Fish Watches Food. Scientists Watch Fish’s Thoughts – Phenomena: Not Exactly Rocket Science

13/02/01 20:51

PHENOMENA: NOT EXACTLY ROCKET SCIENCE
MENU

CREDIT: SHAWN BURGESS, NHGRI
Larval zebrafish

NOT EXACTLY ROCKET SCIENCE: 19 hours ago

Fish Watches Food. Scientists Watch Fish’s Thoughts
by Ed Yong

A baby fish watches a tasty cell swimming in front of it. Neurons fire in its brain, and it
recognises a potential meal. Its eyes converge, it beats its tail, and it heads in for the kill.
Trillions of baby fishes have enacted this little tableau for half a billion years, but thisindividual is special. It has been altered by a team of Japanese scientists so that its
neurons give off a flash of light whenever they fire. And since its head is transparent, any
onlooker can see its brain activity. In doing the rather mundane task of capturing a meal,
this fish is putting on a nifty real-time lightshow. It’s showing us what a thought looks like.
At the moment, if you want to visualise the brain, you have to sacrifice detail. Scanningtechniques like fMRI measure the flow of blood to millions of neurons and, despite
producing pretty, blobby diagrams, their resolution is terrible in space and time.
Alternatively, you can record the activity of single neurons, or perhaps even a handful, butthat tells us little about the rich networks that allow us to think and compute.

http://phenomena.nationalgeographic.com/2013/01/31/fish-watches-food-scientists-watch-fishs-thoughts/

ページ 1/13

Fish Watches Food. Scientists Watch Fish’s Thoughts – Phenomena: Not Exactly Rocket Science

13/02/01 20:51

What you want is to combine the fine detail you get from zooming in, with theoverarching view you get from zooming out. You want to visualise the brain, or even abrain region, at the level of single neurons. And that’s impossible, at least in humans.
Akira Muto from the National Institute of Genetics in Shizuoka, Japan has taken a step
towards this goal in the larval zebrafish.
These tiny animals, whose brains are a fraction of a millimetre across, have a seductive
allure for neuroscientists. Their bodies are transparent, giving a direct window into theirbrains. And those brains are small, with just 300,000 neurons compared to our 86 billion.

A firing neuron lights up in the brain of a zebrafish larva. The image has been coloured. Credit: Muto et al., Current Biology

The team began by tweaking a jellyfish protein called GFP so that it gives of a bright green
glow whenever it detects a rise in calcium ions, as happens when neurons pass signals toone another. GFP has been a workhorse of biology for decades, but the team produced an
exquisitely sensitive version. They also targeted the protein to the fish’s optic tectum – thepart of its brain that receives signals from its eyes. Whenever the zebrafish saw somethinginteresting, any firing neurons in its tectum would start to glow.
First, Muto checked how it reacted to a tiny spot projected onto a screen next to it. He
http://phenomena.nationalgeographic.com/2013/01/31/fish-watches-food-scientists-watch-fishs-thoughts/

ページ 2/13

Fish Watches Food. Scientists Watch Fish’s Thoughts – Phenomena: Not Exactly Rocket Science

13/02/01 20:51

focused on the neuropil, an area where the tectum’s neurons hook up to those comingfrom the retina. By all accounts, the neuropil should act like a map of the space that thefish can see. Neurons on the far left, for example, should fire and glow when the fish sees
something moving on its far left.
That’s exactly what Muto found. As he moved the spot up and down, the neuropil’s green
glow also moved up and down. As the spot shook from left to right, the glow shook fromleft to right. The technique was even sensitive enough to identify individual neurons thatare tuned to specific directions of movement, firing only when the spot zigged in one way
but not when it zagged in the other.
The glowing protein worked. Now, for a real test. Muto tempted the fish with aparamecium—a single-celled creature that swims around by waving tiny hairs. As the celldanced in front of the immobilised larva, the glow of active neurons followed its path.
You can see this in the video below. The fish’s brain is the blue and purple blob at thebottom of the screen, and the paramecium is the violet speck darting madly all around it.
As neurons fire, small patches of white and red show up. That’s the fish spotting a moving
object. You’re watching an act of a perception in a living animal on your screen.

