A conversation earlier this week where I discussed with a colleague that I had only been in my current job for ten months, and was looking forward to having a full year cycle in my new job complete, so I could be aware of the year-round structure and key dates associated with the work I do, got me thinking of zeitgebers and their influence on our lives. Most of my research work in my career to date has examined our brain and body’s physiological system regulatory control mechanisms, in order to understand what regulates our basic human functions and how they are controlled. Most of this work, like in most laboratories around the world, has examined systems within the body, or a specific organ or physiological system in the body, to try and understand its regulation. But of course the activities of our body and our behaviour are not just regulated by internal processes, but also by the need to respond to external environmental or social influences, and zeitgebers are one such important external controller.
A zeitgeber is defined as any external environmental or social cue that ‘entrain’ and synchronizes our body’s functions in a rhythmical way, and therefore ultimately controls its function over a period of time. Examples of zeitgebers include light, temperature, and social interactions. A potent cyclical zeitgeber is the day/night light cycle which sets our 24 hour (circadian) cycle of physiological activity. At a physiological level, the alternating presence or absence of light which is part of the day / night cycle appears to regulate biological ‘clocks’ in our body via receptors in the eye which transmit this information from the external environment to key regulatory areas of the brain, which then adjust our body systems level of activity – usually higher in times of light (daytime), and lower in times of darkness (night). There is also a social zeitgeber ‘loop’ that is induced by the day / night cycle, namely that when it is dark we lie down and sleep, which in an indirect way also slows down our body’s physiological activity levels, and when it is light we become more active and perform our activities of daily living, including routine exercise, and therefore our body’s physiological activity levels increases during the day. Each new day and night cycle causes this increased and decreased physiological activity to be repeated, and therefore becomes a cyclical / rhythmical activity in an ongoing, repetitive manner. Therefore, the day light cycle ultimately ‘enslaves’ or ‘entrains’ our body and social life functions, without us being aware of it’s supreme influence.
Social activity, such as feeding cycles have also been proposed to another important zeitgeber. Daily scheduled feeding, such as eating three regular meals at the same time point each day, induces cyclical changes in the activity of our physiological systems which are required to absorb and use the ingested food. Scheduled feeding also induces anticipatory habituated changes to allow these feeding bouts to occur, such as planning a space in our work day to have a lunch break, and these social changes which allow an individual to feed at similar time points in the day become potent zeitgebers themselves. Zeitgebers do not just work over daily cycles, but can operate over a longer (and shorter) ranges of time. For example, seasonal changes in temperature will cause adjustments in our behaviour at different times of the year, and social activities such as long holidays at specific times of year create different patterns of activity and eating patterns during those specific times of year, in a repetitive and cyclical manner at the same time of year over decades of our lives.
There are also likely to be long term zeitgebers over the course of our entire life cycle. For example, social circumstances and how different stages of our life are ‘regulated’ and ‘marketed’ by our societal infrastructure and expectations are likely to influence how we behave as children, young adults, middle aged or old folk. How active we are and how we change how we behave as we move through our life span may not be related just to the physical ageing processes slowing down the function of our bodies, but may also be related to us ‘fitting into’ the behaviour and behavioural patterns acceptable for each period of our lives as so eloquently described in the the poem by William Shakespeare about the ‘seven stages of man’. So in effect a social zeitgeber may exist which regulates our social and physical behaviour over our entire life cycle, which is not just related to our own body’s age related changes, but also due to society’s expectations and behavioural norms for each specific age we pass through during our lifetime.
Zeitgebers don’t seem to be just a human specific phenomenon. For many years each Sunday morning when I woke up I drove to our local village shop to buy the newspapers and supplies, and took my dog for the drive. After a while doing this, each Sunday morning he (the dog) would be waiting patiently by the door before I arrived for this weekly drive to the shop, which was always astonishing to me from an academic perspective. This example obviously highlights the importance of the need for an awareness of the passing of time / the presence of internal clocks as being essential for the function of social zeitgebers, but in a typical ‘chicken and egg’ scenario, it is not clear if the zeitgebers set the internal clocks that allowed my dog to be aware that it was Sunday morning and therefore time to wait by the door for his weekly drive, or if internal clocks set the social zeitgeber activities by supplying the information to the dog that it was time for him to go and wait for the expected drive. Perhaps like everything, both of these are correct and both the zeitgeber and the internal clock play an interactive role in my dog’s routine weekly behaviour, as it does mine.
So going back to my discussion about looking forward in a few months time to understanding the entire year of my work cycle, the zeitgeber concept would indicate that firstly I / we are perhaps ‘entrained’ by our work cycles in a zeitgeber manner we don’t realize, and secondly that we actually need or want to be so ‘entrained’, and feel somewhat ‘adrift’ if we don’t have the knowledge and security that come with the awareness of being immersed in the yearly patterns of our work / holiday cycles, and therefore that zeitgebers maintain not just our body’s physiological activity, but also our social wellbeing. There is evidence that disruption of zeitgebers / our cyclical routines can lead to psychopathology such as mood disorders and even depression. Equally, there is evidence that psychopathology is also inherent in some of the zeitgeber cycles themselves, for example in the Northern hemisphere there is increased incidence of seasonal affective disorder (depression) during the dark months of winter, and that most folk find the last week before payday in January to be the most depressing time of the year for several obvious reasons. So roll on the completion of my first full year in my current job, so both consciously and perhaps subconsciously I can understand and adjust to the zeitgeber function my work life creates for me, even if this security does come with the worry about who actually is in control of my life, myself or all the zeitgebers that ‘entrain’ me in either daily, monthly, seasonal, yearly, and even lifelong cycles that one just cannot escape from, and from which it perhaps would not be optimal indeed to do so!