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You are here: MEDICA Portal. Our Topics in 2009. Topic of the Month June: Neurology. Sleep.

„There Is no Wrong Rhythm just a Different One“

„There Is no Wrong Rhythm just a Different One“

Photo: An owl sitting with the sun going down in the back spoke to Christian Cajochen of the Centre for Chronobiology of the University of Basel about a buzzer as small as a grain of rice, the power of the biological clock and win-win situations for owls and employers. Mister Cajochen, you have found a place in the human brain that ultimately rescues the late risers from the stigma of lazyness. Has the German club of long sleepers already given thanks to you?

Christian Cajochen: No, they did not. Yet people who get up late are in fact not necessarily long sleepers or lazy. Evening types go to bed late and get up correspondingly late. For them, the saying "The early bird catches the worm" simply does not apply. You devide persons in morning and evening types. What does that mean exactly?

Cajochen: That means people whose day starts very early or very late. It accounts for 20 percent of the population. Normal types get up around eight o'clock. Extreme morning types feel at five in the morning just as the normal type feels at eight. For extreme evening types, the day in part only starts at two o'clock. In cooperation with colleagues from Belgium, you have discovered that evening types have a buzzer inside the brain that goes off loudly at the end of the day. In these late hours, evening types therefore are much more capable of performance than morning times.

Cajochen: Yes, we have measured this with functional magnetic resonance imaging. The participants of our study for instance had to remember a combination of numbers or had to press a key as quickly as possible when a certain object appeared on a computer screen. At the same time, the scanner has imaged the brain. In the morning, the brain regions needed for these tasks showed the same activity, no matter what type. Ten hours later, however, they were much more active in the evening than in the morning types. Thus, the evening types performed better in the evening, but the morning types did not so in the morning?

Cajochen: Exactly, contrary to our expectations. We thought that the buzzer rings in the morning in the brain of the morning types, so that, then, they show the better achievements. At the time we measured, though, - one hour and a half after the participants woke up by themselves –there was no difference between the two types. Nevertheless, the early risers might have a similar buzzer. If we had tested them at another time, for example around five in the morning or already 15 minutes after waking up, we maybe had found one. We do not know that. The searching continues. Sounds as if evening types might have an advantage.

Cajochen: Our results might mean that after ten hours they have a qualitatively better time than the morning types. However, more tests are necessary to prove this. All our test persons were allowed to live according to their own rhythm during the trial. Yet, morning types languished the last six hours of their day and were no more than ten hours really high-spirited. Evening types, in contrast, could remain wide awake up to 16 hours. This kind of buzzer, as you call the active region in the brain, does not literally ring. What exactly happens in this part of the head?

Cajochen: Each human being has a biological clock, a pacemaker inside the brain, similar to the heart pacemaker. Just as the heart pacemaker dictates the rhythm for the heart, does the biological clock conduct the sleep-wake-cycle. This internal clock is situated two to three centimetres behind the root of the nose, is as small as a grain of rice and consists of about 10,000 of neurons that start to swing in a 24-hour rhythm. The neurons are active for around 16 hours and communicate with those regions of the brain that keep our body awake, as if commanding: "Stay awake!" The remaining eight hours we sleep.

Photo: A lark standing in the grass
In old age, everybody's biological clock leans towards the larks'
rhythm; © Ralf Zierold/ If every person has this body clock: What exactly is the difference between the types?

Cajochen: The process in the brain is basically the same in normal, morning and evening types. But the reveille of the evening type is sent considerably longer and stronger during the evening hours, clearly predominating the pressure to sleep that accumulates over the day. These strong signals in the evening can be called a buzzer that distinguishes the evening type compared to the others. The morning types, on the contrary, are dominated quite early by the pressure to sleep: the reveille of the internal clock is sent but weak and shorter so that the longing for sleep prevails. Does the buzzer of the so-called owls ring at the wrong time?

Cajochen: There is no wrong rhythm just a different one. It is individually different just as we have blond, brown or red hair. Extreme morning types will never become evening types, and the opposite way around, because the biological clock is pretty much influenced by out genes. By habituation, one can adapt a little, that is get up around one or two hours earlier or later than the internal clock dictates - yet no more. Beyond this, one can live only for a short time against the biological clock. This is very exhausting in the long run and people will always come back to their own rhythm. So, once a night owl, always a night owl?

Cajochen: Yes, exactly. Only in high age, the internal clock modifies and leans towards the larks' rhythm. Then, many night owls become "evening owls". Is it very unhealthy to live contrary to the own biological rhythm?

Cajochen: Obviously, it does not result in death if night owls get up at seven o'clock in the morning. Therefore, this is difficult to judge. However, the night shift work which runs against the biological rhythm of most people is definitively unhealthy. This is officially recognised. The World Health Organization (WHO) has classified night shift jobs as cancer-causing because researchers have found out that former night workers have a raised breast cancer risk. It is defininitely not nice to wake up bleary-eyed always again. So, what do you advice owls that have to start working drowsily, early in the morning?

Cajochen: To start looking for a new job that allows them to get up later. It would be great if time agreements with the employers would achieve acceptance. If the employee started working not until ten o'clock and then worked for the usual eight hours, he would be happier, less tired and more productive. A win-win situation for employees and employers. Thank you very much for the conversation.

Cajochen: You are welcome. Sleep well!

The interview was conducted by Anke Barth.


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