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About Arcascope

Welcome to Arcascope

Here’s the thing about the name:

I wanted to capture what I thought was most exciting about our company.

Sure, you can sleep better by taking care of your circadian rhythms, but circadian rhythms are about a lot more than just sleep

And yep, we’re a circadian rhythms company, but we’re one founded by people who are (primarily) mathematical biologists. 

Rather than trying to figure out what time is in a person’s brain with a gold standard test (for instance, by taking repeated saliva samples for hours in the dark), we use math models to infer what’s most likely to be going on in their brain, given all the inputs that have gone into it. 

Rather than trying to estimate their internal time from a single measurement or number, we use lots of data, collected on the timespan of weeks to months. 

In a sense, we’re using our algorithms to see inside a black box: letting us predict what’s going on in your head, without the need for invasive testing. That’s what I think is most cool about our tech. 

Categories
Circadian Sleeping Troubles Technology

Interview with Dr. Cathy Goldstein

We sat down to talk with Dr. Goldstein on what she sees as the future of wearables in the sleep clinic. Enjoy!

Thank you for taking the time to meet with me today! Could you take a minute to introduce yourself and say a little about what your job is?

Cathy Goldstein, MD. I’m a neurologist, Associate Professor of Neurology here at Michigan Medicine, and my clinical practice is entirely in sleep medicine.

You’ve done work with [Arcascope CEO] Olivia on wearables, and you’re heavily involved in the AASM and consumer sleep technologies. Where do things stand today for consumer sleep technology and wearables, and where do they need to go?

These devices really started becoming prominent about 8 years ago. I remember I was right out of my fellowship at that time, and I thought, wow, these will be so awesome for when a patient sees me in the clinic: I have all these questions about their sleep and sleep timing, and how they sleep on the weekdays vs weekends vs vacation, and they’re in the position of having to try and remember what their problems have been over the long time they’ve been waiting to see me. 

And the problem with a sleep log [that someone fills out manually] is that it’s hard to keep up with every day. In this busy world, you need more of a passive degree of tracking, particularly over time. So when wearables came out I was like, wow, you know, wouldn’t it be cool if when the patient shows up I can just take a look at their data in the last six months and see their sleep patterns. 

The problem as far as adoption has gone, is that we don’t know how accurate they are at tracking sleep. So, there’s a medical grade version of consumer trackers called “actigraphy”, although they’re not completely accurate, we KNOW how accurate they are. And so, particularly in science and medicine, what is known is better and less scary—even if the performance isn’t great— than the unknown. 

There are a lot of unknowns in regard to consumer-targeted sleep tracking because there’s not a lot of peer-reviewed literature about the performance of these. It’s growing, but even when the accuracy does get reported in a paper, oftentimes the algorithms change with updates, or the hardware changes a little bit with each iteration. The big thing is—we just don’t know. And that’s really prevented adoption in research and clinical practice, unfortunately. 

What are the biggest misconceptions about sleep wearables that you see out in the world?

The biggest misconception is that they’re totally inaccurate, that they’re inferior to actigraphy for some reason, because the data that we have so far doesn’t necessarily suggest that. For many of these devices, we just don’t know, but the ones that we do know about appear to perform similarly. 

I’d say the other misconception is people say, “My watch tracks my sleep.” Your watch doesn’t track sleep: your watch tracks your heart rate or your pulse, and your watch tracks movement. And then, math estimates your sleep from that device. So, that’s a big misconception of people telling me in the clinic, “My device is telling me I don’t have REM, so my sleep is really bad.” Sleep stages like REM, NREM  are polysomnography EEG constructs. So, to use a consumer wearable sleep tracker’s components of dream sleep, light sleep, deep sleep, interchangeably with PSG-defined states— we’re just not there yet in my opinion. 

I do think the estimates are getting better, and they do use properties of heart rate variability that we know change in the different sleep stages, but still, those [stages] are defined by brainwaves and eye movements. So, it’s very hard to recapitulate that. The question is, “Do we even need to track that on a daily basis?” What we’re really looking for, and what the clinical and research world wants, is to track on a longitudinal basis— objectively— just sleep-wake patterns day to day.

How do sleep trackers fit in with sleep clinics right now?

People sometimes think that doctors just don’t want to look at sleep wearable data because we don’t like it—that’s not true. A lot of us love seeing this data and love seeing sleep patterns over time, particularly if a patient can tell me “Hey you know, you treated my sleep apnea with this CPAP machine, and look at the change in my wearable tracked sleep.” One of the massive problems, though, is that clinical practices are really, really busy. We have a lot of patients that need help, and we need to give everybody high-quality care. 

This means we have a high volume of work and most of our work takes place through something called the Electronic Health Record, and at this point, there is no real way to interface the data that comes from consumer wearable devices with that Electronic Health Record. So, we really don’t have a good way of integrating any of this into our clinical practice. It’s not that we are absolutely opposed to using this as an adjunct, particularly the ones that have some idea about performance, but we don’t really have a way of getting it in there to make it an easy part of our workflow. Patients will send me screenshots, or they will show me their app in the clinic. 

I think medicine moves slower than consumer-geared technologies for a multitude of reasons, including security issues, but I do think that one day we will get there. And again, we’re not using these as diagnostic tools; we’re using them as an adjunct to our clinical decision-making. So, as long as they are reasonably accurate, and we overall know how they work, I think a lot of doctors would like to adapt them into their practice as long as we have a way of seamlessly integrating that data into our workflow.

Do you think we’re going to see circadian rhythms enter the clinic more in the near future?

Yeah, and what I would hope is that they don’t just enter the sleep clinic, but they enter the wellness and general health area as well. I think a lot of us are doing all of our body systems a big disservice by living in desynchrony with both our central clock and peripheral clocks. 

When my friends and family ask, “What are some of the best things I can do for my sleep and circadian health?” I say “Wake up at the same time every single day.” That’s going to entrain your circadian phase. And hopefully, you’re eating in line with that (and you’re not eating when you’re supposed to be asleep), and when you’re getting light when you wake up. We are all undergoing mild degrees of circadian disruption by varying our wake-up time and getting as much light at night as we are.

