Translator: Shuai Shao Reviewer: Rhonda Jacobs
What a beautiful city!
I wish I could go there and take a week-long vacation.
How many of you went somewhere for your summer vacation?
Please raise your hands.
And how many of you used a map during your trip?
OK, most of people.
So these days maps are great.
You can basically get all the information that you need.
You can see how cities are connected with each other,
buildings are connected with each other.
You can find great local restaurants with good rating.
And you can even see their menus.
And share your experience and findings with other travelers
using this map platform.
You won't be able to imagine traveling without a map.
How about your smartphones?
You can't live a day without it, right?
What if you dropped your smartphone on your way to work,
and it stopped working?
So you took it to a repair shop,
and what if no one can fix it
because nobody knows what kind of components are in there
and how they are connected with each other?
It will be a complete disaster.
Some of you may work at a large factory that has all sorts of machines.
What if nobody in your company knows what kind of machines you have,
and the function of these machines,
and how they are connected with each other?
If something goes wrong,
you probably have to shut down the factory.
But luckily for all these human created systems,
we have comprehensive maps.
How about our brain?
It's probably the most complex system in the universe.
It consists of 200 billion cells,
100 billion neurons,
each making tens of thousands unique connections
with thousands of other neurons.
And it's not surprising that this complex system often fails.
There are over 600 neurological disorders.
And at some point of your life,
all of you will be touched by some of these neurological disorders,
one way or another.
For example,
one in three of us will eventually get Alzheimer's disease
or the other forms of dementia.
And there's currently no effective treatment
and all recent clinical trials have failed.
So we certainly need a great map that could help us better understand our brain.
So today in the next few minutes,
I will share the journey that my team and other neuroscientists have embarked on
to establish such brain maps.
And it all started over a century ago by Santiago Ramon y Cajal,
who is considered the father of modern neuroscience.
For the first time, he observed microscopic details of neurons
in thin brain slices under a microscope.
And he and other neuroscientists hypothesized that the secret of our brain
is hidden in the connections of these beautiful neurons
with breathtaking diversity.
And in 1986,
a century after Ramon y Cajal's remarkable discovery,
the first connectivity map was established
for this small worm, called C. elegans.
This worm is one millimeter thick and one millimeter long,
and it's as thin as your hair.
And its nervous system contains about 302 neurons.
And in 1980 and 70s,
a group of researchers sliced this worm into thousands of thin slices.
And then they imaged all these slices using very powerful electron microscope.
And then after a decade-long manual reconstruction and training,
they finally established a complete circuit map,
shown here.
And this diagram, its dots represent neurons.
And each line shows the connectivity between neurons.
And this map called C. elegans connectome
had remained the only complete circuit map until recently.
This year a group researchers used advanced form of electron microscopy
to map an image, brain of fruit fly,
which is 10 times larger than C. elegans.
Can we now use these advanced electron microscopy technologies
to map the human brain?
The challenge here
is the sheer size of the human brain.
Mouse brain is 10,000 times larger than fruit fly brain.
And human brain is 10,000 times larger than a mouse brain.
So although this technology has been rapidly evolving,
it will take a while for us to use this technology
to map a large volume of human brain.
But don't worry,
there are other powerful technologies that we can use.
In 1990s, researchers discovered that we can put a gene from a jellyfish
that expresses florescent proteins to color neurons.
And now a palette of florescent proteins are available,
and we can use them to label neurons with many different colors.
And if you can image this beautiful relabeled brain
at high enough resolution
to see every single wires,
and if you follow it from one end to the other,
you can actually map the connections between brain regions and neurons.
And imaging this - the entirety labeling neurons in C. elegans
is easy, relatively easy,
because C.elegans is really small,
and its body is transparent.
But doing so in a mouse brain is much more challenging
because as I said,
mouse brain is 10,000 times larger than C. elegans,
and it is not transparent.
So what we did is we developed a technology
called Clarity that transforms this non-transparent tissue
into optically transparent jello,
while preserving tissue architectures.
So on the left, you see a mouse brain before Clarity,
and on the right image,
there is a brain, Clarity-processed, but it's almost invisible
because it's really transparent.
And once brain becomes this transparent,
you can image the inner structures under a microscope.
And here we used Clarity
to clear a genetically engineered mouse brain
that expresses fluorescent proteins
in subset of excitatory neuron cells.
And here I'm showing a 3D rendering of half of the mouse brain.
And as we approach to this brain,
you can see green labeled cells
and their processes, their projections.
And using this Clarity technology,
you can visualize the distribution
of these green fluorescent protein-expressing cells
and their broad connectivities.
And in some areas,
where the density of labeling is low,
you can actually see individual fibers.
But still the density is too high,
it's very challenging to reconstruct individual fibers
in this dataset.
And instead of using this genetically engineered mouse,
you can actually use the virus to label a small number of neurons
in specific target area.
In this method, what we do is
we use fine needle to inject virus into a target brain region.
And this virus contains a gene of fluorescent proteins.
And only virus-infected neurons express fluorescent proteins and glow.
