A single mathematical model can explain the pattern of folds seen on the brains of a range of primates, from bush babies to macaques to humans.
at the Federal University of Rio de Janeiro in Brazil and his colleagues have spent years trying to find out whether there is a mathematical description for the crumpled, fractal shape of the cerebral cortex, which is the outer layer of a brain region called the cerebrum.
“The question seems trivial because you can just pick up an MRI image [of a brain] and say this is the shape,” says Mota. “But what if I wanted to compare my description to another [brain]?”
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They have now discovered that some aspects of the mathematics are universal across many primate species.
The researchers focused on how the cortex structure changes at different scales. For instance, their analysis involved zooming in on the fine details of individual folds and, at the other extreme, zooming out and considering only the coarse outline of the cerebral cortex.
The researchers worked with MRI scans of dozens of brains across primate species and analysed them using an algorithm that Mota says is designed to virtually “melt” the structure of the cortex in a series of steps. This means the algorithm removes some of the brain’s fine structure at each step, turning folds and furrows into a smooth surface, until the entire cerebral cortex is largely smooth and featureless.
Then, for each species’ brain, the team arranged this succession of progressively smoother brain shapes on a graph. They found that the graphs for 11 primate species lay on the same kind of line, pointing to a fundamental mathematical similarity in the way the cerebral cortex folds across a wide range of primate species.
To check the algorithm was detecting a real biological signal specific to primates, Mota and his colleagues applied it to scans of walnuts, the surface of which are wrinkled a little like the cerebral cortex, and to bell peppers, which are smooth but have roughly similar dimensions to the primate brain. The graphs for these foodstuffs did not form the same kind of line as the primates brains did, he says.
He in Minneapolis, Minnesota, on 5 March.
at the Transylvanian Institute of Neuroscience in Romania says this is an “amazing addition” to our understanding of how the functions of the brain depend on scale, something that researchers previously only captured with less realistic, two-dimensional analyses. The new approach leaves out some biological details, but the universality it uncovers may point to a kind of biological efficiency that relieves the cortex of having to develop many different folding mechanisms at different scales, he says.
Now, Mota wants to connect his team’s mathematics more closely to how brains change with disease and during the ageing process. The researchers are also studying the largest collection of cetacean brains in Latin America to determine how diving under high pressure may affect the brain’s folding.
