Hi, welcome back.

As you know, I'm Doctor Cathy Goldstein and I have a very

special colleague right now with me, this is Doctor Olivia Walsh.

So Olivia, if you could just start by telling us your background and

how you became interested in sleep.

>> Yeah, absolutely, so my training is in Mathematics.

I did my undergraduate work in Mathematics at the College of William and Mary.

I came to Michigan, I knew I wanted to do applied math,

I started working with a professor here, Danny Forger,

who studies the Mathematics of sleep and circadian rhythms.

And through working with him, I started making models of circadian rhythms and

apps to communicate these models to the world.

>> Is there anything personally that drew you to this kind of work?

>> Honestly yeah, as an undergraduate I did not sleep enough, it was very bad.

And as a result, I kind of don't remember what it was like in college.

I completely did not form new memories, [LAUGH], for a lot of that time.

And as a result coming to grad school, I first of all,

I was like I gotta start sleeping.

And secondly, I was really interested in understanding more about

something that's so important.

But that we often treat it like not only is it not important but

at it's macho to not get enough sleep.

>> Definitely, huge problem right now.

For learners, can you review a little bit about what circadian rhythms are?

>> Yeah absolutely, so

a circadian rhythm is anything in your body that repeats itself once a day.

That's a lot of things.

So okay yeah, you ca usually sleep once a day,

but you also have peaks in performance in so many different systems in your body.

So your grip strength has a circadian rhythm, your metabolism has a circadian

rhythm, your immune response had a circadian rhythm.

If you were in a bunker and had no access to light,

your clock, the thing controlling all of these things repeating itself,

would do that at a period of around 24.2 hours.

It wouldn't be a normal 24 hour day, but

we're kept in sync with our environment by light.

Light is the main input to your circadian clock.

>> Olivia, so can you tell me exactly how light affects the circadian system?

>> We didn't know for a long time, we knew that it wasn't the rods and cones.

So the traditional visual pathway is light comes to your eye,

it's picked up by rod and cone photo pigments.

Cones are what see color, rods are more light, dark,

they transmit that information through the retinal ganglion cells that talk to

the visual parts of the brain.

But in the early parts of the 1900's, people had noticed that blind mice,

mice that could not see still had circadian rhythms.

So these mice were missing rods and cones, but

somehow light information was still getting to their brain.

It was a mystery for a long time.

The early math models of the circadian clock didn't know what they were,

so they put in placeholder terms.

But in the early 2000s we figured it out.

There's a photo pigment in your eye called melanopsin, it was actually first

discovered in the skin of frogs, but it's also in your human retina.

The light coming to your eye hits melanopsin that's intrinsically

photosensitive retinal ganglion cells.

Those IPRGCs are what send the message from your eye to

the suprachiasmatic nucleus, the master clock of the body,

where controlling rhythms is the number one thing it does.

>> Very cool, so

if you're somebody that's being exposed to an abnormal light dark cycle.

For example, you're a night shift worker, or

you travel to another country and you get jet lag.

What happens to the clock then?

>> It gets completely confused.

Like I said, light is what's keeping us in sync with our home environment.

So if you get late at a weird time, the clock doesn't know what to think.

It might be expecting darkness, a burst of light comes in and it sends a signal that

updates the phase of your clock, the internal time of your body.

And if you adopt a new light schedule like for instance, if you cross time zones and

then just say okay I'm in Tokyo now, I'm gonna follow my normal schedule.

But in Tokyo you will adjust, it's this process called entrainment, but

is not necessarily the fastest way to adjust.

If you get late at the right times,

you can adjust yourself to a new time zone, faster.

>> And how did you guys use math to help speed up that process?

>> So the clock is a really nice system to model with math.

A lot of biology is really hard to do math on because it's so complicated.

But the clock is a relatively clean system, and

we know the most important input is light.

So over the course of decades now, people have been developing and

refining math models, that take as the input, light.

And then, they process it, and get, as an output, internal time.

And so, the internal time of a person

can be approximated if we knew the recent light history.

