When I was studying biology at the University of Groningen, there was a whole department dedicated to chronobiology. It was super fascinating what they did there. They studied the sense of time of people and animals. The sense of time is very important, as it regulates alertness and activity in people and helps animals hibernate and sync their activity with the day and night. The system is also very intricate as it relies on internal time and fine tunes it with external factors like light, noise and activity. The body as a sense of time for the seasons, for the day-night cycle and for measuring seconds.
By telling the time your body can predict when certain events will happen. If you wake up every day around the same time, your body will prepare for this by elevating your body temperature around one hour before you have to wake up. Your sleep cycle is also adjusted to the waking up time. When you eat at regular times, your body will also prepare for this in multiple ways so it can process the food better and make sure that your blood sugar levels don’t spike as much. Telling the time is appearantly so useful that even insects, like fruit flies, have an internal clock that tells them the time.
The biological clock has a strong genetic basis. There are some mutations that will influence the internal clock, making animals get out of sync with the natural day-night rhythm. Studying hamsters with mutations has helped science a lot to understand the internal clock. Laboratory hamsters with the so-called tau mutation have a much shorter circadian rhythm than normal hamsters. When you keep a normal hamster in constant darkness or constant light, it will show its natural circadian rhymth of sleep and activity. This cycle takes around 24 hours and keeps almost in sync with natural day and night alternations. A tau mutation hamster will have a cycle of 20 hours. If it is kept in constant darkness or light it will have much shorter cycles and will become completely out of sync with daylight hours. Often the internal circadian rhythm is masked by external factors, for example light. If a tau mutation hamster is kept in a 12 h darkness, 12 h light cycle it will not become out of sync with daylight hours as it uses the light to adjust its internal clock. This shows that the system is still easy to influence, making genetics only part of the story.
Studying the sense of time can be very useful for people that work in day-night shifts and for medicine. When you work the night shift you upset your biological rhythm, as you are staying awake and focussing while your body is getting ready for sleep. This can affect your performance at work and could have your body maladjusted days after the night shift. Understanding how the circadian rhythm works internally and how it is affected by external factors will benefit the health of a lot of people.
The following TED ED video will tell you a lot about the human sense of time and how it was studied. It’s worth watching!