Open up! Scientists first reveal the complete animal nervous system

:2019-07-05

There is an irrefutable truth in the field of biology - structure determines function.

The structure of the wings determines how to fly, the structure of the lungs determines how to breathe; the structure of the protein determines the function of the enzyme, and the structure of the DNA determines how the gene works.

The structure of the nerve determines how we think, learn, exercise, and even determine the occurrence of some diseases.

This is the core of the so-called "connectomes": by mapping the brain's regions and the myriad of neural connections in the nervous system to find specific neural circuits that lead to specific behaviors.

Today, Connected Groups is welcoming a milestone breakthrough. The research team of Professor Scott Emmons of Albert Einstein College of Medicine was published on the cover of Nature magazine [1], which completely unveiled the mystery of the animal nervous system for the first time. The study provided all the neural connections of the two sexes of Caenorhabditis elegans from sensory input to terminal output, and conducted a multi-level analysis of the behavioral regulation network.

Surprisingly, the neuromodulation complexity of exercise far exceeds the previous imagination, and it is still a long way to go to get a specific neural connection from a spider network-like neural network.


Source | nature.com

Long before the word "connected group" appeared, scientists had wanted to break the nervous system.

In the 1970s, scientists reached out to the Caenorhabditis elegans. Nematodes have complex physiological behaviors while the structure is quite simple. A nematode adult is only about 1 mm in size, and there are only 1000 cells in the body. One third of them are neurons, which is an ideal experimental object.

The nematode's neurons are too small to be seen under the light microscope, so the scientists fixed it and cut it into a thin layer of hair, and photographed it with an optical microscope.

The next steps are a bit more rude and costly. Scientists use the naked eye to identify individual neurons and the connections between them, drawing more than 5,000 synapses in one stroke. The work was published in 1986 and was hosted by Sydney Brenner, who later won the Nobel Prize in Physiology or Medicine in 2002.


Sydney Brenner (1927-2019), who shared the 2002 Nobel Prize in Physiology or Medicine for his contribution to the key genes that regulate organ development and programmed cell death, and developed nematodes as the number one hero of ideal animal models.

But this research report is not perfect.

First of all, the human eye has limits. This "neural map" was later proved to be imperfect. Secondly, the nematode has two genders. Brenner only studied one of the hermaphrodite.

Obviously, this is not enough for us to see the complete way the nervous system works.

In order to solve these problems, the Emmons team developed software that can map neurons more accurately. In 2012, the neural connection group data of the male tail of the nematode was published. The paper was published in Science [2].

On the one hand, the electron micrograph of the male nematode was re-made, and on the other hand, Brenner's old data was analyzed. Today we finally saw the first complete connection diagram of the animal's nervous system, including the connections between the neurons, from the neurons to the muscles. Connections with other tissues, connections between muscle tissue, and estimates of the strength of these connections.


Androgynous nematode

Obviously, the neurological differences caused by gender differences are huge.

The androgynous nematode has 302 neurons, of which 8 neurons and 12 muscles are special; male nematodes have 385 neurons, of which 91 neurons and 39 muscles are special.

The neuronal differences between the two are mainly in reproductive-related functions and organs, but there are also differences in the intensity of neural pathways shared by many genders, which may be one of the causes of behavioral differences. The researchers estimate that the gender difference in the nervous system should be between 10% and 30%.

The researchers also detailed the information transmission between the neural networks of the nematodes at various levels, and the content is quite academic and not developed here.


Male nematode

Another interesting point is that the network of connections between neurons is very complex, not as clear as a circuit diagram or a machine learning network, but rather a complex spider web.

There is a saying that there is only a six-layer relationship between any two people in the world. Applying this sentence, we can also say that there is at most one neuron between any two neurons of the nematode.

The close connection of the neural network allows a single sensory neuron to reach 70% to 98% of any other neuron with only two synapses.

Such a complex network, from which to determine the neural pathways that regulate specific behaviors, is a needle in a haystack. This step must be combined with more neuroscience tools, such as fluorescent indicators.

By superimposing these real-time neural activities on the connected omics data, we may hope to create a virtual nematode that "lives" in the computer, and then it is no longer difficult to fully resolve the nerve activity.


True nematode

The Emmons team is ready to continue to study the relationship between neural connections and gene expression. At the same time, in every corner of the world, different scientists are working hard to overcome the neural maze of other experimental animals such as fruit flies and mice.

In 2010, NIH allocated $40 million to map human brains. The human brain has tens of billions of neurons and trillions of synapses, far more complex than nematodes. This is another star in the sense of the sea.

The distance is completely understood, although it is still far away, but we have already stood at the starting point.

Source: Singularity Network

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