Definitely. Especially with screens. I was one of the people who thought my phone screen couldn’t possibly affect my quality of sleep.

Exactly! And I think people are becoming more aware. I mean when you talk about intermittent fasting, that’s kind of a chronotherapeutic measure. It’s so simple, but people get so excited about it. It’s like yeah, don’t eat when your body is biologically prepared to be asleep.

You’re right that it’s incredibly simple, and I think people really respond to small changes that make a big effect on their health and wellness.

And it’s not magical, it’s timing. It’s literally all about timing.

What do you believe the future holds for sleep technology? What are you most excited about?

I’m just hopeful for a day where we change the way clinical evaluation works now, where a  patient might be waiting for me to see them for months and months, and then I see them, give them instructions, send them home with sleep logs so I can see how they’re doing, and tell them to come back to the clinic in 6 months because I’m booked out I can’t see them sooner. 

I want to get to a point where I see them, and at that initial point of care I know what their last 6 months of sleep looked like, and then I can come up with an intervention that’s precise for them and that’s also adaptive based on how their sleep looks in response to intervention. 

Then possibly, when they do go home, we can change that intervention, maybe in an automated way, maybe with me being able to interact with an app, whatever it may be – but instead of writing down instructions and giving people medications, we’re using the mobile application as a prescription to really make patient-specific interventions that are based on wearable data.

So, it’s important to make it less labor-intensive for the patient because then it’s less likely to be done correctly or be done at all.

Exactly, we’re talking about behavior change here. That’s one of the cornerstones of so many diseases we take care of in medicine: they’re due to things that with behavior change could be different, and behavior change is hard. One of the behaviors that we’re really, really good at in current society is working with our devices and our apps. So, I think it’s just a no-brainer as far as delivery goes, I think it’s really time to make this stuff an adjunct and a helper in healthcare.

What have you seen in the clinic in the age of COVID? 

I’ve seen a dichotomy. I mean I don’t think we’ve ever collectively (people my age, middle age, most of my patients) have gone through a stressor like this. So, there are quite a few people who had significant insomnia; there are people that had COVID that had major health disruptions during and following that, including fatigue during the day. Then there are people who actually had marked improvements in their sleep because they can sleep according to their clock, and they have more time due to less commute and so they can extend their sleep a bit. 

There have actually been patients who go off alertness-promoting medications, and are a bit happier with their sleep. There was a great article about a gentleman who had always felt confined to the service industry because he was a night owl. He was always kind of stuck, like a bartender/server, and during COVID (because hours were more flexible with work from home), he was able to go into other industries and have regular hours at the time he selected, and have a more stable work path. Which is what he wanted. You know, we shouldn’t chronotype shame people. Just because you’re biologically late you shouldn’t be at a disadvantage in life, and that’s helped a lot of people’s sleep.

It’s nice to hear some good news come out of the year 2020. That’s all the questions I had lined up, but do you have anything you would like to add?

I think there’s also, what can wearables NOT do. So, we don’t know how accurate the oximetry is yet, we don’t use this as a way to diagnose sleep apnea, I don’t think that sleep staging is something we should rely on. It’s that sleep disordered breathing, is not really something we have not been able to pick up yet, so when people have some episodes of sleep snoring or gasping, feeling sleepy during the day – even if your wearable says you sleep great, that is a limitation and you should still see your doctor.

So, if you feel something isn’t right, it’s best to go in and talk to your doctor.

Exactly, trust your body. The manifestation of diseases is how you feel, not just how your numbers are. 

Categories
Circadian Lighting Personal

Tis the Season: Seasonal Effects and Circadian Rhythms

As today is the shortest day of the year in the Northern Hemisphere (and the longest in the Southern Hemisphere), it seems appropriate to talk about how the seasons change our bodies’ rhythms. Many things change with the seasons, but the main seasonal variation that I will consider here is the variation in day length. 

The seasonal variation in light duration is a big change experienced as you move away from the equator. 

A contour plot of the number of hours of daylight as a function of latitude and day of the year. (Courtesy Wikipedia)

Growing up in Texas, I didn’t really appreciate this variation, but during my graduate school years in Michigan, I experienced it first hand. Personally, the short winter days were a bigger adjustment than the temperature. It felt like anytime I had to drive it was dark and snowing. 

Seasonal changes are known to induce all kinds of physiological changes in our bodies. These include changes in the immune system (Nelson and Weil 2015), physical activity (Shephard and Aoyagi 2009), weight gain (Baranowski et al. 2014), and hormonal changes (Tendler et al., n.d.). Even hair growth changes with the seasons (Shephard and Aoyagi 2009; Randall and Ebling 1991). 

One of the more surprising seasonal cycles is that human reproduction varies seasonally. So called “birth pulses” have been found to occur seasonally within the United States (Huber et al. 2004). Suicide numbers peak in the late spring/early summer. This is also the time of year associated with peaks in aggression and violent acts such as homicide and mass shootings (Geoffroy and Amad 2016). 

Figure taken from Stevenson et al “Disrupted seasonal biology impacts health, food security and ecosystems”, Proceedings of the Royal Society B, Oct 2015. (a) Show the suicide rates in Japan (b) Minor assaults in England and Wales.

Historically, battles and other aggressive behaviors have been shown to peak in this season as well. With all of these seasonal variations, it is natural to ask how the body keeps track of the seasons. Also, what does this have to do with circadian rhythms and the mission at Arcascope? 

First, a bit of background. Our daily rhythms are driven by biological clocks found throughout the body. The most important of these clocks is the central circadian clock located in a region of the hypothalamus called the suprachiasmatic nucleus (SCN). The central clock coordinates and synchronizes the other clocks found throughout the body, and—importantly —the central clock receives light information directly from the eyes. These light signals are the primary mechanism by which our bodies’ internal clocks stay aligned to the outside world. 

