The Cochlea’s Biological Clock – Updated

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, originally posted on March 10, 2015,  has been updated correcting some inaccuracies and misstatements.  Many thanks from Hearing International to Dr. Hut for his comments.

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For roughly half the world Daylight Savings Time (DST) is a normal transition from winter to spring dstand from fall to winter.  It ushers in the new season and promises extra time at the end of the day, lifting spirits for the new season to come.

While most of us have always thought that DST was invented by  Benjamin Franklin, he merely advocated for rising early, getting your business completed and retiring early to save candles in 18th century France.  Franklin may have invented the concept, but it was a New Zealander, Entomologist George Hudson, who began the world wide DST movement in 1895.  Hudson’s motivations were to give him more time at day’s end to collect bugs and play a round of golf.

The large scale economic, political, energy saving, public safety benefits of DST were first realized in Germany during World War I and caught on in a number of the warring nations that were attempting to reduce lighting demand and save coal as part of the war effort. During WWII, the U.S. observed year-round DST for the same reasons.

A more obscure side benefit of DST is that crime rates usually go down as there is less darkness for criminal endeavors. Farmers set their schedules by the sun and so do their animals, so DST can be simultaneously beneficial as well as disruptive. Of course, the actual dates for the “spring forward” and “fall back” vary from country to country, but usually the changes occur in March and November.

…..But Is it all good?

Depending upon their location most of people enjoy extra sun at the end of the day to collect bugs or play golf  but there are others that report these changes create problems.  dt.jpgConsidering the effects of DST, Professor Till Roenneberg of Ludwig-Maximilians-University in Munich states that, “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 it relates to reproduction but dst5not in the context of DST relative to other biological functions.  According to the National Institutes of Health (NIH) (2012), important body functions, such as sleep, the immune system, and hormone level, are controlled by a biological circadian clock.

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.

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 thedst3 suprachiasmatic nucleus, or SCN. The SCN contains about 20,000 nerve cells located in the hypothalamus, an area of the brain just above where the optic nerves from the eyes cross (click on the picture of the brain for more about the SCN). 

Circadian rhythms have been known 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.

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 ofdt6 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, dtand here the ear’s circadian clock played an important role.  Dr. 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.”  Indeed it could suggest that, in noisy occupations, more hearing loss will occur at night than during the daylight hours.

References:

Handwerk, B. (2015). Daylight Savings Time:  7 surprising things you may not know.  National Geographic.  Retrieved May 16, 2016.

Hut, R. (2016).  Personal communication, May 14, 2016.  Comments to Hearing International.

Karolinska Institutet. Circadian clock in the ear: Time of day of hearing damage affects healing. ScienceDaily,  27 February 2014. Retrieved March 10, 2015

National Institute of General Medical Sciences (2012).  Circadian rhythms fact sheet.  Retrieved March 10, 2015

Wolverton, M. (2013).  Living by the clock: the science of chronobiology.  Retrieved March 9, 2015

Reinberg, S. (2014). The body’s clock never adjusts to daylight savings time.  Retrieved March 9, 2015:

Images:

Bartlang, M. (2012). Daylight-dependent effects of chronic/intermittent stressor exposure on behavior, physiology, immuniology and the internal clock:  Retrieved March 10, 2015

Video:

Phys Post Press Channel (2012).  Suprachaismatic nucleus.  You Tube  Retrieved March 10, 2015

About Robert Traynor

Robert M. Traynor, Ed.D., MBA is the CEO and practicing audiologist at Audiology Associates, Inc., in Greeley, Colorado with particular emphasis in amplification and operative monitoring, offering all general audiological services to patients of all ages. Dr. Traynor holds degrees from the University of Northern Colorado (BA, 1972, MA 1973, Ed.D., 1975), the University of Phoenix (MBA, 2006) as well as Post Doctoral Study at Northwestern University (1984). He taught Audiology at the University of Northern Colorado (1973-1982), University of Arkansas for Medical Sciences (1976-77) and Colorado State University (1982-1993). Dr. Traynor is a retired Lt. Colonel from the US Army Reserve Medical Service Corps and currently serves as an Adjunct Professor of Audiology at the University of Florida, the University of Colorado, and the University of Northern Colorado. For 17 years he was Senior International Audiology Consultant to a major hearing instrument manufacturer traveling all over the world providing academic audiological and product orientation for distributors and staff. A clinician and practice manager for over 35 years, Dr. Traynor has lectured on most aspects of the field of Audiology in over 40 countries. Dr. Traynor is the current President of the Colorado Academy of Audiology and co-author of Strategic Practice Management a text used in most universities to train audiologists in practice management, now being updated to a 2nd edition.

1 Comment

  1. On a larger spatial perspective, it may boil down to repair mechanisms like calcium production to repair the ossicles when physical damage takes place due to loud sounds. The factors like eating time, expending energy time (work), resting time, playtime, and perhaps the most important of all, thinking time may be part of the total equation of daily life activity.

    Our daily functions are not controlled by time of day. There are many people who work, unaware of time changes, in complete darkness, and spend more of their waking time in a timeless environment. What circadian rhythms do they follow biologically?

    The subject is relevant, because some of us will be traveling to distant planets, without atmospheric pressures similar to Earth, and where these pioneers will be involved in tasks that may be affected by such rhythms acquired on Planet Earth.

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