Note that when the paramecium is on the left of the fish, the neurons on its right side fire,and vice versa. That’s what happens in our brains too – the signals from our eyes crossover into the opposite half of the brain.
http://phenomena.nationalgeographic.com/2013/01/31/fish-watches-food-scientists-watch-fishs-thoughts/

ページ 3/13

Fish Watches Food. Scientists Watch Fish’s Thoughts – Phenomena: Not Exactly Rocket Science

13/02/01 20:51And if the paramecium stayed still next to the fish’s eye, its brain never fired. Like a
Hollywood tyrannosaur, its vision is sensitive to movement.
If Muto unchained the larva, and allowed it to actuallycatch the paramecium, something slightly different
happened. Just as its eyes converged and it darted
forward, the front-most parts of its tectum became active.
This region may contain specific circuits that control thelarva’s prey-capture routine.
Other groups have managed to film a zebrafish’s brain
activity while it watched artificial visuals, like a set ofmoving stripes. This is the first study to show us how its
neurons behave towards a natural object—theCredit: Muto et al, Current Biology.
paramecium. The team also say that their new version of
GFP is more sensitivity than older ones, and has a better resolution. However, Ed Boyden
from MIT points out that they haven’t shown any detailed comparisons with popular
existing tools. “It’s a little bit unclear to me whether the ability to image the visual
response to a natural object was enabled.
Regardless, Muto’s team are ploughing ahead. The tectum is a good place to start because
it’s organised in a predictable way, and because perception is an easy act to test—just sticksomething in front of the fish and let it perceive. The team is now developing ways oftargeting their glowing protein to other parts of the brain, so they can identify the circuitsthat are involved in movements, decision-making and other behaviours. And they hopethat they’ll eventually be able to visualise the entire brain at once.
Other neuroscientists, like Boyden, are working on their own technologies for mapping
the brain, but this is a step in the right direction. And it’s another sign that the humble
zebrafish might help neuroscientists as Virginia Hughes wrote in her superb recent
feature, “to answer the biggest question in neuroscience: how a doughy mass of neurons
in the brain gives rise to an exquisite suite of behaviours, absorbing information from theoutside world and generating responses.”
Reference: Muto, Ohkura, Abe, Nakai & Kawakami. 2013. Real-Time Visualization of
Neuronal Activity during Perception. Current Biology
http://phenomena.nationalgeographic.com/2013/01/31/fish-watches-food-scientists-watch-fishs-thoughts/

ページ 4/13

Fish Watches Food. Scientists Watch Fish’s Thoughts – Phenomena: Not Exactly Rocket Science

13/02/01 20:51

http://dx.doi.org/10.1016/j.cub.2012.12.040
More on visualising the brain:
The Where of What: How Brains Represent Thousands of Objects
The brain is full of Manhattan-like grids‘Brainbow’ paints individual neurons with different colours
Like79273

Add Your Comments
All fields required.
YOUR NAMEYOUR EMAILYOUR COMMENTSSUBMITNOTIFY ME OF FOLLOW-UP COMMENTS BY EMAIL.

NOTIFY ME OF NEW POSTS BY EMAIL.

RELATED POSTS

http://phenomena.nationalgeographic.com/2013/01/31/fish-watches-food-scientists-watch-fishs-thoughts/

ページ 5/13

Fish Watches Food. Scientists Watch Fish’s Thoughts – Phenomena: Not Exactly Rocket Science

13/02/01 20:51

NOT EXACTLY ROCKET SCIENCE: 17 hours ago

The Real Wisdom of the Crowds
In 1907, Sir Francis Galton asked 787 villagers to guess the weight of an ox. ...

Read more

http://phenomena.nationalgeographic.com/2013/01/31/fish-watches-food-scientists-watch-fishs-thoughts/4

ページ 6/13