The human brain is a complex structure, full of different regions that connect to each other in different ways. For centuries, scientists have tried to map out these areas in an attempt to better understand how the brain works. Now, researchers have published a new brain "atlas" that includes nearly 100 previously unmapped regions.
The idea is to offer neuroscientists a more precise way of pinpointing areas of the brain, which could help with understanding both how the brain works and what goes wrong in brain disorders.
The new map shows areas associated with different tasks in different colours—blue for vision and red for hearing, for example.
But David Van Essen, a neuroscientist at Washington University who was involved in the research, explained that the connections between areas are just as important. "What is also very clear, and consistent with what we expected from previous studies, is that there's not a sharp dividing line where suddenly red turns to green or blue," he said. "Rather, there are gradual transitions, indicating that there's intermixing and coordination among different sensory modalities and cognitive domains."
In other words, there are still questions to be asked about how much each cortical area is specialised for a specific role, and how much they are part of a broader coordinated network.
Van Essen told Motherboard that he has personally been working as a "cortical cartographer" since the 70s, but recent technological advances made the new map possible.
In their paper published on Wednesday in the journal Nature, researchers describe 180 areas in each hemisphere of the human brain's cerebral cortex—the outer layer of "grey matter" that's known to play a vital role in everything from motor function to language and logical reasoning.
"Our understanding, even with this new paper that's come out, is not the equivalent of a Google map"
Van Essen compared the endeavour to mapping the Earth, but while the physical folds of the brain might be comparable to the Earth's topology, he explained that the areas identified in the new brain map are more analogous to the "political subdivisions of the Earth's surface."
"They are based not on the folds of the cortex per se, but rather on the intricate interactions, communications, and connections between the many billions of neurons that make up the cerebral cortex," he said.
So how did they do it? The researchers, led by Washington University's Matthew Glasser, made their maps by analysing several types of imaging data from MRI scans of 210 people, which was collected through a consortium called the Human Connectome Project.
In a comment piece also published in Nature, engineer B T Thomas Yeo and neuroscientist Simon Eickhoff write that the key difference between this new map and previous attempts is that the researchers looked at several features of the brain, rather than just one, to draw their dividing lines. For example, the MRI scans looked at features including the thickness of the cortex and blood flow in a resting state and in response to different task.
To check that their findings were applicable across different people's brains, the researchers then used machine learning algorithms based on their maps to identify the brain areas in a separate set of 210 people. This shows that the maps can be used despite individual variation.
It's down to the broader neuroscience community to make use of the map; the researchers hope that their peers will use their new mapping paradigm to guide and describe their own findings.
Van Essen said the project had so far met with interest and enthusiasm. "We're reasonably confident that many neuroscientists are champing at the bit to go at this," he said.
That said, it's worth noting that our knowledge of the human brain is by no means complete, and Van Essen was open about the limitations of this new map.
"Our aspiration is to make the best possible maps that we can, but we have to be honest in saying our understanding, even with this new paper that's come out, is not the equivalent of a Google map," he said. "We don't have the ability to navigate the cerebral cortex down to the level of individual neurons or even tiny patches."
He reckons the new brain classification is comparable to something like a 19th century map of the world.