Scientists Map Neural Activity In Behaving Zebrafish
If you have always wondered what your fish was thinking, then this new study published in the scientific journal Neuron will soon tell you. Neuroscientists from the Champalimaud Foundation and Harvard University, have described the first neural activity maps at the resolution of single cells and throughout the entire brain of freely behaving zebrafish, according to a press release Wednesday..
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"This opens up new possibilities for studying neural circuits in the brain," said Michael Orger, principal investigator at the Champalimaud Neuroscience Programme. "In order to understand how the brain works, it is imperative that we can record the activity of the cells of the brain - the neurons, and at the same time be able to relate that to an animal's behavior. Now, we can systematically record activity through the whole brain of the zebrafish, which contains about one hundred thousand neurons, while at the same time we are monitoring its movements using high speed video."
This study is path breaking since until now, available methods did not allow monitoring activity of the entire brain but only a small fraction of the neurons in the brain.Claudia Feierstein, a postdoctoral fellow in the lab of Dr. Orger explained, "by watching the brain while the fish tries to follow rotating visual patterns by moving its eyes and tail, we were able to identify the specific brain structures that are involved in these behaviors, and how different patterns of activity reflect the different aspects of sensory and motor processing."
Since this method allows mapping the brain activity of a single fish, rather than piecing together neuron activities of multiple experiments, it is possible to compare the neural circuit organization across different individuals. "When we talk about brain activity maps an important question is to what extent the circuits in different animals are similar. How precisely can we predict where we will find particular neurons from one brain to another?" said Dr. Orger.
A surprising find was that while the network of neurons controlling simple visual -motor behaviors is widely distributed across the brain, it is almost similar between individuals. "If you identify a region with a particular pattern of activity in one fish, you can typically find neurons with the same activity within a few micrometers in the brain of another fish", says coauthor Ruben Portugues, a scientist from the group of Professor Florian Engert at Harvard.
This is an important find, because neuroscientists can build a detailed functional map of the brain and locate and target specific groups of neurons. This map of functional "blocks" can also be aligned with existing maps of gene expression to assign behavioral roles to different cell types in the brain.
This systematic approach to mapping activity also enables researchers to discover rare cell populations that were till now, unknown. "We found a handful of neurons in the main visual processing area of the fish brain, called the optic tectum, that integrate motion information from both eyes. This was surprising since this area only gets direct information from one eye. These cells are few in number, but may play an important role in the behavior of the animal, since they allow him to decode how he is moving through the water", said Dr. Orger.
The next project for the researchers is to use optical and genetic manipulations on specific neurons, like the optic tectum, to find out how the brain processes sensory information to generate appropriate movements.
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