It turns out that this central clock is also responsible for maintaining the body’s record of seasonal information (Hannay, Forger, and Booth 2020; Coomans, Ramkisoensing, and Meijer 2015). It is both a daily clock and an annual calendar. This means the core clock has to somehow maintain a longer-term memory of the light it has seen over the past weeks and months. After all, you wouldn’t want to switch into winter mode just because of an especially cloudy afternoon in July. 

The daily 24-hour clock can be found ticking inside each of the individual neurons in the SCN. By averaging across these neurons at the population level (there are around ten thousand of them), you can arrive at a consensus daily time. The seasonal clock seems to work differently: important parts of the seasonal calendar are stored at the population level. This means each individual cell doesn’t know if it is July or January, but if you look at the whole population you can see seasonal changes. In other words, while the daily clock is stored by the consensus or average of the individual clocks, the seasonal information is encoded in the spatial patterns of the clock neurons. 

Interestingly, the seasonal patterns can also feed back on the daily clock and change how it operates (Pittendrigh and Daan 1976). For example, keeping lab animals in summer or winter conditions is known to cause lasting changes to their circadian clocks (the intrinsic period of the clock). These changes can persist for months after they have been moved into a different lighting environment. Another example is that mammals kept in lighting conditions close to long summer days are less light-sensitive than those kept in winter conditions (Pittendrigh and Daan 1976; vanderLeest et al. 2009). One explanation is that the clock needs to be more sensitive to light in the winter for the obvious reason that less light is available (Hannay, Forger, and Booth 2020). 

In modern life, our light exposure patterns do not differ as widely across the seasons due to artificial lighting. In fact, the average light exposure is closer to a perpetual summer (Wehr 2001). This perpetual summer environment has been found to maintain a summer-like state in the melatonin cycle (Wehr 2001). This movement towards perpetual summer has likely suppressed seasonal cycles which are important to maintaining health (Wehr 2001; Stevenson et al. 2015). Mice kept in constant artificial light have been found to have bone deterioration, reduced skeletal muscle function, and disrupted immune function. In humans, it has been shown that natural lighting conditions (camping) leads to a lengthening of the biological night during the winter months (Stothard et al. 2017). 

It is clear that the seasonal variation is important to our health and that modern artificial lighting is disrupting those cycles. On top of that, the long-term memory of light exposures means that these seasonal changes can also affect the operation of the daily clock. At Arcascope our core mathematical models are built to incorporate these seasonal variations— all as part of our goal of helping people maintain healthy daily and seasonal rhythms. 

Citations

Baranowski, Tom, Teresia O’Connor, Craig Johnston, Sheryl Hughes, Jennette Moreno, Tzu-An Chen, Lisa Meltzer, and Janice Baranowski. 2014. “School Year versus Summer Differences in Child Weight Gain: A Narrative Review.” Childhood Obesity  10 (1): 18–24.

Coomans, Claudia P., Ashna Ramkisoensing, and Johanna H. Meijer. 2015. “The Suprachiasmatic Nuclei as a Seasonal Clock.” Frontiers in Neuroendocrinology 37 (April): 29–42.

Geoffroy, Pierre Alexis, and Ali Amad. 2016. “Seasonal Influence on Mass Shootings.” American Journal of Public Health.

Hannay, Kevin M., Daniel B. Forger, and Victoria Booth. 2020. “Seasonality and Light Phase-Resetting in the Mammalian Circadian Rhythm.” Scientific Reports 10 (1): 19506.

Huber, S., M. Fieder, B. Wallner, G. Moser, and W. Arnold. 2004. “Brief Communication: Birth Month Influences Reproductive Performance in Contemporary Women.” Human Reproduction  19 (5): 1081–82.

Nelson, Randy, and Zachary Weil. 2015. “Faculty of 1000 Evaluation for Widespread Seasonal Gene Expression Reveals Annual Differences in Human Immunity and Physiology.” F1000 – Post-Publication Peer Review of the Biomedical Literature. https://doi.org/10.3410/f.725486269.793507034.

Pittendrigh, Colin S., and Serge Daan. 1976. “A Functional Analysis of Circadian Pacemakers in Nocturnal Rodents.” Journal of Comparative Physiology ? A. https://doi.org/10.1007/bf01417860.

Randall, V. A., and F. J. Ebling. 1991. “Seasonal Changes in Human Hair Growth.” The British Journal of Dermatology 124 (2): 146–51.

Shephard, Roy J., and Yukitoshi Aoyagi. 2009. “Seasonal Variations in Physical Activity and Implications for Human Health.” European Journal of Applied Physiology. https://doi.org/10.1007/s00421-009-1127-1.

Stevenson, T. J., M. E. Visser, W. Arnold, P. Barrett, S. Biello, A. Dawson, D. L. Denlinger, et al. 2015. “Disrupted Seasonal Biology Impacts Health, Food Security and Ecosystems.” Proceedings. Biological Sciences / The Royal Society 282 (1817): 20151453.

Stothard, Ellen R., Andrew W. McHill, Christopher M. Depner, Brian R. Birks, Thomas M. Moehlman, Hannah K. Ritchie, Jacob R. Guzzetti, et al. 2017. “Circadian Entrainment to the Natural Light-Dark Cycle across Seasons and the Weekend.” Current Biology: CB 27 (4): 508–13.

Tendler, Avichai, Alon Bar, Netta Mendelsohn-Cohen, Omer Karin, Yael Korem, Lior Maimon, Tomer Milo, et al. n.d. “Human Hormone Seasonality.” https://doi.org/10.1101/2020.02.13.947366.

vanderLeest, Henk Tjebbe, Jos H. T. Rohling, Stephan Michel, and Johanna H. Meijer. 2009. “Phase Shifting Capacity of the Circadian Pacemaker Determined by the SCN Neuronal Network Organization.” PloS One 4 (3): e4976.

Wehr, T. A. 2001. “Photoperiodism in Humans and Other Primates: Evidence and Implications.” Journal of Biological Rhythms 16 (4): 348–64.

Categories
Circadian Sleeping Troubles

Take a Break (From Social Jet Lag)

Why do you go to sleep when you do? 

