Ultradian Rhythms (AQA A-Level Psychology): Revision Notes
Ultradian Rhythms
Ultradian rhythms are biological rhythms that last less than 24 hours. Unlike circadian rhythms which follow a 24-hour pattern, ultradian rhythms occur multiple times within a day. The most well-studied example is the sleep/wake cycle, which repeats throughout each night's sleep.
The key distinction is timing: while circadian rhythms follow the Earth's 24-hour rotation, ultradian rhythms are shorter biological cycles that can occur several times within a single day.
The sleep/wake cycle
The sleep/wake cycle represents the daily pattern of wakefulness and sleep experienced by individuals. During sleep, we progress through distinct stages that cycle repeatedly throughout the night. Each complete cycle lasts approximately 90 minutes, and most people experience about five full cycles during a normal night's sleep.
Individual variations exist - some people may have slightly shorter or longer cycles, and the number of complete cycles can vary based on total sleep duration and individual differences.
Stages of the sleep/wake cycle
Sleep consists of five distinct stages that vary in brain activity, physiological effects, and duration:
Stage 1
- Lasts between 5-15 minutes per cycle
- Brain activity shows less than relaxed wakefulness but higher activity than other stages (apart from REM)
- Heart rate slows and muscles relax
- People remain easily woken at this stage
Stage 2
- Length varies between 5-15 minutes per cycle
- Sleep spindles (short bursts of brain activity) occur on EEG outputs during this stage
- The body continues to relax and it becomes more difficult to wake someone
Stage 3
- Brain activity shows fewer sleep spindles and EEG outputs display slow delta waves
- The body relaxes further and people become much harder to wake
Stage 4
- Lasts approximately 40 minutes
- Delta waves (a specific type of brain wave) increase and activity levels become slower than all other stages
- Metabolic rate decreases significantly and digestion slows
- People are very difficult to wake
- Growth hormones are released
REM (Rapid Eye Movement) Sleep
- Initially lasts 15 minutes but lengthens throughout the night, with less time spent in other stages
- Shows more brain activity than any other sleep stage
- Complete relaxation of the trunk muscles
- Irregular breathing and heart rate patterns
- High probability of dreams occurring
The cycle progresses through stages 1-4, then returns to stage 3, then stage 2, before entering REM sleep. This pattern repeats throughout the night, with REM periods becoming longer in later cycles.
Research into ultradian rhythms
Dement & Kleitman (1957) - The relation of eye movements during sleep
Classic Study: Dement & Kleitman (1957)
Participants: Seven adult males and two adult females
Aim: To investigate brain activity changes throughout night-time sleep, particularly examining the relationship between brain activity and dreams
Procedure:
- Participants reported to the laboratory at bedtime and were connected to EEG equipment
- EEG measurements were taken throughout their time asleep, all night
- Participants avoided caffeinated drinks the day before their sleep was investigated
- Researchers woke participants at different stages to investigate dream recall
Key Findings:
- Everyone experienced periods of REM every night
- High levels of dream recall occurred when participants were awakened during REM periods
- When awakened during other stages, very few reported dreaming
- Participants were typically woken between 5-15 minutes into REM sleep
- Brain activity during vivid dreams differed from less clear dreams
- Participants' rapid eye movements during REM sleep reflected the content of their dreams (for example, vertical movements when dreaming about climbing)
Evaluation: Strengths
- This was pioneering research that first documented what occurs during REM sleep
- The study has been replicated many times since 1957, supporting its reliability
- Using EEG provides objective measurement of brain activity, increasing scientific validity
Evaluation: Weaknesses
- The laboratory setting may have created artificial conditions that don't reflect natural sleep patterns
- Small sample size limits the generalisability of findings
- Data collection methods could have caused atypical reactions from participants
Other research findings
Albers et al. (1981) discovered that lesions to the SCN (suprachiasmatic nucleus) in primates led to gradual decay of behaviours controlled by circadian rhythms, but did not affect those controlled by ultradian rhythms. This suggests that circadian and ultradian rhythms operate through different controlling mechanisms.
Van der Veen & Gerkema (2017) used statistical analysis to identify 60 genes associated with ultradian rhythmic activity. This research suggests that ultradian rhythms are controlled by biological, internal factors rather than environmentally determined ones.
Evaluation of ultradian rhythm research
Strengths:
- The development of EEG readings provided psychologists with an objective method for studying sleep behaviour, moving beyond subjective self-reports
- Research has practical applications for understanding sleep disorders and optimising sleep patterns
- Modern genetic research has identified biological mechanisms underlying these rhythms
Limitations:
- Much early research involved animals, creating problems when generalising findings to humans
- Measuring dreams and consciousness presents methodological challenges, as these are subjective experiences
- Laboratory studies may not accurately reflect natural sleep patterns in familiar environments
- Some research findings have been inconsistent - for example, studies show 70% of participants report dreams during NREM sleep, suggesting the relationship between REM and dreaming is more complex than originally thought
Key Points to Remember:
- Ultradian rhythms are biological rhythms lasting less than 24 hours, with the sleep/wake cycle being the primary example
- The sleep cycle consists of five stages (1-4 plus REM) that repeat approximately every 90 minutes throughout the night
- REM sleep is characterised by high brain activity, rapid eye movements, and the highest probability of vivid dreams
- Dement & Kleitman's research established the scientific foundation for understanding sleep stages and their relationship to dreaming
- Modern research suggests ultradian rhythms are controlled by internal biological factors rather than external environmental cues