6 4 biological rhythms

Circadian rhythms operate on a 24-hour cycle, which is reset by levels of light.

c. The SCN (suprachiasmatic nuclei) in the hypothalamus detect the level of light present. The SCN then uses this information to coordinate the activity of the entire circadian system by either triggering sleep or telling the body to wake up.

Melatonin plays a role in triggering sleep by responding to a decrease in the levels of light?

False. Shift work and jet lag have been found to lead to the desynchronisation of circadian rhythms and can lead to adverse cognitive and physiological effects.

d. Siffre's research (the 'cave study') supports the idea that the sleep-wake cycle has a duration of just over 24 hours.

b. Siffre had some artificial light sources throughout his procedure which decreases the study's validity.

Infradian rhythms are cycles that last more than 24 hours. E.g., the menstrual cycle.

a. McClintock & Stern conducted research into infradian rhythms and found that 68% of the participants' menstrual cycles had synchronised.

b. Each woman's personality is not a potential extraneous variable that could compromise the findings of McLintock & Stern.

Ultradian rhythms are cycles which occur under 24-hours. E.g., the individual cycles of sleep.

False. Stages 3 and 4 consist of the delta waves of deep sleep. Stages 1 and 2 are known as the sleep escalator.

REM sleep occurs in stage 5.

True. Dement & Kleitman's findings are difficult to generalise due to the small sample of 5. This means that the findings lack external validity.

Dement & Kleitman controlled for possible confounding variables of participants having alcohol or caffeine before the study, which means that their research is high in validity.

Endogenous pacemakers are the internal mechanisms that determine the biological rhythms of the body.

False. **Endogenous pacemakers can be affected by the external environment. E.g., changes **in light levels.

The pineal gland, located deep in the centre of the brain, detects light sources and is implicated in circadian rhythms and melatonin secretion.

The SCN sends signals to the pineal gland, which increases the secretion of melatonin at night, helping to induce sleep.

b. Morgan's (1995) research using hamsters found that the SCN is a significant endogenous pacemaker.

True. Morgan's research is flawed due to its use of hamsters as subjects. Research using hamsters is not generalisable to humans.

Exogenous zeitgebers are any factors in the sleep-wake cycle that act as external cues to either wakefulness or sleepiness.

Light is the main exogenous zeitgeber.

d. A night light is not a social cue, which could act as an exogenous zeitgeber.

a. The alignment of behaviours such as waking, eating meals, working to a regular sleep-wake cycle is known as entrainment.

False. In Campbell & Murphy's study, sleeping participants were woken throughout the night, and a light pad was shone onto the back of their knees. This is a strength of the study, as it increases the validity of the role of exogenous zeitgeber in the sleep-wake cycle.

a. Campbell & Murphy's findings have not been replicated in any subsequent studies which reduces their reliability. If a study cannot be replicated then it cannot be checked for consistency.