Sure, there’s a big part of it that’s physical: You go to sleep because you’re sleepy. But you might also stay awake, even when you’re on the verge of collapsing from fatigue because you have work to get done. Or because your neighbor is practicing a percussion solo at 2:00 am. Or because there’s something mildly fun happening on the internet.

It’s like you’re caught in a tug of war, with your body on one side and eighteen different kinds of social pressure on the other. When your body finally triumphs and drags you into sleep, it’s winning out over incoming texts from friends, the snare drum next door, and that interesting passage in the book you’re reading. Team Body can get a boost from a stronger circadian signal for sleep, but it can also be helped along by that responsible part of our brains that tells Team Social Pressure to pack it up and go home, since “We have to get up early tomorrow, folks.”

The absence of this internal chiding is why people tend to stay up later on the weekend than on the weekdays, which shifts their circadian clock’s timekeeping, which makes it so they can’t fall asleep early enough on Sunday, which makes them end up feeling like a right proper Garfield on Monday. This is called social jet lag, and it’s been linked to lots of bad things

But what if we had a very, very long weekend? In other words: how do we sleep when we’re on break? 

I’m going to talk about this through the limited lens of a paper I was an author on in 2017, with collaborators at the University of Chicago. We looked at how people’s Twitter activity patterns changed as a function of where they were living and the time of the year. Tweeting isn’t the greatest proxy for sleep and wake, but we can at least conclude that if someone is posting a tweet, they’re probably—though not necessarily—awake.

You can make plots like the below, where the blue lines show the (normalized) amount of tweets at any point in time over the course of the day, on weekdays (dark blue) versus weekends (light blue). 

When the lines are low, less tweets are happening then. When the lines are high, more tweets. In the plot on the left that shows February tweeting, you can see a huge difference between weekday and weekend tweeting. In the plot on the right, for August, the minimum points for tweeting (the troughs) are nearly the same.

I remember seeing this and thinking, “Ah-ha! Seasonality effects! Human behavior is changing because the sun is changing over the year!” This, I thought, would be very interesting to report on. 

Then somebody on the team (one of my brilliant co-authors), wondered if it wasn’t just that people were more likely to be on vacation in August than in February. 

Reader, it was totally that.

Or, at the very least, we found some pretty compelling data to suggest that the reason why “Twitter social jet lag”— the difference between the trough in tweeting on weekends versus the weekdays— was higher in February than in August was not because of the sun being different in those two months, but people’s social responsibilities being different in those two months. 

Just look at the timing of the weekday tweeting trough versus the week of the year (red line), alongside the timing of big K-12 holidays (yellow) in Orange County, FL:

Sure looks to me like every time the kids go on break, people’s tweeting activity shifts later in the day. (You see this in other counties, too).

It’s true that tweeting in 2017 might have been disproportionately done by younger people. But this still means that, according to this proxy for sleep and wake, their social jet lag was decreased. They didn’t have to get up early for school or work, so they didn’t, and there wasn’t much of a difference between their weekdays and weekends. 

Which is a good thing! Don’t get me wrong: society is still set up in a way that punishes night owls more than early birds. But having your sleep be more consistent, and not jaggedly interrupted by the weekend, is healthy. 

This December, as we cruise towards that glorious week between Christmas and New Year’s, the sleep of those of us on vacation time will probably shift later, like we’re in one big, endless weekend. Wednesday will look like Saturday. Sunday night and Monday morning will be no big deal. 

The problem comes when we go back. Because if Twitter activity patterns are to be believed, the coming months are some of the worst in terms of “jet lagging” ourselves on the weekend.

So with the holidays coming up, take the time to rest and sleep in a nice, consistent way. Then keep it going into January. This will mean quashing down the parts of you that push for staying up late on Friday and Saturday as much as you can. But it will also mean that one of the best things about the way we seem to sleep on break will carry forward with you into the new year: better weekday-weekend sleep regularity. 

Oh, and by the way: this sleep regularity? In some ways, it might even be more important to your health than sleep duration. But more on that after the break. 

Categories
Circadian Personal Sleep Meme Review

We Rate Sleep Memes

Here we see Squidward staying up and reading instead of going to sleep. Squidward himself might smugly point out that he’s reading a book, not looking at a light-emitting screen, and use that as an excuse to feel superior. If so, he would be tragically mistaken. There are clearly lights on in the room that he’s using to read while staying up late, and that light will have an effect on his clock much in the same way light from a screen would. After all, most homes are bright enough in the evening to significantly mess up sleep-related processes, like melatonin production. Though Squidward would never accept it, his efforts to prevent circadian disruption pale in comparison to those of his neighbor Patrick, who blocks light by being a starfish who lives under a rock. 

Originality: 3 out of 5. Not being able to put your phone down is a classic meme topic. 

Quality: 4 out of 5. Slight cognitive dissonance caused by the “scrolling through social media” text coupled with the image of him reading a book, but it gave us a chance to talk about how room light exposure matters for circadian rhythms, which is what we’re all here for. 


Let us start by noting that Homer’s perception of his sleep here may be skewed: many people with insomnia overestimate how long it takes them to fall asleep, and underestimate how much sleep they actually get. It may be that a more accurate version of this meme would be “me all night vs me four hours before my alarm goes off”– which is still, to be perfectly clear, a miserable experience. It’s miserable even if you’re objectively getting more than 6.5 hours of sleep per night but perceiving that you’re not sleeping much at all (also known as “paradoxical insomnia”). We love targeting sleep improvements through light exposure over here, but if you’re relating hard to this meme, you’ll probably want to get yourself some cognitive behavioral therapy

Originality: 3/5. This, too, is a pretty typical sleep meme topic.

Quality: ⅘. He looks very cozy at the end there. 


Oh, Leo. Leo, no. This is a terrible idea.

For starters, we know what happens to people who get four hours of sleep a night. First, they have more and more “vigilance lapses” with every passing day (4 hours of sleep a night = circles in the below, black squares = no sleep, white squares = 6 hours, diamonds = 8 hours). 

