The Zeitgeber: The Subtle Cues We Need To Get Restorative Sleep
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You’ve probably never heard of the term “zeitgeber”, a term created by a scientist named Jurgen Aschoff. The term actually means “time giver” or synchronizer in German, and Dr. Aschoff coined the term after he pioneered research that unveiled our internal biological clocks, and how they tend to sync up with external cues that influence the precise timings of these clocks.
Zeitgebers can be a variety of stimuli, including light, atmospheric conditions, temperature, and external stimuli not caused by natural phenomena such as medication, social interactions, eating and drinking habits, and exercise.
The Natural Rhythm Of The 24 Hour Clock
A cyclical biological process that repeats itself after one cycle that lasts 24 hours, is called a circadian rhythm, usually responding to natural stimuli including daylight and darkness. We have a kind of internal pacemaker, located within the suprachiasmatic nucleus of the brain, or SCN, which regulates the body’s natural biological rhythms. The SCN is influenced not only by natural factors, but processes a combination of external and internal cues to keep our bodies and our brain on a routine schedule provided by the zeitgebers that are playing the notes to this lullaby in the mind.
Not only does the brain respond to light and dark cues, but it also acclimates itself to subtle zeitgebers like the time of day we exercise, eat, and socialize with others, and signals other parts of the brain to release hormones, particularly melatonin and neurotransmitters, which influence when we get sleepy and wind down in preparation for sleep.
Called entrainment, the SCN makes micro-adjustments in a variety of chemical systems within the brain during various times of the day to keep our bodies on a consistent 24 hour pattern which will accommodate and insure that we receive a pretty reliable and predictable amount of sleep.
When the first research began defining the nature and concept of circadian rhythms, it was discovered that humans generally tended to operate on a slightly longer day cycle, about 26 hours. There was a fundamental flaw in the data though because research did not secure the participants in the studies from artificial light, which is dramatically different from natural light.
Light produced by electrical impulses is delivered in a rapidly cycling wave effect, unlike natural light, which is a non-phase, non-pulsating light source. People exposed to excessive artificial light in the evening for example do not tend to be “set” at the ideal points on the circadian rhythm cycle, and this can alter natural sleep times when the body should be shutting down in preparation for sleep.
A Harvard study revealed that the typical range of a natural circadian rhythm cycle is actually pretty precise and very tight. Our biological clocks natural follow and reset themselves in accordance with the natural rotation of the earth, which typically spans about 24 hours and 11-16 minutes in duration.
Many of our biological rhythms, including those related to sleeps well as our level of alertness, mood, and cognitive abilities, are directly synchronized with the body’s internal circadian clock.
To test the mechanism of our internal clocks and to understand just how important these natural cycles are to our bodies, experiments can be conducted where all external cues, such as light, social interaction, and food, are removed so that the body is receiving zero information, literally no zeitgebers, to influence the brain and maintain any cyclical rhythms.
When all of the external cues have been removed, the only remaining cue that the body can use is its own circadian rhythm or internal clock.
Typically, zeitgebers such as light and dark phases, as well as social interactions, are primal cues that directly affect our sleep and wake times. This is tied to millions of years of evolution and conditioning which is hard wired into our DNA, these cues being changes in the threats or rewards present at certain times of the day.
Under these circumstances, the circadian clock alone modulates the body’s biological rhythms. For example, early man was more likely to find food and shelter during the day, and had far less ability to detect predators during the dark of the night, thus being awake tended to be most fruitful during the day and sleep became the safest way to survive during the night.
Secure in a small cave or perhaps at the top of a mountain, we are silent when we sleep, offering no detectable presence to most of our predators. Light and darkness slowly contributed to our physiology, that is being quickly responsive to rising during morning hours and becoming tired and fatigued as darkness fell.
There are a host of zeitgebers, and their influence on an individual is very complex, as each zeitgeber may be interacting with others at any given time. Dr. Aschoff showed that individuals can rely on other zeitgebers if one is missing, say natural light, using others such as social zeitgebers to compensate.
For example, individuals placed in complete darkness for four days did not really differ on a variety of measures, including body temperature, time guessing, and finger tapping, from individuals secluded in an artificially created alternating light-dark environment when both groups were given the same strict time schedule. Researchers concluded that social zeitgebers, like meal times and daily, routine interactions with other people, can establish biological rhythms in ways similar to those of other common zeitgebers like light.
The mere action of going about your day in a routine, regulated fashion also acts as cues to the biological clock we follow. Ritualistic behavior like dinner, winding down with an evening activity, even sex, brushing your teeth, changing into pajamas, and turning off the lights around the house, all are mini-zeitgebers that cue your brain into preparing for sleep.
Psychological Effect When We Modify Our Behavior And Our Zeitgeber Machine
Because our own internal clocks are regulated by a pool of zeitgebers, the loss or disruption of an individual’s regular cache of zeitgebers can be disruptive. When an individual experiences significant changes in zeitgebers, such as being suddenly schedule for shift work, the effects can reduce the ability to secure REM sleep (rapid eye movement) which keeps us from getting the restorative kind of sleep our brain needs for rebooting and recharging.
