A first-of-its-kind study investigating brain connectivity among 130 mammals has revealed something humans may have a hard time believing—the human brain is not superior when compared with others, at least not in terms of connectivity.
Through MRIs and graph theory, researchers from Tel Aviv University have shown that brain connectivity levels are equal in all mammals. Brain connectivity—or the efficiency of information transfer through the neural network—does not depend on the size or structure of the brain.
“In other words, the brains of all mammals, from tiny to large, exhibit equal connectivity, and information travels with the same efficiency within them. Many scientists have assumed that connectivity in the human brain is significantly higher compared with other animals as a possible explanation for the superior functioning of the 'human animal,” said Yaniv Assaf, professor at Tel Aviv University and author of the paper.
Now, Assaf told Laboratory Equipment, he questions whether the human brain really is superior.
“If we take rich language and communication as the main thing that sets us apart from other mammals, there is no reason why the development of this cognitive ability will not fall to the [Conservation of Brain Connectivity] universal law we have found,” Assaf said, referencing the idea that the efficiency of information transfer in the brain's neural network is equal in all mammals.
To arrive at that universal law, the researchers, including professor Yossi Yovel, scanned the brains of 130 mammals, ranging from tiny bats and mice to humans and dolphins. They used diffusion MRI, which uses the diffusion of water molecules to generate contrast and better image white matter in the brain. The imaging technique enabled Assaf and Yovel to reconstruct the neural network in the brains of 100 animals and 32 humans, including the neurons and axons through which information is transferred and the synapses where they meet.
To compare scans of brains that differ in size and structure, the researchers employed network theory, which uses graphs as a representation of symmetric or asymmetric relations between objects. With all brains on level footing, the scientists developed 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.
“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. Information travels from one location to another through the same number of synapses,” Assaf said.
The study results also revealed that the brain has a special compensation mechanism to maintain connectivity: when connectivity between the hemispheres is high, connectivity within each hemisphere is relatively low, and vice versa. Additionally, connectivity compensation varies between not only species, but also individuals within the same species. The brain of a sister bat, for example, could exhibit higher interhemispheric connectivity at the expense of connectivity within the hemispheres while her brother’s brain operates the opposite way.
“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,” Yovel said.
In addition to that research path, the scientists are also looking to extend their research to non-mammal brains, such as birds.