A vigilance lapse means that something popped up on a screen in front of you for half a second and you didn’t even register it. This is bad if you are, for instance, driving a car. 

People on four hours of sleep a night also fail to get better at subtraction and addition tasks, despite days of practice (see: circles staying flat in the below):

And yes, caffeine can counteract “getting worse and worse at things” to an extent, but so can naps. As the authors of a recent review on fatigue and caffeine write, “It is important for caffeine consumers to understand that caffeine at any dose is not a chemical substitute for adequate healthy sleep.” 

Originality: 4.5/5. Nice shout out to shift workers.  

Quality: 2.5/5. Inscrutable indenting decisions. Objectively bad sleep practice. 

Categories
Circadian Lighting Personal

This Thanksgiving, Get Outdoors

Here’s a fun fact: You probably get way less light exposure during a normal work day than you would if you were out camping.

“Sure,” you say. “That’s no surprise. At home, I have walls around me to block the sun. If I’m camping, I presumably have fewer walls.”

“You don’t understand,” I say, leaning in. “You get way, way less light exposure.”

I’m basing this off a famous circadian experiment from Ken Wright’s group at the University of Colorado Boulder, in which they compared the light people get in modern electrical lighting environments with the natural light they get while camping. 

It’s not a 1x or 2x difference when you go from modern light exposure to camping light exposure. It’s a 13x difference

Thirteen times more light exposure during the day! And this in the winter! It’s nuts. 

Imagine turning your current daily light exposure down by a factor of 13, or to 8% of its current brightness. Two things would probably be true. First, it would be hard to see, so you’d bump into things. Second, and most important from a circadian perspective, it would be hard for your brain to tell the difference between day and night. 

After all, the signal telling your brain that it’s day (light) would be just a tiny fraction of what it was before. It’d be like turning a faucet down to just a thin drizzle. You can tell it’s on if you look for it, but it’s an easy thing to miss. 

In a sense, we’ve already done this with the shift from natural lighting to indoor, artificial lighting. We’ve given up the firehose of light that is sunlight exposure in favor of a much muted signal from our indoor lights and devices. 

If you look at the lighting figure above from Stothard et al., it’s ridiculously easy to see where day starts and stops in the camping conditions (black line). But the picture is muddled for modern electric light (gray line): Day seems to start fairly clearly, but where does it end? There’s this blunted peak in light exposure during the day, and a long, ambiguous tail of light exposure stretching out into the night hours. There’s not really a clear day/night divide. 

This matters for our health. There’s a notion in circadian rhythms science of your circadian “amplitude.” Roughly, you can think of amplitude as a measure of how confident your body’s clock is about the time it thinks it is. Give your circadian clock a clear day/night signal, and this will boost the amplitude. Keep it on a constantly changing, dim-light-round-the-clock kind of schedule and the amplitude goes down. 

In other blog posts, I’ve talked about your phase response curve, which tells you which direction (earlier, later) light will push you when you get exposed to it. But you can also think of the amplitude response curve, which tells you whether your amplitude will go up or down if you get light at a certain time. Generally speaking, the amplitude response curves in our models tell you to go outside right smack in the middle of the day if you want to boost your amplitude as efficiently as possible. 

So this Thanksgiving, get some outdoor light. Sure, yeah, get some exercise while you’re out there if you want. But simply being outside and in the light is a good thing: It’s building stronger, more robust rhythms in your brain. And if you happen to fall asleep hard after eating a big meal– well, part of it might be that your circadian clock’s a little more confident that day is over and it’s time to snooze. 

…part of it. 

Categories
Circadian Lighting Personal

inTRO to ipRGCs

Rods, cones, and…ipRGCs?

For almost a century and a half, it was thought that the mammalian retina had just two types of photoreceptors: rods and cones. That assumption was not proven to be false until studies in the late 1990s proved the existence of a third kind of mammalian photoreceptor that differed greatly from rods and cones. These new types of photoreceptors were retinal ganglion cells (RGCs) that were intrinsically photosensitive (ipRGCs)— or in other words, naturally sensitive to light.

Though the official evidence to determine that ipRGCs actually existed did not come until much later, this third class of photoreceptor had already been hypothesized in 1927, nearly seven decades earlier, by a graduate student named Clyde Keeler. During one of his studies, he examined the behavior of mice that lacked nearly all rod and cone function as a result of severe retinal degradation, which left them functionally blind. Keeler noticed that despite the lack of rods and cones, the mice still had a very strong and significant pupillary constriction in response to light, and he determined that this response must have been the result of some third photoreceptor in the retina. The lack of concrete evidence for a whole new photoreceptor at the time resulted in this pupillary response being explained away by other scientists. However, in 1999, Russell Foster and his team would revisit Keeler’s work armed with a new host of tools.

Foster et al. worked with mice, much like Keeler did, but in their case, the mice being observed were genetically engineered to not have any rods or cones. Yet regardless of their missing rods and cones, the rats still displayed strong pupillary light reflexes and were even able to shift their circadian rhythms with shifting light exposure schedules. With these studies complete, the presence of a third photoreceptor was almost confirmed, but some still weren’t convinced because nobody had found another light-sensitive molecule (opsin) in the mammalian retina yet.  

The discovery of melanopsin in the photosensitive skin cells of frogs occurred in 1998, and in the following four years studies determined that the very same opsin was being expressed in a small percent of RGCs in both mouse and human retinas. This discovery allowed scientists to easily mark ipRGCs and confirm their existence, which finally put to rest the debate of whether or not there was a third class of photoreceptor.

So they exist, but what do they do?

IpRGCs differ greatly from rods and cones when it comes to how they work. Their main function in the body is to signal the intensity of ambient light levels (irradiance) to the brain. These signals are largely used for non-image-forming visual reflexes that are subconscious, such as pupillary constriction, neuroendocrine regulation, and synchronizing daily circadian physiological rhythms to environmental light. This means that the way ipRGCs respond to light by themselves is also quite different from rods and cones.

