Brain connectivity equal among mammals, groundbreaking study finds

The study upends prevailing scientific consensus on brain connectivity levels.

An image of the human brain (photo credit: REUTERS)
An image of the human brain
(photo credit: REUTERS)
A new first-of-its-kind study from Tel Aviv University has revealed that brain connectivity is equal in all mammals, humans included, debunking widespread consensus among scholars.
The study – led by Prof. Yaniv Assaf of Tel Aviv University's School of Neurobiology, Biochemistry and Biophysics and the Sagol School of Neuroscience; and Prof. Yossi Yovel of the School of Zoology, Sagol School of Neuroscience and Steinhardt Museum of Natural History – utilized advanced MRI brain scans on mammals from 130 different species in order to monitor brain connectivity, which is how efficiently information travels throughout the brain.
Previously, the prevailing scientific consensus was that brain connectivity would be in some way dependent on the size or structure of the brain. As a result, brain connectivity in human brains was assumed to be at a higher level compared to other mammals. However, this study, published in the academic journal Nature Neuroscience, reveals otherwise.
"We discovered that brain connectivity does not depend on either the size or structure of any specific brain. 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," Assaf said in a statement.
"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."
The study examined brains from a variety of different species, including the 10 gram brains of bats to the far larger and heavier brains of dolphins. Out of all the species examined, 100 of them had never had their brains scanned before by an MRI, making this a first for researchers around the world.
Comparing the scans of animals with radically different brain sizes and structures was a great challenge, but the researchers were able to use mathematical tools to create a uniform brain conductivity gauge.
"A mammal's brain consists of two hemispheres connected to each other by a set of neural fibers (axons) that transfer information," Assaf explained.
"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 synopses. It must be clarified, 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."
Assaf now believes that the study has revealed a new universal law in the field, the conservation of brain connectivity, which states that information is transferred through the brain at the same efficiency through all mammals.
"We also discovered a compensation mechanism which balances the connectivity in every mammalian brain," Assaf added. "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."