Seeing a fish's thoughts - The Naked Scientists

13/02/13 0:06

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Seeing a fish's thoughts
Thu, 31st Jan 2013

Ginny Smith
A new imaging technique has allowed scientists to see thoughts occurring in real time as fishcontemplate their prey.
Japanese researcher Akira Muto and colleagues, writing in current biology, genetically engineered zebra
fish to produce a glowing green label called GFP in an area of the brain called the optic tectum, whichis involved in decoding vision. The green glow was switched on whenever nerve cells in this part of thefish brain became active, meaning that different regions of the optic tectum quite literally “lit up” when
the fish looked at different things.
What did they find?
First, they showed that the brain cells in the optic tectum responded when a spot was flashed on andoff in the fish’s visual field. They then moved thespot around and found that the area that lit up also
moved around this region of the brain.
This is known as “topographic mapping”. It occurs
because the brain is laid out like a map of thefish’s visual world, so one part of the eye always
sends signals to the same part of the brain.
They also offered the fish a “paramecium”, which
is a small organism that young zebra fish like to eat. When the paramecium moved around in front of
the fish, nerve cells lit up in the optic tectum on the opposite side to the side the prey was on. This isbecause the brain is cross-wired- the left hemisphere controls the right side of the body, and vice versa.
And when the fish began its prey capture behaviour: approaching the prey and pursuing it with its eyes,
one particular part of the tectum, towards the rear, always became active. The researchers suggest that
this area may therefore be connected to a brain region that produces these prey capture behaviours.
This technique could also be used to look at other regions of the brain, as fish can be bred to express
the fluorescent protein in other areas of interest. It is particularly useful as you can see the changes inreal time, and it is relatively non-invasive, so the animals can be studied when behaving in a naturalway. This allows researchers to find out more about how the brain controls movement and hunting.
Why did they use zebra fish?
Zebra fish are rather special as they are transparent when they are in the embryonic and larval stagesthat is before they are fully grown. They also grow rapidly, and a fertilised egg can become a fish ableof catching prey after only 4 days. This means that fish can be bred with this fluorescent protein, andyou can actually watch them, under a microscope as they are very small, and see which bit of theirbrain glow when they see different moving or stationary stimuli!

References
Real-Time Visualization of Neuronal Activity during Perception Akira Muto, Masamichi Ohkura, Gembu
Abe, Junichi Nakai, Koichi Kawakami Current Biology - 31 January 2013
http://dx.doi.org/10.1016/j.cub.2012.12.040

Comments
Unfortunately that dead fish saga is one of the most important experiments in the field - it showsthat the parameters determined and generally agreed were rubbish.
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Seeing a fish's thoughts - The Naked Scientists

13/02/13 0:06

imatfaal, Tue, 5th Feb 2013

Probably somewhat more effective than doing neuro-imaging on dead fish.
I like the idea of being able to observe the fish brain activity when the fish are more or less acting
normally. An EEG, or MRI might be difficult to do in the water while the fish are active, especiallywith small fish.
However, if the the fish is mostly transparent, what about adding some kind of contrast to theblood... could one see the blood flow in the brain, somewhat like a PET or FMRI, without all theexpensive equipment?
CliffordK, Fri, 1st Feb 2013
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