Researchers at Washington University School of Medicine in St. Louis have developed a new map of the landscape of the cerebral cortex – the outermost layer of the brain and the dominant structure involved in sensory perception and attention, as well as distinctly human functions such as language, tool use and abstract thinking.
With the features of a typical brain demarcated in painstaking detail, the new map helps researchers studying brain disorders such as autism, schizophrenia, dementia and epilepsy. Scientists will be able to use it in deciphering the workings of the healthy brain and the affected one.
The work was published July 20 in Nature.
The researchers drew the map based on data generated by the Human Connectome Project, a five-year, multimillion dollar study led by David Van Essen, the senior author on the paper, and involving a consortium that includes the University of Minnesota and Oxford University. The Human Connectome Project used a powerful, custom-built MRI machine to map the brains of 1,200 young adults. This study complements the Human Connectome Project by carefully delineating the brain regions so that their connections can be more accurately mapped.
The new map divides both the left and right cerebral hemispheres into 180 areas based on physical differences (such as the thickness of the cortex), functional distinctions (such as which areas respond to language stimuli), and differences in the connections of the areas. Brain cartography is not simple as much of the brain looks superficially the same. The map is more akin to a map showing state borders than topographic features; the most important divisions are invisible from the sky but extremely important all the same.
“The brain is not like a computer that can support any operating system and run any software,” said Van Essen. “Instead, the software – how the brain works – is intimately correlated with the brain’s structure – its hardware, so to speak. If you want to find out what the brain can do, you have to understand how it is organized and wired.”
The researchers mapped the cortex, a layer of neural tissue that encases the rest of the brain like a crumpled sheet of paper. The cortex is important for sensation, attention, memory, perception, thought, language and consciousness.
To make this map, Glasser, Van Essen and colleagues pooled data from 210 healthy young adults of both sexes. The researchers combined measures of the thickness of the cortex and the amount of insulation around neuronal cables, with MRI scans of the resting brain and of the brain performing simple tasks, such as listening to a story.
“We ended up with 180 areas in each hemisphere, but we don’t expect that to be the final number,” Glasser said. However, he said the team identified a patch of cortex that probably could be subdivided, but could not draw borders with the current data and techniques.
The results are a precise map with unusually crisp borders and an algorithm capable of locating the areas in individual brains, even though each individual is unique in terms of the pattern of cortical folds and in the size and shape of areas on the cortical map.
“In the past, it was not always clear whether the results from two separate neuroimaging studies referred to the same area or not,” Glasser said. By using the new map and alignment algorithm, results of separate studies could be more accurately compared.
Better individual maps of the brain could be very useful. Neurosurgeons at Washington University already use less detailed individual brain maps when preparing for surgery to avoid damaging the most important areas, such as those involved in language or motor function.
Individual brain maps also could guide treatment for neurological or psychiatric illnesses. Different types of dementia, for example, are characterized by degeneration in different areas of the brain. Clinicians could use the individual maps to personalize treatment, based on the areas affected, or to monitor response to treatment.
Like cartographers of old, brain cartographers primarily are providing a tool for others to use in exploration and discovery.
“We were able to persuade Nature to put online almost 200 extra pages of detailed information on each of the 180 regions as well as all of the algorithms we used to align the brains and create the map,” Van Essen said. “We think it will serve the scientific community best if they can dive down and get these maps onto their computer screens and explore as they see fit.”