So we are going to zoom in in this area,
and I will show you a movie
that hightlights the details of these labeled neurons and their projections.
So here you see a series of optical sections
moving in and out of this dataset.
And here on the left you see neurons labeled with red fluorescent proteins.
And they are sending wires to the downstream brain regions
in the middle of middle and the right side of this screen.
And now I'm showing a series of optical sections.
You can see one [inaudible] cell bodies,
and they are sending fibers to the downstream brain regions.
And at this resolution, you may think
that all these red fluorescent proteins-expressing neurons
have similar properties.
They are all clustered in one brain region.
And they are sending fibers to the similar brain regions downstream.
But if you carefully follow individual fibers,
you can actually notice
that the projection pattern of these individual neurons is quite different.
And we ultimately want to reconstruct these projection patterns
at a single cell resolution
because this connectivity projection pattern is an important factor
that determines the function of neurons.
But accurately tracing these fibers is not easy,
because it requires imaging a large intact tissue
at extremely high resolution.
If the resolution is not high enough,
you cannot distinguish these fibers.
So in this image, if I ask you to pick one green fiber
and follow it from one end to the other,
you won't be able to do so
because these fibers look fuzzy.
We need higher resolution to accurately trace these fibers.
So to address this challenge,
we and others have developed a technology that physically expands tissue
while preserving their intercellular connectivity.
Our technology called MAP
can transform the small mouse brain shown on the top
into this giant jello in the middle of the screen,
while preserving neural connectivity.
And this physical expansion allows us significantly enhanced resolution
of these images as you can see here.
So now if I ask you to pick one fiber and trace them, you can actually do it.
So we use this "MAP" technology to map -
if we put these images side by side,
you can better appreciate the power of the MAP technology.
So we use this technology MAP to map the projection pattern of a single neuron.
And here this white squiggly represents axonal projection,
the five wiring is coming out of one single neuron.
And you can think of this image as a satellite view of a Google map.
And this I would call a map view of a Google map.
And here you can clearly see where this neuron is projecting to
and what are the downstream neurons that are connected with this neuron.
So can we use this fluorescent protein technology
to map the human brain?
Unfortunately, the answer is no.
Because any genetic manipulation of human cells is invasive.
None of you would volunteer
to have your skull drilled for viral injection.
So we need different strategy.
And luckily we have a very powerful tool called antibody.
Antibody is a protein produced by immune cells,
and they can recognize specific target proteins.
And using fluorescent dye labeled antibodies,
we can label different cell types
and their subcell architectures in human brain.
So from now I will show you how we can potentially
use these technologies to generate comprehensive human brain map
at unprecedented resolution.
So here we have a large thick human brain tissue.
Now, first thing that we are going to do
is turn this into optically transparent hydrogel.
And after that,
we will use molecular probes like antibodies and dyes
to label and visualize cells and other structures.
And here I will zoom in so that you can see microscopic details.
So here we use two dyes.
We use red to visualize blood vessels,
and we use green to label all cell nuclei.
And as we zoom in,
now you can clearly see individual cells and microvasculature.
And you can see that the density of the cells and blood vessels
is extremely dense.
In this data set,
all cells labeled green look similar,
look the same.
But as I - as we discussed,
there are many different types of cells.
And we can reveal the identity of these cells
only when we use antibodies
that recognize specific molecules expressed in specific cell types.
So after this mapping,
what we are going to do is we will strip out these immersive dyes
and then use a host of antibodies
to label many different cell types.
So we are going to zoom in further so that you can see individual cells.
And here we are using many different antibodies
to label different cell types and structures.
And now, using this technology,
we can reconstruct the 3-dimensional distribution of cells
and how the composition of tissue is -
the tissue is composed.
But we want to zoom in further.
We want to see the morphological details of neurons and their connectivity.
So we are going to zoom in again,
and then,
at this high resolution,
now we can see the morphological details of antibody-labeled neurons.
And we can reconstruct their projections at single-fiber resolution.
So how small is this data set,
this volume,
compared to the brain chunk that I showed you?
It's really, really small.
And how small is this data set, this brain chunk data set,
compared to the entire human brain?
It's pretty small.
So using our current technologies,
it will probably take many years to map the entire brain at this high resolution.
But I believe that we can significantly increase the speed of brain mapping
and drop the cost sharply by continuously developing these technologies.
What do you see in these containers?
Any guess?
Yes, human brains.
Each container has one human brain.
Some are from, probably, Alzheimer's disease patients.
Some are from children with severe autism spectrum disorders.
Currently, there are tens of thousands of brains
stored at hundreds of brain banks worldwide.
And every year,
a number of people donate their brains
hoping to contribute to the advancement of neuroscience research
and the development of cures for neurological disorders.
Actually, I worked with clinicians at Mass General Hospital.
And at the Mass General Hospital alone,
there are over 400 brain donors every year.
And one day we will be equipped with technologies that are powerful enough
to map all these brains at unprecedented resolution and completeness.
And I have no doubt that these incredible resources
will accelerate the advancement of neuroscience research
and the development of [new scientific] strategies.
Thank you.
(Applause)