Translator: Theresa Ranft Reviewer: Denise RQ
In case you didn't know, 2015 is the International Year of Light.
So, I thought I'd tell you just a little bit
about the impact of light on our health.
My lab uses fruit flies to study sleep and wake patterns,
but what I want to talk today
is primarily light and its impact on health.
So, of course, we live on this planet
that spins around its axis as it's orbiting the Sun.
As a consequence of that, one of the basic facts of life on Earth
is that you're exposed to light-dark cycles every single day.
Here you see the side of the Earth that's facing the Sun, is light,
and the other one is dark,
and actually, I think we have so much light here
that the dark side is kind of washed-out.
But if the light was a little bit lower,
you could see that there are lights all over the places on Earth,
at least where there's solid ground, just not above water.
And that's maybe a little bit more clear from this picture
which is a composite Google image of Earth from above, at night,
and I think that this is a really stunning image.
It's stunningly beautiful, but it's also stunning to think
about the amount of light that we're enveloping the Earth on,
and, at the time of day when,
for pretty much all of our evolutionary history,
the Earth has been dark.
There's this funny story that I don't know if it's true,
but I like it, I think it's a good story,
where in 1994, in LA, police started getting reports
of people seeing a strange white cloud in the sky,
and they didn't know what this was.
They wondered if they should be worried.
It turned out LA had just suffered a major earthquake
which resulted in citywide blackouts.
So, many people for the first time in many years,
or perhaps the first time in their lives, had an unobstructed view of the night sky.
In fact, what they were seeing was not a trail from some alien spaceship,
but it was a glimpse of our own home galaxy, the Milky Way.
This may sound quite incredible to you until I show you this next picture.
Here's a picture that this guy, Todd Carlson, from Canada,
took of his house, a fairly typical-looking house,
a typical-looking sky,
at least for those of us living in Boston, or surrounding areas.
You can even make out some stars in the sky.
In 2003, there was a blackout
that affected large parts of the United States and Canada,
and Todd Carlson lost his electricity,
and he was smart enough to take a picture of his house at that time,
and this is what it looked like.
And again, here you can see this strange, white cloud in the sky
which is the Milky Way.
The lights that we are producing as humans, due to our ingenuity,
are wiping out, basically, our view of these millions of stars in the sky.
So, if we think about that, this is certainly a shame,
because there are a few things that are more magnificent
than a view of the night sky.
But we should also think about what is this doing to our health
if we're flooding ourselves with this amount of light pollution?
So I want to I tell you that all throughout your bodies,
in all of your organs, you have biological clocks
that keep you in sync with the light-dark cycles
of your environment that result from the Earth's rotation.
And in your heads you have a master clock,
a main clock that synchronizes all of these other clocks in your bodies.
The way that this works is that light travels from a source,
such as the Sun, or an artificial light source,
through your eyes,
and that light information is then conveyed to the brain, to the master clock
that's in a part of your brain called the suprachiasmatic nucleus, or the SCN.
So in your eyes you of course have cells that help you see the stars,
that help you form visible imagery.
But you also have cells that are not a part of the visual-forming pathways,
but rather their role is to capture light information
and basically convey it to the brain, to tell the brain what time of day it is.
So, how can I convince you that you have this clock?
Well, if I closed you in a dark room
where you would have no external source of light,
no alarm clocks, no clocks of any kind,
you would still retain rhythmic sleep and wake patterns
at least for a little while,
because your clock was previously trained to light-dark cycles
and one of the main functions of the clock is to regulate behavioral rhythmicity.
This, of course, is not an experiment
that many of you would be willing to subject yourselves to,
but, fortunately, there's an experiment that most of us have participated in,
which is traveling across time zones.
So, I like this quote that says,
"When you travel from America to Europe,
your soul takes about three days longer to get there."
And I know this is certainly true when I travel from here to Serbia,
my home country.
It does take me several days basically, to feel normal,
to feel aligned with the population that's living there.
And this is because your clock takes a few days
to get realigned with this new schedule.
And, if you think about this, this makes sense, right?
So, for pretty much all of our history,
except for a blink of an eye, in our evolutionary history,
nobody had a way of hopping from one continent to the other
in a matter of hours.
We're changing time zones so quickly, and in this case,
nature's not really keeping up with what we are capable of doing.
So, what is this clock? And why is it important to think about light?
The clock is a molecular oscillator, the details here are not important at all,
I don't want you to look at the names of these things on the board,
but I want to point out that the clock
is essentially the same in animals such as fruit flies,
which my lab uses in our studies, and in mammals like mice or humans.
