Tuesday, October 4, 2016

Blues in the night

Fall is upon us. Everyone in Wisconsin is either eagerly anticipating the lovely fall colors, or are dreading the onset of Seasonal Affective Disorder (SAD). I have already blogged about the color science of the autumn leaves, so, it's probably time for me to blog about the eye, color, and it's tawdry relationship with SAD. Along the way, I will talk about zeitgebers and circadian rhythm entrainment, the spectral response of retinal ganglia, and of course, the supra-chiasmatic nucleus! Hot Damn!

Are you getting sleepy yet?

Today's sleep-inducing lecture begins with melatonin. I think most everyone has heard of it, and everyone has used it, whether they are aware of it or not. Melatonin is the hormone that sends a wake up call to all the team leaders in our body that it's time to start wrapping up the day's activity. Melatonin makes us sleepy.


You can buy melatonin from your favorite drug store, supermarket, or neighborhood dope peddler. It is inexpensive, you can get it without a prescription, and it helps you get to sleep.

Alternately, you can get it from your local pineal gland. If you are a vertebrate, then it is quite likely that you own one of these hot little jobbies. The pineal gland is located kinda in the middle of your brain. It's just a tiny thing, but it'll put you to sleep faster than reading a blog post about seasonal affective disorder. The pineal gland is where the melatonin comes from. But only when the pineal gland is good and ready to give you that mellowing stuff.


But, how does the pineal gland decide when it's time to play Mr. Sandman?


I don't know these women, but I wish I would have done this video!

Getting in the rhythm 

What we need is a clock for Mr. Pineal. No. Check that. Mr. Pineal needs an alarm clock. No. Check that again. Mr. Pineal would do real well to have what my electrical engineering friends would call a phase locked loop. Essentially, this is an oscillator with the added feature of having an active mechanism to keep the oscillator in sync. In this case, the phase locked loop would keep in sync with the rotation of the Earth. By the way, the name of the phase locked loop for the pineal gland is the "supra-chiasmatic nucleus". (Not to be confused with the super-charismatic nucleus, AKA John the Math Guy.)

The job of the supra-chiasmatic nucleus

How does the SCN get synchronized? What is the signal that serves as a zeitgeber?

Aside: I throw in words like "zeitgeber" to make it sound like I know what I am talking about. I have learned through the years that every profession has a relatively small collection of words that act as passwords to get you in the door. Use them correctly in a sentence, and you get to join the club.

Zeitgeber is, of course, a German word. "Zeit" means "time", and "geber" means "giver". This is the official name of "that thing that keeps you in sync with the diurnal cycle".

There have been a lot of suggestions about what the zeitgeber (or zeitgebers) might be. Some obvious guesses are coffee, activity, loud noises, your spouse snoring, a cold or hot shower, a good breakfast, and social interaction. All of these will help us to wake up.

But, sadly, these are not the most effective way to actually reset our alarm clock. In other words, let's say I were to get a real job, one where I had to actually get up before noon every day. If I stop at Starbucks tomorrow at 6:00 AM and have a mocha with three shot of espresso, it will not make it easier for me to get up the following morning. That suprachiasmatic nucleus just keeps chugging along, thinking that 2:00 AM is a decent time to crawl between the sheets.

It took a lot of research, but eventually Science came to the conclusion that light is the primary zeitgeber.

Do you think it unromantic of me to see this sunrise and say "What a glorious zeitgeber"?

SAD and the clandestine pathway

Scientists found many animals that could easily be entrained to the day with light. Originally, it was thought that humans just didn't work this way. It wasn't until the late 1980s that it was found that 2,500 to 3,500 lux was required to activate the SCN. (A typical indoor setting is only a few hundred lux.)

SAD (so the theory goes) is merely what happens when the body is saying "it's time to sleep" when annoyingly happy people are awake being annoyingly happy. SAD is a failure to entrain the SCN during the winter when there is a dearth of sunlight.

Light therapy with full spectrum lights has been used to treat SAD. Historically, treatment of SAD has taken gobs and gobs of light, basically four fluorescent tubes at arm's length. Researchers found that it took a lot of light to entrain a human, and that the light from an incandescent bulb was not particularly effective. So-called "full spectrum" lights became the recommended therapy. Note that the difference between incandescent and full spectrum light is at the blue end. Full-spectrum light has a lot more blue.

It was only fairly recently (1991) that researchers found that the rods and cones in the eye were not the light receptors that kept the SCN in sync with the day. The actual pathway was through the network of nerves in the eye which is called the retinal ganglion. And guess what? The peak response of these puppies is in the blue region, somewhere between 460 nm and 480 nm. This is blue light, by the way.

Today, you can find light therapy boxes that use the much more efficient blue light to treat SAD. It is perhaps coincidental that there are blue LEDs with a dominant wavelength very close to the peak response of the ganglion.

See how annoyingly happy and productive she is?

Avoiding disentrainment

The Foundation for the Research and Investigation of Early Nighttime Diversions (FRIEND) recently published a study that showed that an alarming number of couples have recently forgone previous snuggling activity in preference to checking email and watching stupid cat videos on their cell phones and tablets. [This study involved a random sampling of couples living in my house. The study was published in a blog post from John the Math Guy, entitled "Blues in the night".]



This is a problem. First off, cuz I like snuggling. But perhaps more importantly, cuz many cellphones emit light in that critical region between 460 nm and 480 nm. In other words, the devices stimulate this pathway that tells the SCN that it is still daytime. My closest friend, Jeff Yurek, published a blog post that says that certain devices are less prone to this problem. [Jeff became one of my closest friends when he posted a link to one of my blog posts. I really am that shallow.]

Jeff says that the blue light from quantum dot displays is a bit further into the violet end of the spectrum than the critical region where the ganglion are sensitive. His article calls out the Vizio RS65-B2 as one TV that has a quantum dot display. Who wouldn't want one of these 65" TVs on teh wall in their bedroom?!?

But if you are thinking of something a bit more portable, I just tested my KindleFire HD, and found that it is probably less prone to messing with circadian rhythms.

By the way, I would be more than happy to test anyone's tablet for how susceptible it is to upsetting your biological clock. Of course, I won't guarantee that I will return the device. If I like it, I might just keep it.

4 comments:

  1. Here is a very recent study that corroborates the ideas in this blog:
    http://attivarti.org/v2/morning-and-evening-blue-enriched-light-exposure-alters-metabolic-function-in-normal-weight-adults/

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    Replies
    1. The full article: http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0155601

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  2. Another recent related article:
    https://www.sciencenews.org/article/out-sync-body-clock-causes-more-woes-sleepiness

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  3. Hi John,
    thats an interesting look at and summary of a subject I've come across quite often online.
    Thanks. It provokes thought for sure.
    Your readers might like to look into the link between macular degeneration and LED lighting though, befre exposing themselves to too much of it. (Beyond the virtually unavoidable computer screens, phones and tablets etc.
    http://articles.mercola.com/sites/articles/archive/2016/10/23/near-infrared-led-lighting.aspx?utm_source=dnl&utm_medium=email&utm_content=art1&utm_campaign=20161023Z2&et_cid=DM123657&et_rid=1722578883

    ReplyDelete