As mentioned before, these photoreceptors use melanopsin as their photopigment. and that makes them more responsive to light at around 480nm (blue light). In the graph below, you can see that this wavelength is significantly different from the best wavelengths for stimulating rods and cones (panel b).

From: https://webvision.med.utah.edu/book/part-ii-anatomy-and-physiology-of-the-retina/melanopsin-expressing-intrinsically-photosensitive-retinal-ganglion-cells/

Although ipRGCs function as photoreceptors themselves, it was found that they additionally receive synaptic input from the circuits of rods and cones. This means that ipRGCs have both an intrinsic light response coming from melanopsin and an extrinsic one that is mediated by synaptic input from rods and cones. The light response caused by melanopsin is markedly different from that of rods and cones: ipRGCs have both an intrinsic and sluggish light response as well as an extrinsic, rod/cone driven, rapid photoresponse. There is an ongoing debate about the relative significance of this extrinsic synaptic input and the role rods and cones play in determining our circadian rhythms.

A recent case study:

In a recent research article by Mouland et al., their team assessed whether the effective light intensity registered by melanopsin (blue light ~480nm) was a more important determinant of circadian impacts than that of cones under realistic contrast scenarios. The ability to determine melanopsin’s contribution to circadian light responses comes from the evolution of a color science technique which is referred to with multiple names, such as receptor silent substitution or metamerism in colorimetry. Metamerism occurs when two colors appear to match under a specific lighting condition but have different underlying spectra. 

From: https://en.wikipedia.org/wiki/Metamerism_(color)

This technique allows for the stimulation of specific photoreceptor classes, like ipRGCs. Mouland and colleagues quantified the circadian impacts of different photoreceptors by recording electrophysiological activity from the suprachiasmatic nucleus (SCN) of anaesthetised mice while they were presented with movies. The movies were either high or low contrast and had varying irradiances specialized for the distinct photoreceptor classes. 

During the experiment, the energy response recorded from the SCN closely tracked with melanopsin-driven signaling across all conditions. In general, steps in melanopic irradiance were determined to be the most significant factor accounting for light-induced changes in SCN activity. The only cone-directed lighting patterns with significant impacts on SCN activity were low contrast movie conditions. Basically, this study suggests that cones do have an impact on the circadian signal going to the SCN in some conditions, but the influence of melanopsin on the circadian signal is far more consistent.

This blog post was written by Arcascope’s intern, Ali Abdalla. Thanks, Ali!

This post used Webvision as a major resource. Thanks to Dustin Graham and Kwoon Wong for the excellent review.

Categories
Circadian Lighting Personal Sleeping Troubles

No, we shouldn’t make DST Permanent

I recently got some blackout curtains for my bedroom. This was pretty long overdue: about thirty feet from my bedroom window is a cheerfully bright, energy-efficient street lamp, which—while great when I’m taking the dog out for a nighttime stroll—is the photic equivalent of somebody standing in my azaleas and playing “Seventy-Six Trombones” while I’m trying to sleep. 

I’ve definitely started sleeping longer since I’ve gotten them. But I’ve also noticed that they’ve made it so I need to be even more careful about my other sources of light at night. The reason? They don’t just block my light at night. They also block light in the morning.

I’m thinking about this because it’s almost the end of daylight savings time, and, once again, there’s talk of making it permanent. As a quick guide: Daylight savings time (DST) is the one where the clocks move forward (so it’s lighter at night), while standard time is the one where the clock moves back (darker at night). The “Sunshine Protection Act”, introduced by Florida senator Marco Rubio, encourages states to observe a permanent version of DST, with the argument being that lots of good things could come out of just chilling it with the time change. 

Permanent daylight savings time means not having to change the clocks, and not having to experience that gnarly “lose an hour” in the Spring. It means no confusion about how many hours offset we are from the time in the U.K. and no struggling to remember if you should say EDT or EST when you’re trying to coordinate a Zoom meeting across time zones. As a programmer, I’m generally in favor of anything that makes the totally miserable experience of interacting with dates and times in code even marginally easier. 

But it also means—and I’m talking about permanent daylight savings time here—lots and lots of dark in the mornings. 

This is bad. It’s bad because light at night is fundamentally different from light in the mornings, because our bodies are fundamentally different at night than they are in the mornings.

Note: This picture does not apply if you’re a shift worker, a recent traveler, or otherwise circadianly weird.

Light in the morning does a couple things, but one of the most important ones is that it “advances” our circadian rhythms. It tells our internal clock that night is over and it’s time to get a move on. It makes it easier to fall asleep at night. 

And if you get a lot of light in the morning, it eventually advances you to the point where… it stops advancing you. You enter the part of your daily rhythm where light delays your clock. A sort-of “slow down, what’s the rush” period of your internal rhythm that starts in the mid-afternoon for most people and continues into the early morning.

More light in the morning: The permanent standard time solution.

And that slowdown period is the problem. Because while light in the morning is hitting you in the advance region, which you eventually get advanced out of, light at night is hitting you in the delay region, which is like a temporal sand trap. When you get light exposure in the delay region, your clock gets slowed down, which means you spend more time in the delay region. Which means you don’t feel tired as quickly, which means you get more light, which means you spend even more time in the delay region. It’s a feedback loop that spins out of control. It might be the reason that night owls exist

Permanent DST (gasps in circadian horror)

So if we adopt permanent DST, we’re adopting a schedule where we get more light during the hours most people call night, and much less light in the hours we consider morning. We’re setting ourselves up to fall into the delay region sand trap: More light in the night, making us stay up later and get delayed, and far less light in the AM hours to counteract it. 

This is what tanked permanent DST the first time we tried it. I’m not sure why this doesn’t always get brought up as the very first point against permanent DST, but we’ve totally done it before. In 1973, anywhere from 57-73% of people supported staying on DST during the winter. So they did it, in January of 1974. By the time February and March rolled around, only 19-30% of people still thought it was a good idea, while 43% said it was actively bad. 

