MRI scans of the brains of 130 mammals, including humans, indicate equal connectivity

Date:
July 20, 2020
Source:
American Friends of Tel Aviv University
Summary:
Researchers conducted a first-of-its-kind study designed to
investigate brain connectivity in 130 mammalian species. The
intriguing results, contradicting widespread conjectures, revealed
that brain connectivity levels are equal in all mammals, including
humans.



FULL STORY ========================================================================== Researchers at Tel Aviv University, led by Prof. Yaniv Assaf of the
School of Neurobiology, Biochemistry and Biophysics and the Sagol
School of Neuroscience and Prof. Yossi Yovel of the School of Zoology,
the Sagol School of Neuroscience, and the Steinhardt Museum of Natural
History, conducted a first- of-its-kind study designed to investigate
brain connectivity in 130 mammalian species. The intriguing results, contradicting widespread conjectures, revealed that brain connectivity
levels are equal in all mammals, including humans.


==========================================================================
"We discovered that brain connectivity -- namely the efficiency of
information transfer through the neural network -- does not depend on
either the size or structure of any specific brain," says Prof. Assaf. "In other words, the brains of all mammals, from tiny mice through humans to
large bulls and dolphins, exhibit equal connectivity, and information
travels with the same efficiency within them. We also found that the
brain preserves this balance via a special compensation mechanism: when connectivity between the 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 School
of Computer Science at TAU and the Technion's Faculty of Medicine. The
paper was published in Nature Neuroscience on June 8.

"Brain connectivity is a central feature, critical to the functioning
of the brain," Prof. Assaf explains. "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 'human animal.'" On the other hand, according to Prof. Yovel,
"We know that key features are conserved throughout the evolutionary
process. Thus, for example, all mammals have four limbs. In this project
we wished to explore the possibility that brain connectivity may be a key feature of this kind -- maintained in all mammals regardless of their
size or brain structure. To this end we used advanced research tools."
The project began with advanced diffusion MRI scans of the brains of
about 130 mammals, each representing a different species. (All of the
brains were removed from dead animals, and no animals were euthanized
for the purposes of this study.) The brains, obtained from the Kimron Veterinary Institute, represented a very wide range of mammals -- from
tiny bats weighing 10 grams to dolphins whose weight can reach hundreds
of kilograms. Since the brains of about 100 of these mammals had never
been MRI-scanned 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 the white matter in
the brain, enabled the 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 comparing the scans of different types of
animals, whose brains vary greatly in size and/or structure. For this
purpose the researchers employed tools from Network Theory, a branch
of mathematics that enabled them to create and apply a uniform gauge of
brain conductivity: the number of synopses a message must cross to get
from one location to another in the neural network.

"A mammal's brain consists of two hemispheres connected to each other by
a set of neural fibers (axons) that transfer information," Prof. Assaf explains. "For every brain we scanned, we measured four connectivity
gages: connectivity in each hemisphere (intrahemispheric connections), connectivity between the two hemispheres (interhemispheric), and overall connectivity. We discovered that overall brain connectivity remains the
same for all mammals, large or small, including humans. In other words, information travels from one location to another through the same number
of synapses. It must be said, however, that different brains use different strategies to preserve this equal measure of overall connectivity: some
exhibit strong interhemispheric connectivity and weaker connectivity
within the hemispheres, while others display the opposite." Prof. 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," he says. "In
other words, the brains of some rats, bats, or humans exhibit higher interhemispheric connectivity at the expense of connectivity within
the hemispheres, and the other way around -- compared to others of
the same species. It would be fascinating to hypothesize how different
types of brain connectivity may affect various cognitive functions or
human capabilities such as sports, music or math. Such questions will be addressed in our future research." "Our study revealed a universal law: Conservation of Brain Connectivity," Prof.

Assaf concludes. "This law denotes that the efficiency of information
transfer in the brain's neural network is equal in all mammals,
including humans. We also discovered a compensation mechanism which
balances the connectivity in every mammalian brain. This mechanism
ensures that high connectivity in a specific area of the brain, possibly manifested through some special talent (e.g. sports or music) is always countered by relatively low connectivity in another part of the brain. In future projects we will investigate how the brain compensates for the
enhanced connectivity associated with specific capabilities and learning processes."

========================================================================== Story Source: Materials provided by
American_Friends_of_Tel_Aviv_University. Note: Content may be edited
for style and length.


========================================================================== Journal Reference:
1. Yaniv Assaf, Arieli Bouznach, Omri Zomet, Assaf Marom, Yossi Yovel.

Conservation of brain connectivity and wiring across the mammalian
class.

Nature Neuroscience, 2020; 23 (7): 805 DOI:
10.1038/s41593-020-0641-7 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/07/200720112216.htm

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