interactionist model, where innate biological mechanisms set a general framework (e.g., 90-minute cycles), but environmental factors can influence this. This provides support for endogenous pacemakers & exogenous zeitgebers acting as a blended system. 

• P - research is conducted in lab settings

• E - lab sleep studies require participants to sleep in an unfamiliar setting, often in a small, controlled room with monitoring electrodes attached to their head and face. This environment is highly artificial compared to a person’s normal sleeping conditions at home. The unnatural setting can disrupt normal sleep patterns, leading to what’s known as the “first-night effect” — people often sleep worse or differently the first night in a sleep lab. Also it could cause anxiety or discomfort, which may alter their ultradian rhythm. 

• T - whilst there is high internal validity due to the control of extraneous variables (eg noise & light), ecological validity may be low & findings may not reflect typical everyday sleep which limits the extent that findings can be generalised