This episode was made in partnership with The Kavli Prize.
The Kavli Prize honors scientists for breakthroughs in astrophysics, nanoscience,
and neuroscience – transforming our understanding of the big, the small, and the complex.
In the early 1970s, computers were suddenly everywhere.
People saw a lot of promise in these machines that took an input like a keystroke,
passed messages along a series of wires,
and resulted in an output, like displaying that letter on a screen.
Neuroscientists also saw something that appeared familiar:
the wiring of the human nervous system.
The way our neurons take an input, pass electrical messages between neurons in a
specific sequence, and then deliver an output seemed very similar to a computer.
Scientists came to think of the brain that way, and of behaviors as being “hardwired.”
But as satisfying as the one input, one circuit, one output comparison was,
researchers soon realized that the millions of things our nervous system can do
would require more hardwired circuits than it could possibly contain.
An innovative neuroscientist named Eve Marder had a completely different theory
for how our nervous systems work.
And to prove it, she needed—of all things—crab stomachs.
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Think about walking for a second.
All the muscles in your legs, ankles, and feet have to be able to move up, down,
left, right, at a 37 degree bend, faster, slower, with more or less pressure
so that you can adjust to the terrain without losing your balance.
Walking is a behavior – an action or response to the environment.
And understanding how those behaviors are produced
is important for knowing how to fix them when they go wrong.
We’ve known for a long time that brain activity involves electricity.
Anatomists could see the networks of nerves
connecting to one another and to muscles throughout the body.
So it was appealing to imagine electricity
traveling along those just like it does wires in a circuit.
The brain would produce an instruction, the “wires” would carry the signal,
and the result would be some behavior.
That intuitive idea was the base assumption in neuroscience around the 1970s.
But it began to fall apart as researchers
developed a better understanding of neuroanatomy.
If human bodies were wired like a circuit board, you’d have one circuit
for each of those kinds of walking – go slow, go fast, go up a slope, and so on.
Soon, researchers could see there weren’t enough neurons in the body for that.
Second, everyone’s nervous system is “wired” a little differently.
But give or take some differences in ability between us,
all our “circuits” always produce the same behavioral results.
Small differences in individual bodies get overridden.
Finally, while individual neurons live for our whole lives,
they’re still cells that have parts that wear out and need to be replaced.
But neurons aren’t like Formula 1 cars
that get to take a quick break to swap out parts.
Somehow they manage to put new tires on while they’re still driving.
None of those things made sense if you had one circuit producing one behavior.
A circuit board just couldn’t explain all that adaptability.
It wouldn’t keep working as it’s being repaired,
or work at all if the system didn’t have an impossible number of circuits.
So it was kind of a mystery how the nervous system accomplished these feats.
And it was a mystery Brandeis University professor Eve Marder
was determined to solve.
Marder’s research focused on the stomatogastric ganglion, or STG,
a group of about 30 neurons connected to a crustaceans’ stomach.
The STG neurons control chewing, sort of.
Crabs and lobsters don’t chew with their mouths and then swallow.
Instead, muscles in their stomachs expand and contract
to grind their dinner into digestible pieces.
And one nice thing about these STG neurons is that they keep doing their thing
even when you pull them from the organism and study them in a lab.
Marder researched the activity of the neurons as they were influenced
by neuromodulators – molecules that influence what neurons do,
like the neurotransmitter dopamine.
At the time, most neuroscientists thought of neuromodulators
as working on individual neurons.
Molecule A goes into neuron slot B and makes that neuron send out
an electrical signal that tells the next neuron what to do, and so on down the line.
They were thought to just be carrying the signal to create the behavior,
like an old-timey bucket brigade putting out a fire.
In the circuit-board view, that same chain of the exact same neurons
would pass a signal every time molecule A went into neuron slot B,
and it would always end in the same behavior.
But Marder found that neuromodulators were influencing
the entire group of STG neurons together.
Instead of a circuit that just passed a signal along, the neuromodulator
was talking to everybody at once, and everybody had a slightly different reaction!
One neuron might have its activity turned up
and another turned down by the exact same molecule.
That meant the muscles in those crustacean stomachs could produce
a whole bunch of different outcomes with one very simple neural circuit.
The implications for our own nervous systems were clear.
Marder could now prove how we get really fine-tuned behavior,
like the many different ways to walk,
without needing a nearly infinite number of different neural connections.
Her work also addressed how different individuals
could produce the same behaviors.
In general, the crabs and lobsters she worked with
weren’t bred to be as identical as possible, like most lab animals are.
Instead she got them from the wild, straight from fishing boats.
And like most wild creatures,
those crustaceans had a lot of variability in their nervous systems.
Since all crabs do crab things, studying wild crabs allowed her to explore
how different circuits could be and still result in the same behavior.
As it turned out, some of the individual crabs had connections
between some of their neurons that were six times stronger than other crabs.
But the difference didn’t matter.
Both circuits had the same result.
So there are multiple solutions, multiple pathways,
that can get you to the same point.
Which isn’t just important between individuals.
It’s also important within individuals.
This explained how, as individual parts of our neurons wear out
and are swapped, they keep functioning.
They can create the same end result from a different circuit or part of a circuit.
Since Marder’s discovery, neuroscientists have been busy
using that new understanding of how the nervous system
works to investigate all kinds of problems with the human nervous system.
For example, understanding how neuromodulators
create flexibility in the nervous system could benefit stroke treatment.
When someone experiences a stroke,
part of their brain gets cut off from blood flow and oxygen.
If it’s cut off long enough, those neurons die.
But we know that after a stroke,
the brain can make new connections that allow it to compensate for what was lost.
It doesn’t have to rebuild the same circuits.
Marder’s insights could help researchers figure out how to
rebuild those new connections to fill in the gaps more efficiently.
And as Marder continues to study wild-caught animals,
she’s also interested in how they are affected by the changing climate.
For her work describing how nervous systems both change and stay the same,
Eve Marder was awarded the 2016 Kavli Prize in Neuroscience.
And deservedly so!
Because science is kind of like the way we’ve thought about our nervous system.
When we keep doing things the same way, we get the same outcome.
One input, one circuit, one output.
But with a few changes to how we think about things,
entirely new pathways are possible.
Thanks for watching this episode of SciShow!
And thank you again to The Kavli Prize for supporting this episode.
The Kavli Prize in Neuroscience is awarded for outstanding achievement in
advancing our knowledge and understanding of the brain and nervous system.
They also award a nanoscience and astrophysics prize,
honoring researchers for transforming our understanding of the science of atomic,
molecular and cellular structures, and advancing our knowledge of the origin,
evolution and properties of the universe.
If you want to learn more about
Dr. Marder’s work, you can visit her page on the Kavli Prize website
by clicking the link in the description.
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