Pleurobot is a robot that we designed to closely mimic a salamander species

called Pleurodeles waltl.

Pleurobot can walk, as you can see here,

and as you'll see later, it can also swim.

So you might ask, why did we design this robot?

And in fact, this robot has been designed as a scientific tool for neuroscience.

Indeed, we designed it together with neurobiologists

to understand how animals move,

and especially how the spinal cord controls locomotion.

But the more I work in biorobotics,

the more I'm really impressed by animal locomotion.

If you think of a dolphin swimming or a cat running or jumping around,

or even us as humans,

when you go jogging or play tennis,

we do amazing things.

And in fact, our nervous system solves a very, very complex control problem.

It has to coordinate more or less 200 muscles perfectly,

because if the coordination is bad, we fall over or we do bad locomotion.

And my goal is to understand how this works.

There are four main components behind animal locomotion.

The first component is just the body,

and in fact we should never underestimate

to what extent the biomechanics already simplify locomotion in animals.

Then you have the spinal cord,

and in the spinal cord you find reflexes,

multiple reflexes that create a sensorimotor coordination loop

between neural activity in the spinal cord and mechanical activity.

A third component are central pattern generators.

These are very interesting circuits in the spinal cord of vertebrate animals

that can generate, by themselves,

very coordinated rhythmic patterns of activity

while receiving only very simple input signals.

And these input signals

coming from descending modulation from higher parts of the brain,

like the motor cortex, the cerebellum, the basal ganglia,

will all modulate activity of the spinal cord

while we do locomotion.

But what's interesting is to what extent just a low-level component,

the spinal cord, together with the body,

already solve a big part of the locomotion problem.

You probably know it by the fact that you can cut the head off a chicken,

it can still run for a while,

showing that just the lower part, spinal cord and body,

already solve a big part of locomotion.

Now, understanding how this works is very complex,

because first of all,

recording activity in the spinal cord is very difficult.

It's much easier to implant electrodes in the motor cortex

than in the spinal cord, because it's protected by the vertebrae.

Especially in humans, very hard to do.

A second difficulty is that locomotion is really due to a very complex

and very dynamic interaction between these four components.

So it's very hard to find out what's the role of each over time.

This is where biorobots like Pleurobot and mathematical models

can really help.

So what's biorobotics?

Biorobotics is a very active field of research in robotics

where people want to take inspiration from animals

to make robots to go outdoors,

like service robots or search and rescue robots

or field robots.

And the big goal here is to take inspiration from animals

to make robots that can handle complex terrain --

stairs, mountains, forests,

places where robots still have difficulties

and where animals can do a much better job.

The robot can be a wonderful scientific tool as well.

There are some very nice projects where robots are used,

like a scientific tool for neuroscience, for biomechanics or for hydrodynamics.

And this is exactly the purpose of Pleurobot.

So what we do in my lab is to collaborate with neurobiologists

like Jean-Marie Cabelguen, a neurobiologist in Bordeaux in France,

and we want to make spinal cord models and validate them on robots.

And here we want to start simple.

So it's good to start with simple animals

like lampreys, which are very primitive fish,

and then gradually go toward more complex locomotion,

like in salamanders,

but also in cats and in humans,

in mammals.

And here, a robot becomes an interesting tool

to validate our models.

And in fact, for me, Pleurobot is a kind of dream becoming true.

Like, more or less 20 years ago I was already working on a computer

making simulations of lamprey and salamander locomotion

during my PhD.

But I always knew that my simulations were just approximations.

Like, simulating the physics in water or with mud or with complex ground,

it's very hard to simulate that properly on a computer.

Why not have a real robot and real physics?

So among all these animals, one of my favorites is the salamander.

You might ask why, and it's because as an amphibian,

it's a really key animal from an evolutionary point of view.

It makes a wonderful link between swimming,

as you find it in eels or fish,

and quadruped locomotion, as you see in mammals, in cats and humans.

And in fact, the modern salamander

is very close to the first terrestrial vertebrate,

so it's almost a living fossil,

which gives us access to our ancestor,

the ancestor to all terrestrial tetrapods.

So the salamander swims

by doing what's called an anguilliform swimming gait,

so they propagate a nice traveling wave of muscle activity from head to tail.

And if you place the salamander on the ground,

it switches to what's called a walking trot gait.

In this case, you have nice periodic activation of the limbs

which are very nicely coordinated

with this standing wave undulation of the body,

and that's exactly the gait that you are seeing here on Pleurobot.

Now, one thing which is very surprising and fascinating in fact

is the fact that all this can be generated just by the spinal cord and the body.

So if you take a decerebrated salamander --

it's not so nice but you remove the head --

and if you electrically stimulate the spinal cord,

at low level of stimulation this will induce a walking-like gait.

If you stimulate a bit more, the gait accelerates.

And at some point, there's a threshold,

and automatically, the animal switches to swimming.

This is amazing.

Just changing the global drive,

as if you are pressing the gas pedal

of descending modulation to your spinal cord,

makes a complete switch between two very different gaits.

And in fact, the same has been observed in cats.

If you stimulate the spinal cord of a cat,

you can switch between walk, trot and gallop.

Or in birds, you can make a bird switch between walking,

at a low level of stimulation,

and flapping its wings at high-level stimulation.

And this really shows that the spinal cord

is a very sophisticated locomotion controller.

So we studied salamander locomotion in more detail,

and we had in fact access to a very nice X-ray video machine

from Professor Martin Fischer in Jena University in Germany.

And thanks to that, you really have an amazing machine

to record all the bone motion in great detail.

That's what we did.

So we basically figured out which bones are important for us

and collected their motion in 3D.

And what we did is collect a whole database of motions,

both on ground and in water,

to really collect a whole database of motor behaviors

that a real animal can do.

And then our job as roboticists was to replicate that in our robot.

So we did a whole optimization process to find out the right structure,

where to place the motors, how to connect them together,

to be able to replay these motions as well as possible.

And this is how Pleurobot came to life.

So let's look at how close it is to the real animal.

So what you see here is almost a direct comparison

between the walking of the real animal and the Pleurobot.

You can see that we have almost a one-to-one exact replay

of the walking gait.

If you go backwards and slowly, you see it even better.

But even better, we can do swimming.

So for that we have a dry suit that we put all over the robot --

(Laughter)

and then we can go in water and start replaying the swimming gaits.

And here, we were very happy, because this is difficult to do.

The physics of interaction are complex.

Our robot is much bigger than a small animal,

so we had to do what's called dynamic scaling of the frequencies

to make sure we had the same interaction physics.

But you see at the end, we have a very close match,

and we were very, very happy with this.

So let's go to the spinal cord.

So here what we did with Jean-Marie Cabelguen

is model the spinal cord circuits.

And what's interesting is that the salamander

has kept a very primitive circuit,

which is very similar to the one we find in the lamprey,