And the first glimpses of the clock, the components of the clock,
and the way that it ticks were gained in the fly, actually.
What I want to stress here
is that the clock is tuned by light.
Some of the components of this clock are actually degraded,
directly degraded by light.
So, that results in the state of the clock
essentially oscillating throughout the day and night.
You can imagine
if the composition of the clock, if some of the components are degraded,
the composition of the clock will change between day and night.
And then the outputs of the clock between day and night will be different.
So, for instance, during the day, the state of your clock is such
that you are suppressing production of melatonin,
which is the hormone that helps you fall asleep,
but also has other functions, such as anti-cancer and antioxidant properties.
So light. Let's talk about blue light a little bit.
When you're outside during the day, you're, of course, exposed to sunlight
which consists of different wavelengths of light.
But the one that's particularly important is blue light,
because of its effect on our clock.
Blue light also directly elevates your mood,
it boosts your attention and your alertness.
So blue light during the day is very, very good,
and I'd say that most of us don't spend enough time in a bright light outside.
You should be for 30 to 60 minutes outside in bright light,
so put some sunscreen on and go outside.
The flip side of this is that when you come home at night
I would dare guess that pretty much none of us
spend the rest of the day when we come home, in darkness,
and we're not in tune with the natural light and dark cycles, right?
So, what we do normally is we use our computers, smartphones, tablets;
we are in rooms that have high amounts of LED light.
And, in particular, what's really bad
is that these devices are very, very rich in blue light.
So, what you're doing, every evening, when you're using these devices
is you're essentially tricking your clock into thinking that it's still day.
And since the clock during day and blue light
suppress melatonin production,
you're essentially doing that at night.
Now, I'm not naive enough to suggest you never use your computer at night,
I know I wouldn't abide by that.
But one thing that you can do,
is you can turn the brightness of your screen in the evening,
you can download programs that filter some of the blue light
or you can use glasses that block some of the blue light.
I have a little bit of news for you that maybe you'll perceive as bad,
but I think it's actually very good,
which is that you are very much like these guys.
So, this is a close-up of a fruit fly,
and you may not like if I tell you that you are like these guys.
But think about it for a second, this is very good for us
because now we can use these animals as a model system
to understand more about sleep biology,
and how light influences our clock and our health,
and this is what my lab is doing.
So, they sleep just like we do, they sleep at night.
If we deprive them of sleep, then they crash the next day
during the time they would normally be active.
If we deprive them of sleep for a long time, they die;
so sleep is very important for them.
The same genes that regulate sleep in humans regulate sleep in flies.
And when they're asleep they're disconnected,
at least to a large degree, disconnected from their environment, just like we are.
So, if these guys are sleeping, you need a stronger intensity stimulus
to get them to react than when they're awake.
So same thing that happens to you of course, when you're asleep.
Two people in my lab: a postdoc, Iris Titos Vivancos
and a PhD student, Michelle Frank,
are asking exactly what is this barrier that's established in the brain
that prevents sensor information from coming through during sleep?
How can your same physical brain exist in two fundamentally different states?
So now we're engaged, for instance, here I'm speaking to you,
I'm engaged, I'm aware of you, of my surroundings,
I'm aware of my internal state;
but tonight when I go to sleep, I will be in a completely different state.
And another thing that we're asking
which is relevant to what I talked about, to light,
is how light coming through the eye is regulating sleep and wake patterns?
A PhD student in my lab, Bryan Song, is asking exactly this,
What Bryan can do is, he can--
you can see that flies have these big eyes that take up a large part of their head.
What Bryan can do is he can actually trick the cells in the eye
into thinking they're seeing light, even when they're not.
And this results in animals having trouble falling asleep,
so it takes them about an hour and a half longer to fall asleep.
You can imagine that now we can use this as a model organism
to understand what it is that happens in the brain
when it's getting light information
and how this is interfacing with sleep and wake centers in the brain.
And so one final thing I want to tell you is
well, first I want you to think again for a moment
about our evolutionary history.
We evolved without alarm clocks,
without any external source of information of the time of day,
and we've developed this way that keeps us in sync with our environment.
But what we're exposing ourselves to every day now
is very much interfering with that natural system,
and I think it's really something to think about.
So when people tell you that too much light exposure at night is not good,
unfortunately, they are actually right.
And the last thing I want to say is please support basic science,
because this is important for all of us, and this is the way forward, I think.
(Applause)