Between your ears sits perhaps the most complex piece of biological machinery on the planet: an all-in-one computer, simulator, and creation device that operates out of a squishy, folded grey mass. And scientists aren’t quite sure how it works.
Gül Dölen, assistant professor of neuroscience at the Brain Science Institute at Johns Hopkins, thinks that neuroscientists might need take a step back in order to better understand this organ, which evolved in various forms in nearly every species of animal on Earth. Slicing a few brains apart or taking a few MRIs won’t be enough to get to the bottom of how these organs function. Instead, it might require a comparative approach; the most advanced catalogue ever created. Dölen, who recently made headlines for her work giving MDMA to octopuses, would love to see neuroscientists band together to create a periodic table of the brain. And not just the human brain, but all brains.
She explained her ambitious experiment idea to Gizmodo:
“The periodic table of elements is remarkable. Whenever I look at it, I am amazed and awestruck all over again! Think of it: Just by knowing the number of electrons in the outer shell of an atom, you can deduce physical properties of the element, like is it a gas or a metal, and what’s more, you can use this information to make predictions about unknown properties of elements, and even predict the existence of elements that have yet to be found on Earth. Having the periodic table doesn’t solve all of the puzzles of chemistry, but it certainly gives us the outer border of the puzzle. In neuroscience we don’t have anything like that.”
Dölen compared present-day neuroscience to “somewhere between the ancient Greek’s recognition of four elements and the medieval alchemists trying to change lead into gold.”
Does that sound like hyperbole? Well, consider that neuroscientists can’t even agree on the brain’s most basic information-carrying unit. Perhaps it’s the average electrical field, or maybe it’s action potentials—the electrical output of single brain cells, or neurons. Maybe it’s the combined electrical activity that neurons collect from the other neurons, which they use to determine whether to fire or not. Or maybe its chemicals inside the cells. All of these ideas require different kinds of measurement, like blood-flow monitoring fMRI machines, action potential-detecting electrodes, voltage sensors for measuring the electrical activity before a neuron fires, and protein-detecting systems. Then there’s the blossoming field of genetics, which is also helping determine how the brain might work.
But perhaps each of these different measurements are just part of the many properties that brains have that must be catalogued. They’re equivalent to properties like whether an element is a solid or gas at room temperature, how much energy the atom needs to lose an electron, its radius, atomic weight, and configuration of electrons. But there are many kinds of brains out there. “Right now, our focus on just 5 species (humans, mice, fish, flies, and worms) really limits our ability to see the patterns,” she said. “It’s as if you were trying to figure out the organisation of the periodic table by just looking at hydrogen, carbon, helium, oxygen, and gold.”
Attempts to create general rules for how certain brain properties can predict intelligence often fall apart, Dölen explained. We once thought that brain size could predict intelligence—but sperm whales have much larger brains than humans. Then, we thought ratio of brain size to body weight would predict intelligence—but tree shrews have a larger size-to-weight ratio than people. She pointed out that massive datasets have allowed scientists to create a more accurate picture. For example:
“Suzanna Herculano-Houzel’s lab actually developed a systematic method to count the neurons across over 500 species all across the tree of life. What they found is that, broadly speaking, the number of neurons scales with ‘intelligence,’ and that across different evolutionary lineages, the size of the brain is related either to the size of the neurons or to the number of neurons. So, for example, comparing the human brain to other primates, as the brain gets bigger, the number of neurons increases. But for rodents like mice and rats, as the brain gets bigger, the size of the neurons gets bigger. This huge data set also allows them to look at relationships between neuron number and intelligence, longevity, senility, sociality, etc.”
Dölen compared these insights to the comparative approaches behind the periodic table—once you find the proper patterns and line everything up, the table itself can make predictions. That was perhaps the periodic table’s most profound use: By simply arranging the atoms in a specific way based on their properties, chemist Dmitri Mendeleev was able to accurately the predict the existence and properties of three undiscovered elements based on the holes in his table. Dölen hopes a massive catalogue of the properties of as many brains from as many species as possible, arranged in some pre-determined order, will reveal revolutionary insights about how brains work.
Ultimately, our understanding of brains is limited by our own humanity. “Because we can build mobile phones but mice can’t, we define mice as less intelligent,” said Dölen. “However, compared to mice, humans are morons when it comes to smell intelligence (indeed mice have about 2,000 extra genes for detecting smell compared to humans). Similarly, mantis shrimp have 14 photoreceptors compared to our three, and so are likely to have much greater visual ‘intelligence’ than we do.”
Maybe it’s things that humans don’t always associate with smarts, like sociality, that actually lead to intelligence as we understand it. And maybe it will take lining all these brains up and looking for patterns to make universal rules about how they work.
Such a project would be a huge undertaking, requiring neuroscientists around the world to take a standardised approach to measuring as many details as possible from as many brains as possible. Aside from mass organisation and the incredible amount of grunt work, we have many of the needed techniques already—but, said Dölen, scientists might not even know what measurements are important for creating such a table. Perhaps new insights from compiling the catalogue would lead to new measurement techniques for more specific neural properties. Maybe scientists could even use genetic engineering to genetically modify brains in order to test out hypotheses that arise from the table.
And in an ideal world, the table would even include alien brains to see just how universal those rules can get, said Dölen.
If there really are universal rules guiding how brains develop and function, it will take more than a few measurements of human brains to figure them out. It will take the largest table ever compiled. The impact could be extraordinary, from revolutionising AI to curing brain diseases. “If we had the rules, I can’t even imagine what games we would be able to play,” said Dölen.