MRI of the brains of 130 species of mammals, including humans, indicates the same connectivity in all of them

Researchers from Tel Aviv University, led by Professor Yaniv Assaf from the School of Neurobiology, Biochemistry and Biophysics and the Sagol School of Neuroscience and Professor Yossi Yovel from the School of Zoology, the Sagol School of Neuroscience and the Museum Steinhardt of Natural History, conducted a pioneering study, the first of its kind in the world: advanced diffusion MRI scans of mammalian brains representing about 130 species, designed to investigate brain connectivity. The intriguing results, which contradict widespread conjecture, revealed that levels of brain connectivity are the same in all mammals, including humans.

Prof. Assaf: “We found that brain connectivity (that is, the efficiency of information transfer through the neural network) does not depend on the size or structure of any specific brain. In other words, everyone’s brain Mammals, from small mice to humans to large bulls and dolphins: exhibit equal connectivity and information travels just as efficiently within them. We also found that the brain preserves this balance through a special compensation mechanism: when connectivity between hemispheres is high, connectivity within each hemisphere is relatively low, and vice versa. ”

Participants included researchers from the Kimron Veterinary Institute in Beit Dagan, the Blavatnik School of Computer Science at TAU, and the Technion School of Medicine. The article was published in Nature Neuroscience in June 2020.

Professor Assaf explains: “Brain connectivity is a central feature, critical to brain function. Many scientists have assumed that connectivity in the human brain is significantly higher compared to other animals, as a possible explanation for the superior functioning of the brain.” “. On the other hand, according to Professor Yovel,” We know that key characteristics are preserved throughout the evolutionary process. Thus, for example, all mammals gave four limbs. In this project we wish to explore the possibility that brain connectivity is a key characteristic of this type: maintained in all mammals, regardless of their brain size or structure. For this we use advanced research tools. ”

Size doesn’t count

The project started with advanced diffusion MRI scans of the brains of some 130 mammals, each representing a different species (it should be noted that all brains were removed from dead animals and no animals were sacrificed for the purposes of this study). The brains, obtained from the Kimron Veterinary Institute, represented a wide range of mammals, from small bats weighing 10 grams to dolphins weighing hundreds of kilograms. Since the brains of approximately 100 of these mammals had never been scanned by MRI before, the project generated a novel and globally unique database. The brains of 32 living humans were also scanned in the same way. The unique technology, which detects white matter in the brain, allowed researchers to reconstruct the neural network: the neurons and their axons (nerve fibers) through which information is transferred, and the synapses (junctions) where they meet .

The next challenge was to compare the scans of different types of animals, whose brains vary greatly in size and / or structure. For this purpose, the researchers used tools from Network Theory, a branch of mathematics that allowed them to create and apply a uniform indicator of brain conductivity: the number of synopses a message must cross to get from one place to another in the neural network. .

Professor Assaf explains: “The brain of a mammal consists of two hemispheres connected to each other by a set of neural fibers (axons) that transfer information. For each brain we scan we measure four connectivity meters: connectivity in each hemisphere (intrahemispheric connections) , connectivity between the two hemispheres (interhemispheric) and general connectivity. We found that general brain connectivity remains the same for all mammals, large or small, including humans. In other words: information travels from one place to another to across the same number of synopses. However, it should be clarified that different brains use different strategies to preserve this equal measure of overall connectivity: some exhibit strong interhemispheric connectivity and weaker connectivity within hemispheres, while others show the opposite. ”

Professor Yovel describes another interesting discovery: “We found that variations in connectivity compensation characterize not only different species but also different individuals within the same species. In other words, the brains of some rats, bats or humans exhibit greater connectivity. It would be fascinating to hypothesize how different types of connectivity

brain can affect various cognitive functions or human abilities such as sports, music or mathematics. It will be addressed in our future research. ”

A new universal law

Professor Assaf concludes: “Our study revealed a universal Law: Conservation of brain connectivity. This Law denotes that the efficiency of information transfer in the brain’s neural network is the same in all mammals, including humans. We also discovered a compensation mechanism that balances connectivity in all mammalian brains. This mechanism ensures that high connectivity in a specific area of ​​the brain, possibly manifested through some special talent (eg, sports or music), is always counteracted by relatively low connectivity elsewhere in the brain, he will investigate how the brain compensates for the enhanced connectivity associated with specific learning processes and capabilities. “

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