What changed? People experienced what happens to your body when you have to kick off your day in the dark of night. They drove to work and caught the bus to school, while the sun waited to rise until 8:00 am. They didn’t like it, and rolled the decision back before the next winter came around. 

You might say, “well, time is a fake idea. Who says you have to start your day before 8:00 am?” This is a fair point. We could, societally, shift the normal times we do things to match whatever schedule we wanted. In China, where the entire country is on the same time zone, places like Kashgar (in the far west) have shifted their normal operating hours to reflect the fact that the sun might not come up until 10 am. 

But it’s a lot tougher to change social standards of when school and work “should” start in every town in the country than it is to pass a bill changing the time that appears on your phone. Which is why we shouldn’t do it: Permanent DST will put us on schedule where our traditional social standards for when things should happen are at odds with our biology, sabotaging our sleep and circadian health.


If we want to stop the whiplash of changing the clocks twice a year, why not do permanent standard time? I’m in favor of this. It reduces confusion the same way permanent DST does, but without the corresponding damage to our internal rhythms. Sure, it might mean that 9:00 pm is dark, even in the summer. But darkness at the right times is a healthy thing. And from a safety perspective, there are lots of street lamps and other sources of light at night these days that are very good at their jobs. 

Which brings it back to me and my blinds: I’ve needed to be more careful about my other sources of light at night lately because my blackout curtains mean I don’t get woken up by the sun. That’s not a big problem: I can wake up in the dark and yank them open myself, like one of the townsfolk in the first song in Beauty and the Beast

But if I get too much light at night from non-streetlamp sources, like watching Succession on my computer or looking at Succession memes on my phone, my ability to wake up in the dark in the morning is going to be less reliable, jeopardizing my exposure to that vital morning light. And I’m lucky that there’s even morning light to get: with permanent DST, I could be hopping on my first calls of the day while the sky is still black outside. 

My point is that social pressures already make it hard for us to get the darkness we need at night (let’s face it, screens are fun) and the light we need in the morning. We shouldn’t make it harder for ourselves with a change to a system that’s already failed once. Permanent daylight savings time is a no-go. Permanent standard time? Call me. 

Categories
Circadian Personal Technology

Yesterday’s Weather

I love my Apple Watch. The ability to track my exercise, heart rate, activity levels, and sleep has enabled a real awareness of how my physical and mental health changes over time. The ability to track personal health data over long time periods outside of laboratories is one of the most exciting developments of the last decade. I believe this data will usher in a new era of personalized, precision health which just wasn’t possible in the past. At Arcascope, we are at the forefront of developing algorithms to turn the data collected by wearable devices into insights that improve people’s lives. 

With that being said, the current state of things just isn’t all that satisfying when you think about what’s being left on the table. So much of the data being collected is uninterpretable. Knowing my current heart rate is cool, but what can I do with that information? The part of this that bothers me the most is that so much of this data is focused on the past. 

Here is a screenshot from Apple Health showing my sleep over the last month. You can see that I had some wake periods at 3 am at the beginning of the month. But how does this information really help me? 

Sleep tracking in particular reminds me of a weather app that can only tell you yesterday’s weather. Clearly, a weather prediction service that could only tell you the weather from 24 hours ago wouldn’t do well against the Doppler radar. It is useful to be able to say exactly how hot it was yesterday, and interesting to know how that compares to years past, but I really want to know if I should bring an umbrella with me when I leave the house. 

I can tell that I didn’t sleep well last night from the fact that I am feeling tired. Having a device to quantify exactly how poorly I slept can be useful for tracking long-term trends, but it isn’t all that useful on a day-to-day basis. 

Another snapshot from my Apple Health data. Doesn’t this remind you of a weather app pointing out how this weather’s month compares to historical trends? What about today? Or how about tomorrow?

Okay, enough of the weather prediction analogy. I’ve already pushed that analogy further than I should. First, unlike the weather, we actually have control over our behavior, and what we are doing now will change the forecast for our physiology tomorrow. Also, these variables are much more predictable than weather. 

The technology we have developed at Arcascope can answer questions like: 

  • What separates the days where I am at my best, from the ones where I am struggling? 
  • How can I alter my behavior now so that I will sleep better tonight?
  • When is it best for me to stop drinking coffee for the day? 
  • When will it be best for me to study, exercise, eat and relax? 
  • When is the best time to take my medication to minimize side effects? 
  • When should I avoid high stakes activities because my chances of making a mistake are highest? 

We believe this is the future of personalized health tracking. We also think it’s a heck of a lot more exciting than looking back at yesterday. 

Categories
Circadian Personal

Let’s talk about Time-Restricted Eating

I have always been a good eater.

Back when I was in college—waking up at 4:50 am for crew practice, staying up until 1:00 am working on problem sets, and sleeping in until noon on my days off—I could eat pretty much any food in any amount at any time of the day. And I mean anything, anytime. Think: bootleg s’mores made out of saltine crackers and ice cream toppings. Cooked in the microwave. At 6:45 in the morning. 

Something changed in graduate school, when I stopped having wildly irregular sleep schedules and got my circadian act together. I just… didn’t feel hungry after a certain point in the evening. And if I tried to eat something very late in the day—say, a midnight snack— it actively made me feel… kinda bleh. 

My philosophy around food has always been to eat when you’re hungry. But once I was on a regular schedule, I stopped feeling the constant, slow-burning hunger I’d had back when I was up at all hours. I still felt hungry, but only at certain times of the day. The rest of the time I wouldn’t really feel hungry at all. You might say that my eating and hunger patterns became more strongly rhythmic.

Enter circadian rhythms. It makes sense to think that our bodies might be more prepared to handle food at some times (like when we’re awake), rather than others (like when we’re supposed to be asleep). And the same way light at night confuses and disrupts the central clock in our brain, so too could food around the clock confuse and disrupt the peripheral oscillators in our organs. Buying all this, how might you avoid this disruption? Eat what you want, but only over a portion of the day. 