Another example of the disruption of our zeitgeber mechanism is jet lag, in which traveling great distances causes difficulties with sleep cycles, mood, even appetites. Typically this is due to time zones being flipped, and recovery from jet lag can take days, if not a full week. Just a word of warning- you travel to Asia for example, from the States for business, allow yourself 2-3 days before engaging in any interactions, otherwise you may find yourself not at your best. Such zeitgeber disruptions can also lead to short periods of mental illness, mood problems, diminished cognitive ability, and other issues.
Cognitive Performance And Zeitgebers
Research has shown that the our circadian clocks influences cognitive performance in a wide variety of ways, including reasoning tasks, search ability, verbal cognition and reasoning, and even dexterity with equipment and tools.
During the day, even when are at peak performance and our circadian rhythm and sleep schedules and sleep quality are at peak levels, our level of performance can vary, with tasks involving memory working best in the morning and simple information processing and absorption working best in the evenings.
Studies have discovered that children perform exercises in math best in the morning, whereas teenagers peaks in the evening, just prior to bedtime. But why is this the case?
It’s actually pretty subtle, but this variability has a lot to do with task performance dynamics, which fluctuate wildly during the day, occasionally syncing up, but generally performance is like a multi-faceted diamond, with many surfaces.
Performance ability at various times of the day that are affected by zeitgebers, can include your working memory load and storing ability, which hemisphere of your brain is dominant, your ability to suppress incorrect answers, age, academic prowess, and other factors, many of which fluctuate according to time of day. As a result of these findings, researchers can conclude that factors that disrupt circadian rhythms can also affect cognitive performance.
Disruptions, changes, or omissions of zeitgebers can bring about a negative effect on emotion and mood as well as cognitive performance. The disturbance of biological rhythms by zeitgebers is probably correlated with increased risk for some forms of mental illness. There is evidence to suggest that some people with depression experience disrupted sleep-wake cycles, body temperature, and cortisol levels.
A theory proposed by researchers Ehlers, Frank, and Kupfer in 1988 suggests that destructive life events can lead to clinical depression by disrupting social and biological rhythms and zeitgebers, ultimately leading to sleep disturbance that can cause clinical depression in vulnerable people.
Recent work has also demonstrated that therapy such as exposure to daylight, mild sleep deprivation, and some antidepressant medications, may be effective in treating depression by realigning these rhythms to their natural state.
Such treatments influence an individual’s mood, body temperature, cortisol levels, and melatonin production, all of which are generally not at normal levels or at least irregular in depressed individuals.
The Importance Of Social Zeitgebers
Some experts have suggested that disruptions in biological rhythms found in clinically depressed individuals may actually be caused by previous disruptions in social interactions, which typically function as cues for those rhythms. This may help to explain the relationship between extremely disturbing life events and the onset of mood disorders.
For example, couples that begin to sleep together or newly married couples often need to adjust to each other’s sleeping rhythms when they begin to share a bed. Of course, if they have purchased a new mattress, that is yet another bit of zeitgeber that they must adapt to as well.
This adjustment can be tough at first and can cause disruptions in sleep quality, especially REM sleep, and possibly increase the risk for clinical depression as a result. A number of studies have evaluated whether the loss of a spouse, a significant disruptive life event often which is usually associated with some clinical depression, might lead enhanced depression because of the added effect of disrupted social rhythms. On top of dealing with grief, spouses or partners who lose their loved ones may also be dealing with at least temporary changes in many of their typical and dependable zeitgebers.
For instance, partners who have lost their significant other may quickly be faced with changes in meal times, duties with additional chores, social situations, or simply moving on on a daily basis without their usual conversational partner. Combined, findings from studies on bereaved spouses suggest that bereavement is associated with changes in social rhythms, and symptoms of clinical depression are likely to increase.
If bereaved partners can maintain social rhythms after the death of their spouse, and keep their zeitgebers intact, increased depression is less likely. These conclusions suggest that social interaction stability isn’t completely dependent on life events, but are elements in the big picutre.
A few recent studies have also found a connection between the disturbance of social rhythms and the sudden onset of manic episodes in bipolar disorder, distinguishing between zeitgeber disturbances that lead to clinical depression and those that might cause manic episodes has proven tough to demonstrate.
With bipolar depression, the concept of social zeitgebers as risk factors has been a driving force behind the development of interventions to address this risk. For bipolar disorder, therapies are available that are meant to regulate and normalize an individual’s social rhythms, including scheduled meal times, development of new and existing personal relationships, physical exercise, and other activities that are strictly regulated and placed in scheduled time slots that do not vary.
Seasonal Affective Disorder
Seasonal affective disorder can be exacerbated or brought about as a result of zeitgeber deficiencies, like lack of daylight during the winter months, resulting in a depressed mood. Some research has pointed that melatonin production, which is regulated by circadian rhythms, could be a possible mechanism. Because circadian clocks synchronize human sleep-wake cycles to coincide with periods of the day during which reward potential is highest, during daylight hours, recent studies have determined that daily rhythms in reward activation in humans are controlled by circadian clocks as well, and external influences on those rhythms can alter an individual’s mood.