Only one organism has succeeded in mapping all nerve cells. What is 'Connectome', which is a powerful data for neuroscience?

In 2020, a neuroscientist at Harvard University and an engineer at Google jointly presented a stained and mapped version of a nerve cell in the human brain. However, the mapping done in this collaborative study is only one millionth of the entire human brain. Quanta Magazine, a scientific media, explains what the 'Connectome' that maps nerve cells looks like.

New Brain Maps Can Predict Behaviors | Quanta Magazine

Jeff Richtmann and colleagues at Harvard University, who conducted the Connectome, cut the human brain into more than 5,000 pieces and succeeded in mapping by imaging blood vessels and nerve cells that could be observed with an electron microscope. Lichtmann, who has been with Connectome for many years, was pleased with the results, saying, 'It's like discovering a new continent,' but he admits that it takes much longer to map the entire human brain.

Knowing how nerve cells are arranged and how they are connected to each other is the key to understanding how the organism that owns the brain thinks, feels, and behaves. It is said to be. One experiment showed the possibility of predicting the next behavior of an animal from the Connectome, and another experiment showed the possibility of deriving certain rules for the operation of nerve cells from the Connectome. Mapping the entire brain is essential for pursuing this kind of knowledge, but the reality is that only one species has succeeded in doing so. The organism is a species of nematode with a body length of only 1 mm.

The nematode Connectome dates back to 1986 . Mapping is performed on nematodes with only 302 neurons, and all sites are arranged in any structure, such as about 5000 chemical synapses and about 2000 gap junctions at ganglion junctions. It became clear exactly. This research is a laborious process of hand-drawing mapping using electron microscope images and optical character recognition (OCR), which has taken more than 15 years.

Today, advances in image recognition technology have reduced the time it takes to connect the nematodes to one month. By mapping multiple nematodes, research results such as 'The brain's function of processing information from the surrounding environment during mating is consistent in all individuals, even if they are separate bodies with different behavior patterns.' Has been obtained. The importance of Connectome is drawing attention in the scientific community as a database for better understanding of how nerve cells work.

However, the more complex organisms than nematodes, the more difficult it is to map everything in the brain. Especially in humans with about 100 billion nerve cells in the brain alone, it is unclear whether it is universal to all humans just because some nerve cells are matched by multiple people. Mr. Richtmann states, 'If you can map for 100 people, it can be clarified to some extent', but it is not easy to map the amount of information that is said to be 1.4 PB (about 1400 TB) per person.

However, Connectome's research is said to have made significant, albeit partial, progress.

In 2020, we succeeded in mapping 25,000 nerve cells, most of the Drosophila brain. Based on this, we have discovered dozens of new nerve cells and circuits that are said to be activated when Drosophila fly, and this mapping is welcomed as a milestone in Drosophila research.

The Connectome simply maps nerve cells, and there are times when it is not possible to tell from the Connectome alone how much information the nerve cells are transmitting. Still, Lichtmann is convinced that Connectome will be a powerful data source in neuroscience, and says, 'We are excited that innovation is making large-scale Connectome a reality.'

in Science, Posted by log1p_kr