A New Map of the Brain Redraws the Boundaries of Neuroscience
Your brain is a strange three-pound lump in your head that also happens to determine your personality, control your movements, and hold all of your hopes and dreams. Neuroscientists have been mapping the brain for centuries to try to tease apart its inner workings. But people are complicated, and so are brains—intricate bits of biology packed with neurons and axons and all the synapses that tie them together.
That hasn’t stopped neuroscientists from trying. Just like regular maps, brain maps are useful points of reference. Scientists use them to agree on what they’re studying in the first place, say, by pointing to something called the “anterior cingulate cortex” and having other people know what they’re talking about. But over time, better data can refine those maps. So a team of researchers have marshaled a huge amount of brain scan data to create a new, precise brain map, published in Nature today.
This brain-mapping business is not a new endeavor. The first attempts, in the early 20th century, relied on surgeries, brain lesions, and morbid pipe-through-the-head accidents to tease out which part of the brain controlled what (looking at you, Phineas Gage). Neurologists started to pin down areas that, they theorized, were responsible for discrete brain functions: speech, hearing, movement.
Today’s maps are not so comfortingly simple. The new map, created by scientists at Washington University in St. Louis and others, draws in part on the brain’s internal web of connections: how neurons light up together in response to certain stimuli. Based on those areas of co-activity, the map divides the cortex, the layer of tissue on the brain’s exterior, into 360 distinct sections (180 on each hemisphere). “No one’s done this across the whole human brain,” says Matt Glasser, a grad student at WashU and an author of the paper.
These areas aren’t arbitrary. Neuroscientist David Van Essen and his team took MRI and fMRI data from hundreds of subjects and combined the scans to get a better picture of the cortex: how thick it was in certain places, how much insulating myelin there was, and which parts of it lit up when the study’s subjects listened to stories, did math problems, or simply lay in the brain scanner. They carefully lined up the scans and drew boundaries where scans from multiple types of tests seemed to match—and checked previous studies to see whether the areas lined up with ones other scientists had described.
What resulted was a gradient map that sort of looks like a page from an adult coloring book. Some areas play larger roles in seeing, hearing, and feeling, but they aren’t monolithic chunks of brain dedicated exclusively to a certain function. “An analogy I like to use is mapping political subdivisions on the Earth’s surface,” Van Essen says. “They’ve invisible, but they’re key to understanding what’s happening in the world.”
Color-by-cortical area: The study’s map splits up the brain into 360 parcels (180 pairs, one on each hemisphere). It’s based on high-quality data of healthy young adults obtained by the Human Connectome Project.
One big challenge for brain mapping in general, says Robert Savoy, a scientist at Harvard’s Center for Biomedical Imaging, is visualizing all this data as billions of neurons fire. Recording every neuron would take petabytes of data. So where do you draw the line(s)? The new map is an attempt at tackling that challenge. “No one thinks 180 is a perfect number, but it’s a powerful representation of where we are now,” Savoy says. And the map’s creators also acknowledge that it’s a starting point for more detailed research into those sections of the brain. “We’re thinking about it as a strong version 1.0,” Glasser says.
And how neuroscientists represent something as complex as the brain is a bigger debate. Scan the brain at high resolutions (by using an electron microscope, for example), and you get a deluge of data. That fine-grained information is crucial to improve functional brain maps, some scientists argue. Others say that lower-res scans spit out less data, but could offer up a clearer picture of how all the connections fit together.
Wherever neuroscientists settle on this debate, the new map is a stab at imposing some semblance of order on terra incognita. Researchers working off of it can populate it with features, dispute borders, subdivide regions—and, little by little, change the landscape of what science knows about the brain.