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Sleep is an essential function that is needed for survival. The body can rest and recharge during sleep, ready to work at its best the next day. Lack of sleep has been linked to poor cognitive and physical performance, increased illnesses and impaired neurobehavioural functioning.
Sleep and zeitgebers in psychology
The body has mechanisms to ensure that the period of sleeping and being awake is balanced, known as homeostasis. Homeostatic balance of the sleep-wake cycle is important as it prevents people from oversleeping or not getting enough sleep.
Various factors affect the sleep-wake cycle; these are known as endogenous pacemakers and exogenous zeitgebers of sleep.
Sleep is a famous example of a circadian rhythm, flaticon.com/premium-icon
Endogenous pacemakers and exogenous zeitgebers in psychology
Biological rhythms can vary in length, and the sleep-wake cycle is known as a circadian rhythm. Circadian rhythms are cycles of physical, mental and behavioural changes that occur once every 24 hours.
As we mentioned above, two factors affect the sleep-wake cycle:
Endogenous pacemakers
Endogenous pacemakers are genetically determined, internal biological mechanisms that specify biological rhythms.
An example of an endogenous pacemaker is the suprachiasmatic nucleus (SCN), nerve cells that are an internal clock suggested to keep the body in the 24-hour cycle we discussed above. The SCN resides in the hypothalamus.
It can detect light and then regulate melatonin accordingly (the hormone that helps you sleep) through the pineal gland.
Exogeneous zeitgebers
Exogenous zeitgebers are external factors from your surroundings that affect biological rhythms, acting as triggers or prompts to your biological rhythms.
Examples of exogenous pacemakers are the presence of light, temperature, and food.
The two work in tandem, so light, an exogenous zeitgeber, will affect the SCN, an endogenous pacemaker, to regulate your sleep-wake cycle (your biological rhythm). Let's explore that a little further.
Relationship between zeitgebers and sleep
Your endogenous pacemakers and exogenous zeitgebers work in tandem, so light, an exogenous zeitgeber, will affect the SCN, an endogenous pacemaker, to regulate your sleep-wake cycle (your biological rhythm). Let's explore that a little further.
The relationship between zeitgebers and sleep are:
Sleep and Zeitgebers: Light exposure
Light is the main exogenous zeitgeber that affects sleep. There are light-sensitive receptors in the retina (part of the eye). These receptors respond to light and send signals to the brain. For example, the signal may be to wake up. When the sun rises, there is increased light. This is the time when humans wake up and start the day.
Whereas, during and after sunset, there is decreased light. The night period is when humans usually sleep.
Another way light affects the circadian rhythm is via the release of melatonin. The pineal gland, a part of the brain, secretes melatonin. Melatonin is released when the receptors indicate low light levels within your eye (SCN).
Melatonin regulates the sleep-wake cycle. There are high levels of melatonin when you are sleeping and feeling sleepy and low levels during periods of wakefulness.
Plants also react to sunlight. When plants are exposed to increased sunlight, their leaves open to absorb more nutrients to grow healthily. When there is decreased sunlight, plants do not do this to prevent losing too much water at night.
Plants react to sunlight to maximise their ability to absorb sunlight, flaticon.com/premium-icon
Sleep and Zeitgebers: Temperature
During sleep, the body's activity decreases, reducing the work it has to put in to maintain homeostasis.
During sleep, the heart rate is slower, there is less activity in areas such as the stomach, and the body's temperature is lower.
Core body temperature changes in a 24-hour cycle, affecting the sleep-wake cycle. Before falling asleep, the body's temperature lowers. Before waking up, the body's core temperature starts to rise.
The body is preparing for increased activity during wakefulness.
This can be considered an endogenous pacemaker and exogenous zeitgeber as it is affected by internal and external influences.
Sleep and Zeitgebers: Food
The sleep-wake cycle is affected by mealtimes, also known as social cues. As previously mentioned, the body's activity decreases when sleeping. After eating a meal, the digestive system works hard to digest the food. Therefore, during this period, it is difficult to sleep.
When hungry, the stomach sends a signal to the brain telling the body that it needs to wake up so that the body can be fueled.
Food can affect the sleep-wake cycle, flaticon.com
Psychological effects of sleep deprivation
Just as exogenous zeitgebers regulate the sleep-wake cycle, they can just as easily disrupt them.
Someone may start sleeping later or for shorter periods if they eat too much or too close to when they fall asleep.
Other external factors can disrupt the sleep-wake cycle; these include:
Jet lag – when travelling to a new time zone, the sleep-wake cycle is disrupted and is no longer synchronised to the external environment (light)
Shift work – jobs that require early morning shifts or late night shifts can disrupt the circadian rhythm, leading to the sleep-wake cycle not being synchronised with endogenous zeitgebers.
The disruption of the sleep-wake cycle can lead to sleep deprivation; the psychological effects of sleep deprivation are:
Mood issues – anxiety, irritability, low mood, mood swings, and in extreme cases, it can cause psychosis episodes
Impaired cognitive abilities – memory, perception, attention
The onset of sleep illnesses, which can also impact mental illnesses such as anxiety or depression.
Sleep and Zeitgebers - Key takeaways
- Sleep is an essential function needed for survival, and the sleep-wake cycle is an example of a circadian rhythm, occurring once every 24-hours.
- Biological rhythms, such as the circadian rhythm, are affected by internal and external influences. Internal factors are endogenous pacemakers and are genetically determined biological mechanisms. External factors are exogenous zeitgebers, which act as triggers to biological mechanisms.
- An example of an endogenous pacemaker is the suprachiasmatic nucleus, which can detect light and regulate melatonin secretion by the pineal gland.
- An example of an exogenous zeitgeber is light, as it prompts biological mechanisms depending on the levels of light present.
- Both factors can help regulate and disrupt the sleep-wake cycle, and disrupted sleep can negatively affect psychological and physiological health.
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Frequently Asked Questions about Sleep and Zeitgebers
What are examples of zeitgebers?
Some examples of zeitgebers are:
- Light
- Temperature
- Food
What are the four stages of sleep in psychology?
The four stages of sleep in psychology are:
- Stage 1 non-rapid eye movement
- Stage 2 non-rapid eye movement
- Stage 3 non-rapid eye movement
- Rapid eye movement stage
What is the role of zeitgebers in the circadian rhythm?
The role of zeitgebers in the circadian rhythm is to make sure that the biological clock is synchronised with the individual's environment. Disruption can manifest in psychological effects of sleep deprivation, such as impaired cognitive functioning.
Does sleep affect circadian rhythms?
Sleep is an example of a circadian rhythm rather than something that affects it. Circadian rhythms occur once every 24-hours and are affected by endogenous pacemakers and exogenous zeitgebers.
What zeitgebers influence our sleep-wake cycle?
Light intensity during sleep, time of meals and temperature are examples of zeitgebers that influence the sleep-wake cycle.
For example, we know to wake up when it is bright and sleep when it is dark outside.
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