SITNFlash

Greetings SITN members!

It’s September, and that is our favorite month here at Science in the News as it means the start of our free fall seminar series! The series kicks off on Sept 21st with a special seminar entitled “Making Sense of Science in the News”. Have you ever wondered how to interpret the science headlines you see in the news, or wondered how to judge for yourself whether to believe all the hype about new diets and drug treatments? By understanding how scientists design and interpret studies, as well as what the limitations of those studies are, you will be well-equipped to make informed judgments about the headlines you see everyday.
A full list of the seminar topics for this season is included below. We hope to see you this fall, and remember, you can always stay up to date on our seminar series by visiting our website at http://sitn.hms.harvard.edu/.

Enjoy!

--The SITN Staff

Are you an early bird? Or a night owl? Regardless of which term best describes your daily, or circadian, rhythm, chances are you find yourself sometimes wishing that you could change your sleep-wake cycle. With the start of a new school year, young night owls may struggle to synchronize their internal clocks with an early morning schedule, while those in the working world may have a similar battle when attending an early meeting. Likewise, early birds may have a hard time staying up at night to complete their work and studies. What is the biological basis of our internal clock? And how do we reset our internal clock when it gets out of sync with our lives?

A Clock in the Brain

A small region of our brain called the hypothalamus helps to control many of our so-called autonomic functions, which are body functions not requiring thought. One such autonomic function is circadian rhythm, our daily cycle of sleepiness and waking. A small group of brain cells within the hypothalamus function as our internal clock, and these are collectively known as the suprachiasmatic nucleus (SCN). SCN cells display an oscillating pattern of electrical activity, which is based on the changing levels of particular proteins. These protein levels change approximately every 24 hours, and this is what keeps time for our internal clock.

Scientists do not completely understand how the oscillating activity of the SCN is translated into circadian rhythm. However, we do know that a number of hormones are affected by the internal clock. One of the most interesting of these is melatonin, which has been nicknamed “the hormone of darkness” because melatonin levels are highest during the night and lowest during the day. Administering melatonin to patients seems to induce sleepiness, as a result of shifting their circadian rhythm. However, not all studies agree on the effects of melatonin. The current thought is that melatonin plays an important role in regulating circadian rhythm, but it is not the only player receiving directions from the internal clock.

Let There Be Light

How do we reset, or entrain, our internal clocks to adjust to different schedules or time zones? As discussed above, some studies have suggested that changing the levels of melatonin in your body can adjust your sleep cycle. Exercise and social stimulation have also been shown to regulate circadian rhythm. However, the most studied and arguably most important external factor is light.

Photosensitive cells in our eyes called rods and cones detect light for vision. For a long time, it was assumed that these cells transmit information from the light to the SCN. However, researchers had observed that blind mice were just as responsive as mice with normal vision when light was used to reset their internal clocks, suggesting that rods and cones were not the answer.

Then in 2002, a flurry of publications reported that the light receptors that affect our internal clock are different from those that detect light for vision. These studies closely examined another type of eye cell, called the ganglion cell, which normally relays messages from the rods and cones to the brain. A small percent of these ganglion cells were found to be responsive to light, and notably, these cells connect directly to the SCN, thus establishing a direct link between light and our internal clock.

Interestingly, ganglion cells were found to be most responsive to blue light, consistent with other studies that found blue light to be the most effective (relative to white light or other colors) at resetting the internal clock. This provided further evidence that these cells are indeed responsible for receiving and transmitting the information into the brain.

Light Therapy

Light has been used to successfully influence the sleeping patterns of people with circadian rhythm disorders, whose biological clocks are out of sync with a “normal” day and night. It has also been effective with people suffering from winter depression, also known as seasonal affective disorder (SAD). SAD is a subtype of clinical depression in which patients have increased episodes of depression during the winter months. Although SAD is not strictly a circadian rhythm disorder, it is believed to have a circadian rhythm component. Phototherapy, in which patients are exposed to an intense fluorescent light, is one treatment for this disorder and can have significant benefits for a reported 50-80% of SAD patients. The phototherapy treatments are believed to help reset the internal clock, thus preventing the onset of depression.

Your Clock and You

In our modern world, in which we wake to blaring alarm clocks and stay up late into the night, it is interesting to think about how our lifestyle affects our internal clocks. If our circadian rhythm is naturally regulated by light, what happens when we spend the daylight hours inside an office building, shielded from the sunlight? What happens when we spend the evening hours under artificial lights? Computer screens may be particularly rich in blue light emissions, which could reset our clocks as we browse the internet or write e-mails at night. These perturbations in our natural light cycle most likely affect our sleeping patterns and potentially our long-term health and well-being. As we learn more about the gears and springs that constitute our internal clock, we will discover not only better ways to cope with jet lag and other circadian rhythm disorders, but also develop an even greater appreciation for the complex regulatory networks occurring in our bodies all the time, day and night, even while we sleep.

-- Stephanie Wai, Harvard Medical School

Primary Articles

Berson, DM. Strange vision: ganglion cells as circadian photoreceptors. Trends in Neurosciences. June 2003. 26(6): 314-320.
Barinaga, M. CIRCADIAN CLOCK: How the Brain's Clock Gets Daily Enlightenment. Science. February 8, 2002. 295:955-957.
Lewy AJ et al. The circadian basis of winter depression. PNAS. May 9, 2006. 103(19): 7414–7419.

For More Information:

Laboratory webpage of Dr. Roberto Refinetti, a circadian rhythm researcher at the University of South Carolina : <http://www.circadian.org>
Cleveland Clinic article about circadian rhythm disorders: <http://www.clevelandclinic.org/health/health-info/docs/3700/3712.asp?index=12115>
Medline Plus article about Seasonal Affective Disorder: <http://www.nlm.nih.gov/medlineplus/seasonalaffectivedisorder.html>
Article about how light affects circadian rhythm: Raloff, J. Light Impacts. Science News.  May 27, 2006 . 169 (21): 330.
<http://www.sciencenews.org/articles/20060527/bob9.asp>

Here's the schedule for the 2006 lecture series! The series kicks off on September 21st with an introductory lecture entitiled "Making Sense of Science in the News," with a new lecture every week thereafter on a wide range of topics in the headlines, from mental health to global warming. Lastly, this year we will be continuing to offer or lectures on two night at two locations, so feel free to attend the seminar that is more convenient for you! Here is the full schedule:

Of course, for the latest updates, check http://sitn.hms.harvard.edu/!