And this is based on lots and lots,

of experiments where people are in dim light or constant light conditions,

and they're getting lights flashed on them, they're spitting into tubes.

But through that, we can come up with math models.

And then once we have a math model,

we can do a kind of mathematics called optimal control theory.

And this is the same kind of math you would use if you were asking okay,

I want to have a ball and design for the best slide for

getting the ball from here to here as quickly as possible.

Most of the applications of control theory have been for physics, but

we took it and applied it to biology, specifically,

this really clean model of the biological clock.

>> That is unbelievable.

So we talked about this in kind of reference to shift workers and people

travelling across the world, but what about what all of us do on a weekly basis?

So I know that most people, come the weekend,

they push themselves to stay up later, and then they sleep in two to three hours.

Can that have relevance in shifting the clock?

>> Absolutely that's called social jet lag.

It's something that was coined by a researcher named Till Roenneberg.

The idea is you're basically crossing time zones if you wake up one time for

work and then you wake up three hours later on the weekend on your free day.

It's been correlated to a bunch of ill health effects like risk of obesity.

And the way to think about it, or how I think about it,

is imagine you're on a swing, you've got really nice amplitude going.

You are doing awesome on this swing.

This crossing of time zones, it's almost like somebody pushing you

at a point in that swing that isn't the best for your amplitude.

I don't know if you've ever had like a jerk on the playground,

who pushes you at the wrong time.

You lose amplitude on the swing because you're not able to get that full

oscillation.

And when you are changing time zones every week, it's kind of like you're on a swing

and somebody's just shoving you and you can't get that really strong rhythm going.

>> So it sounds like a lot of people are really messing up their clocks and that

this is just a widespread problem even if you're not an international traveler or

you're not a shift worker.

So can you tell me a little bit about the app that you developed

here at University of Michigan and train, and how that can help?

>> Yeah absolutely, so we were doing this research into the circadian clock,

the best presentation of light to shift a person in time zone A,

to time zone B as quickly as possible.

And we got a bunch of schedules that people could use to cross time zones.

And we didn't wanna just publish them in an academic paper and

have them be used by only us.

So I made an app where people could enter where they were starting from,

and where they were going to and also their normal lighting habits.

Cuz somebody who normally wakes up at four am has a very different circadian

oscillation over the course of the day than somebody who wakes up at 11 am.

So with those pieces of information,

we relaid the schedules, put it out there in an app.

This was actually my first ever app that I made, and it got a lot of attention.

And I think it's because people are starting to realize that the circadian

clock affects so many things, and that jet lag is

a major problem that affects everybody, not just travelers.

So the app was released, we gave people who wanted to,

the chance to opt in to submit their data back to us.

A huge number of people did where we're in to 10,000 now.

Which is great, because it's not just download numbers,

that's people who chose to send their data back to us.

And from this we can get a snapshot of how people sleep the world around.

>> That's fantastic, and if our viewers want more information about that app?

>> They can check out in train.org.

>> Perfect, so

if you had to tell everyone one thing to promote health of your internal clock,

which subsequently affects your sleep and your alertness, what would it be?

>> I would say keep a regular schedule.

Not just a weekend versus weekday, I would say over the course of the week,

as much as you can, try and keep a regular light dark schedule.

And I believe this because of the science, but I was also a subject

in a circadian study, where for five months I had to keep a regular schedule.

I had to go to bed at the same time every night and

wake up the same time every morning.

And I didn't have to fall asleep right away, it was just a matter of

controlling my light so that after 11}30 I was not getting light.

And I cannot tell you how healthy I was.

Those were the five months of maximum health in my life, and

ever since then its just been downhill, I've gonna get back to that.

Seriously, I know it's hard, but as regular schedule as you can,

get I think that's really great.

>> Well, I would definitely agree with that.

I thank you so much, Olivia, for this fascinating discussion

about the effects of the clock and how math can help us understand it.

>> Thank you for having me.

Regularity of Schedule: An Interview with Dr. Olivia Walch

Sleep Deprivation: Habits, Solutions, and Strategies

Meet the Instructors