This is time-restricted eating, or TRE: the idea of keeping all your eating to the same window of time every day. Usually this window is 8-10 hours long. So if you get up and start eating at 8:00 am, you might restrict your food intake to ten hours a day and stop meals after 6:00 pm. Or you might hold off on eating until 11:00 am, in which case you’d wrap up food for the day around 7 – 9:00 pm. You might only do this for five days of the week, or you might do it every day. Regardless, this isn’t about actively trying to cut calories. It’s not about how much you eat, it’s when. 

TRE came out of the work of Dr. Satchin Panda, a professor at The Salk Institute and author of The Circadian Code.

His group found that simply restricting eating windows led participants in their studies to feel more energetic, sleep better, and show improvements in cholesterol and blood sugar. He’s even got a research app you can download to participate in his group’s studies at myCircadianClock.org (note: we’re not affiliated with this project, we’re just fans). 

Not everyone can manage TRE with their job (night shift workers, for one, often have to fuel whenever they can), and people with underlying health conditions should talk to doctors before giving it a try. But as someone who fell into a time-restricted eating schedule somewhat by accident, I have no plans of quitting anytime soon. I’ve lost a fair amount of weight since my undergraduate days, and it’s not because ever stopped eating s’moretines. I’ve just gotten to the point where my body has a much clearer signal than it used to for when it wants food and when it doesn’t. 

So take a look at Dr. Panda’s website, or book, and consider if TRE makes sense to try out. After all, the timing might be right for you. 

Categories
Circadian Personal Sleeping Troubles

Measuring Sleep Regularity

What is sleep regularity and why is it important?

Sleep regularity is a gauge of how consistent a person’s sleep patterns are, based on the day-to-day variability in their sleep–wake times. In general, having poorer sleep regularity, or irregular sleep patterns, has been shown to lead to many adverse outcomes in metabolism, mental health, and cognitive performance. Low sleep regularity has even been linked to increased inflammation. In order to avoid these and other complications, you want to increase your sleep regularity by aiming to get into bed at the same time every night.

How can we score sleep regularity?

There are at least five different metrics that can be used to quantify sleep regularity, each capturing different aspects of it and useful in its own way. The five measures of sleep regularity that we’ll look at in this blog post are listed below:

Traditional/Overall Metrics:

  • Individual Standard Deviation (StDev)
  • Interdaily Stability (IS)
  • Social Jet Lag (SJL)

Newer Metrics:

  • Composite Phase Deviation (CPD)
  • Sleep Regularity Index (SRI)

Traditionally, the most common overall metrics that have been used to assess sleep regularity are quantified by measuring sleep deviations in sleep patterns from an individual’s average. Examples of overall metrics are StDev and IS, both of which compare sleep from each day to an average sleep–wake pattern, and SJL, a metric that compares two average sleep patterns (workdays and free days).

StDev: lower is more regular / StDev⬇ = Sleep regularity⬆

This score is just the standard deviation of your sleep metric of choice, like sleep onset, sleep offset, or sleep midpoint. The standard deviation captures the variation of a quantity from its mean. 

IS: higher is more regular / IS⬆ = Sleep regularity⬆

This metric uses sleep-wake data (can also use rest-activity data) over a period of days to measure the stability of a person’s sleep-wake rhythms. It does this by comparing the pattern of daily sleep activity to the average pattern across many days. 

SJL: lower is more regular / SJL⬇ = Sleep regularity⬆

Social jet lag is a metric that quantifies the mismatch in the average mid-sleep timing between workdays and free days. Negative SJL values represent earlier mid-sleep timing on weekends than weekdays while positive values indicate the opposite.

Two newer measures of sleep regularity are CPD and SRI. These two fall under the category of consecutive metrics, which means they measure variability in sleep–wake patterns between consecutive days. The circadian system makes adjustments daily, and consecutive metrics were developed in order to utilize day-to-day information and more accurately predict circadian disruptions associated with poor sleep regularity.

CPD: Lower is more regular /  CPD⬇ = Sleep regularity⬆

Composite phase deviation is a metric that was created with shift workers in mind. CPD quantifies circadian disruption where sleep is both irregular (rotating shifts) and mistimed (sleeping in daytime). This metric uses an individual’s chronotype to determine optimal timing of sleep. The chronotype then helps to quantify how “mistimed” they are. The regularity aspect is calculated using the difference between mid-sleep timing from one day to that of the prior day. In order for CPD to be derived it requires data that has one main sleep session per day or some other daily sleep variable, like sleep duration.

SRI: higher is more regular /  SRI⬆ = Sleep regularity⬆

The sleep regularity index is a measure based on binary sleep-wake time series. It measures the similarity of a person’s sleep-wake pattern from one day to the next. The scale for this metric ranges from 0 (random) – 100 (perfectly regular) and it represents the percentage probability that an individual will be in the same sleep/wake state at any two time points. It’s important to note that this metric does not account for total sleep time so a person that (hypothetically) sleeps 0% of the time will still be able to get an SRI value of 100.

So I’m regular, that means I’m healthy right?

Well, not quite. Depending on the kind of variability you have in your sleep patterns and the method used to record your sleep, different metrics may tell you very different stories regarding your sleep regularity. Context is very important when making a decision about which sleep regularity metric to use. 

Just think about what would happen if you increased the variability in your work week sleep timing, but maintained a consistent average. Your SJL score would stay the same, while your other metrics would likely shift to indicate greater variability. The ordering of days also matters. In Fischer et al. they shuffle days around to show how consecutive metrics can give you different stories on regularity than overall metrics do.  

In order to properly assess sleep regularity for yourself or your patients, it is necessary to understand the little things that go into calculating each of these sleep metrics. A variety of unknowns, such as the type of data being gathered or the length of the data set, can cause these metrics to disagree with each other. The good news is that you’ve got lots of options to choose from. 

This blog post is heavily based on “Measuring sleep regularity: Theoretical properties and practical usage of existing metrics” by Fischer et al. The authors didn’t have anything to do with the making of this post, but we want to thank them for writing an inspiring paper. 

This post was written by Arcascope’s intern, Ali Abdalla. Thanks, Ali!