Occasionally at Hearing International we receive comments and corrections from readers. Thanks to Dr. Roelof A. Hut, Associate Professor of Chronobiology at of the University of Groningen, Netherlands this article has been updated correcting some inaccuracies and misstatements. The reader is directed to the updated version published May 17 2016.
Many thanks from Hearing International to Dr. Hut for his comments.
In the US this week we are in our first week of Daylight savings time. Many individuals report that they are totally upset by the change of single hour. When the effects of daylight savings time are considered, Roenneberg (2007) states, “When you change clocks to daylight saving time, you don’t change anything related to sun time; this is one of those human arrogances — that we can do whatever we want as long as we are disciplined. We forget that there is a biological clock that is as old as living organisms, a clock that cannot be fooled. The pure social change of time cannot fool the clock.”
Roenneberg further states, “The circadian clock does not change to the social change and during the winter, there is a beautiful tracking of dawn in human sleep behavior, which is completely and immediately interrupted when daylight saving time is introduced in March. It returns to normal this year when standard time returns in November.”
The Biological Clock
We have all heard of the proverbial “biological clock.” As generally discussed, the biological clock is often related to reproduction and not to daylight savings time or to other biological functions. It is contended, according to the National Institutes of Health (NIH) (2012), that important body functions, such as sleep, the immune system, and hormone level, are controlled by a biological circadian clock. These circadian rhythms are physical, mental and behavioral changes that follow a roughly 24-hour cycle and respond primarily to light and darkness in an organism’s environment.
These rhythms are found in most living things, including animals, plants and many tiny microbes, and the study of circadian rhythms is called chronobiology. These biological clocks that control circadian rhythms are groupings of interacting molecules in cells throughout the body. A “master clock” in the brain coordinates all the body clocks so that they are in sync. The “master clock” that controls circadian rhythms consists of a group of nerve cells in the brain called the suprachiasmatic nucleus, or SCN. The SCN contains about 20,000 nerve cells and is located in the hypothalamus, an area of the brain just above where the optic nerves from the eyes cross.
Circadian rhythms have been known about for centuries, but during the 20th century it became clear that there were important connections between the ticking of the clock and the workings of life, even within our own bodies. Scientists discovered that blood pressure varies naturally by time of day and began to think about issues such as sleep, hormonal cycles, and work schedules, especially as industrialization and the modern age ushered in a 24-hour society dependent on shift work.
The late Mitchell Lazar, M.D., Ph.D., the Sylvan H. Eisman Professor of Medicine at the University of Pennsylvania, and director of the Institute for Diabetes, Obesity, and Metabolism, cites the work of scientists such as Franz Halberg at the University of Minnesota, who coined the term “circadian” (meaning a 24-hour period), and Colin Pittendrigh at Princeton and Stanford, who organized the first dedicated scientific symposium on biological clock, and found that “the clock” was in the suprachiasmatic nucleus or SCN.
Lazar explains, “The way we interact with our environment is that light hits our retina, which is part of the brain, the retina sends a neural signal to the SCN that more or less says it’s light out or it’s not light out. That helps to entrain the clock in the SCN, and then to the simplest and most primitive one-celled organisms like cyanobacteria. In essence, rather than being ruled by one big clock whose bell tolls throughout the entire organism like Big Ben in the streets of London, every living thing is a clock shop, containing a multitude of timepieces ticking away in unison – but not always in synchronization. Just as rhythm is a fundamental part of music, it’s also an essential part of life. But while it’s quite possible to have music without rhythm, life is impossible without the presence of regular, recurring time cycles.”
OKAY….But What About The Ear?
There are always questions about the ear and how damage can occur to hearing. Researchers have identified a “biological clock” in the ear that controls how well hearing damage may heal, a finding that may help develop new treatments for people with hearing loss. While it may or may not have much to do with daylight savings time, a team of researchers at Karolinska Institutet have discovered that the ear’s biological clock is controlled by genes known to regulate circadian rhythms. One of these genes was found to cycle in the cochlea of mice over several days in a pattern that followed the hours of the day making the mice especially susceptible to noise exposure at certain times. By measuring the activity of the auditory nerve, the researchers found that mice exposed to moderate noise levels during the night suffered permanent hearing damage while mice exposed to similar noise levels during the day did not. The ability to heal after hearing damage was therefore linked to the time of day during which the noise damage occurred, and here the ear’s circadian clock played an important role. Barbara Canlon, professor of auditory physiology at the Department of Physiology and Pharmacology at Karolinska Institutet, feels that this fundamental discovery “opens up an entirely new field of research and reveals some of the mysteries behind the unfamiliar auditory functions.”
Karolinska Institutet. Circadian clock in the ear: Time of day of hearing damage affects healing. ScienceDaily, 27 February 2014. Retrieved March 10, 2015: .http://www.sciencedaily.com/releases/2014/02/140227125249.htm
National Institute of General Medical Sciences (2012). Circadian rhythms fact sheet. Retrieved March 10, 2015: http://www.nigms.nih.gov/Education/Pages/Factsheet_CircadianRhythms.aspx
Wolverton, M. (2013). Living by the clock: the science of chronobiology. Retrieved March 9, 2015: http://www.uphs.upenn.edu/news/publications/PENNMedicine/files/spring_2013_living_by_the_clock.pdf
Reinberg, S. (2014). The body’s clock never adjusts to daylight savings time. Retrieved March 9, 2015: http://abcnews.go.com/Health/Healthday/story?id=4509150&page=1
Bartlang, M. (2012). Dayligh-dependent effects of chronic/intermittentstressor exposure on behavior, physiology, immuniology and the internal clock: Retrived March 10, 2015: https://www.elitenetzwerk.bayern.de/elitenetzwerk-home/forschungsarbeiten/lebenswissenschaften/2012/bartlang/
Phys Post Press Channel (2012). Suprachaismatic nucleus. You Tube Retrieved March 10, 2015: https://www.youtube.com/watch?v=vOuQdTXxPsU
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