The Simple Origin of Complex Things

A samba group in Niteroi, Rio de Janeiro is what brought physicist Bruno Mota in touch with neuroscience. A casual conversation with researcher Suzana Herculano-Houzel, led him to develop an interest in trying to understand the structure and development of the brain through the fundamental principles and techniques of theoretical physics. Up to that point Mota had been dedicated to cosmology, a field where he researched the origin of something else: the universe.

At the time, he was finishing his doctoral studies in theoretical physics when he discovered that the neuroscientist had just developed a method for counting brain cells and observed some patterns in the way that rodent brains were organized. “I found this observation to be intriguing and we decided to discuss the topic someday. That led to our co-authored paper, where we suggested that these patterns reflected some general universal principals in the organization of mammalian brains,” explained Mota.

He eventually joined Herculano-Houzel’s group as a post-doc fellow in the Comparative Neuroanatomy Laboratory at the Federal University of Rio de Janeiro (UFRJ). It was like taking a sabbatical from cosmology, a field he intended to return to in a year or two. “Five years later, I was still there, and I was hired as a professor at the Institute of Physics based on the research I developed.”

Physicist Bruno Mota

Mota is one of the scientists funded by the Serrapilheira Institute. His research is included in the concept of night science that the institute aims to promote: the kind of science that is somewhere between intuition and data, has great potential for discovery, but is still surrounded by uncertainty. “Everyday science is always concerned with the problems at hand, but it is not until we formally stop working that our more creative stage begins, for example, while biking home, taking a shower or even traveling,” he said. “That is when I say, what about that idea that I didn’t pay much attention to, the one in the corner of my mind?”

Night science is risky science, science that may never actually reach any result. Understanding nature is the priority. Mota’s fondness for this type of basic research was apparent ever since he was an undergrad student in physics and decided to take a course in mathematics, number theory, traditionally known for its theoretical elegance and practical inapplicability. “Mathematicians have a toast they enjoy repeating amongst themselves: to number theory, that it never be useful to anyone!” said the grantee. “However, despite its reputation, I ended up using the discipline in my favorite paper during my doctorate.”

The Origin of the Shape of the Brain

Mota thinks that intuition is the beginning of any science, and his intuition is that complex systems and structures can be understood, for the most part, by means of simplified mathematical models created from general principles. His goal is to produce theories that can be tested and that explain biological structures not only in a specific case, but in all of their diversity.

In more precise terms, Mota studies the origin of the cerebral cortex, a structure found in mammalian brains that is responsible for awareness and other functions. “In some species, like humans, the cortex looks like a wrinkled bedsheet. In others, generally small ones, like rats and primates, the cortex is almost smooth. After reconstructing the cortex surface in mammals, we have been able to show how a careful choice of variables have suggestive numerical patterns, despite the immense diversity and complexity in biological shapes,” he explains.

Based on these patterns and using well established principles of physics, he produced a model that explains why some cortexes are folded and others are smooth, all in function of a single universal rule. When tested, the model shows excellent concordance with observed data from the cortexes of over 60 mammalian species ranging from the mouse to the elephant. The same occurrence is seen in comparisons made between human cortexes and different regions and scales of a single cortex.

“This relation can be used for building a morphological biological clock that can quantify cerebral ageing and might become a prognostic instrument for certain neurodegenerative diseases in the future,” Mota said.
The idea of finding a single universal rule that accounts for the shape of mammalian brains may sound strange. After all, cells make up organs, which make up organisms, and there is no structure more complex and intrinsically interconnected than the cerebral cortex. In humans, for example, the cerebral cortex is made up of tens of billions of neurons connected to each other through trillions of synapses with activities and timeframes that range from milliseconds to decades.

“This does not seem to be a system whose essential properties can be ascertained using basic principles,” Mota acknowledges. “Today, however, thanks to experimental and computational advances, accurate quantitative data about the brain is becoming widely available for the very first time. Now not only can we describe the cerebral cortex in detail, but we can also develop theories that explain its morphology based on simple fundamental principles and produce testable empirical predictions.”

Physics, Neuroscience and Cycling

Bruno Mota found the interface between physics and neuroscience through samba, but another hobby of inspires his creative process: cycling. “Bicycles are slow enough for you to be able to observe your surroundings and fast enough for them to take you to faraway and new places.” It is no coincidence that his folding bicycle is with him at all the scientific events he attends. After a conference in Germany in 2018, he spent a few days biking 350 km to the Baltic Sea in northern Europe before making his way to other meetings in the United Kingdom.

Mota in Orkney, Scotland, when he was biking around the United Kingdom

This interface between two fields of science that a priori are so different, is uncommon. Conducting research in theoretical biology in ways that are analogous to doing so in physics is still rather unusual in the world and, according to Mota, “a little subversive.” “Even abroad, most physicists, mathematicians and computer scientists that work in the field contribute experimental techniques or image and data analysis.” In Mota’s view, these fields are closer that they seem. “Both neuroscience and cosmology deal with the simple origin of complex things.”