Neuroscientists working on the Human Connectome Project have compiled the most accurate map yet of the human cerebral cortex. The researchers identified 180 distinct areas of the brain's outer layer — effectively doubling the previous number of known regions. Researchers have mapped 180 areas of the human cerebral cortex, of which 97 are completely new to science. (Image: Matthew F. Glasser, David C. Van Essen)
The new map, compiled by David Van Essen and Matthew Glasser of Washington University in St Louis — with the help of colleagues from several other institutions — confirmed the existence of 83 previously known regions. The team also identified 97 new areas of the human cerebral cortex — the outer part of the brain responsible for sensory and motor processing, language and logical reasoning. Published in Nature, the updated map will serve as a new reference atlas to assist in the ongoing study of brain structure, function and connectivity.
Brain patterns observed while participants were listening to stories. (Image: Matthew F. Glasser, David C. Van Essen)
Geographers and neuroscientists share something in common: They both need maps to do their work and improve their understanding of what they're looking at. When it comes to brain science, researchers need a map that shows the brain's major subdivisions, known as cortical areas. Each of these areas is responsible for a particular cognitive function, such as touch, personality and planning, and many of them work in conjunction with other areas.
The trouble is, creating these maps is easier said than done. Every location of the brain contains an enormous set of features, from cellular structure and the density of proteins, to various neurotransmitter molecules and long-range connections. Scientists have struggled to define many of these features, resulting in a fairly hazy and often ambiguous map of the cerebral cortex.
Brain scan showing a map of myelin content, a sheath that surrounds some nerve cells. (Image: Matthew F. Glasser, David C. Van Essen)
Previous studies lacked the tools, and hence the proper resolution, required to create a map with the required level of detail. But according to study lead author Matthew Glasser, a fortunate set of circumstances came together to make it possible.
"[The Human Connectome Project] started back in 2010 and the National Institutes of Health gave us two years to work on improving the MRI acquisition methods and the data analysis methods," he told Gizmodo. "That allowed us to get much higher quality data than was typically available." The project also brought together neuroimaging experts from around the world to work on these issues.
The tools, methods and software used by the researchers were also unique, including the use of multiple measures, rather than a single measure, of architecture, function, connectivity and topographic maps. Finally, the team trained a learning algorithm to recognise the "fingerprints" of the various areas across all measures. That algorithm was able to process the trove of incoming data and identify regions that would normally be invisible to the researchers.
The 180 areas identified in both left and right hemispheres. (Matthew F. Glasser et al., 2016/Nature)
The end result was a highly accurate, high-resolution map of the cerebral cortex's microstructural architecture, connectivity and function. The researchers gave the map a name worthy of its stature: The Human Connectome Project Multi-Modal Parcellation version 1.0, or HCP-MMP1.0 for short.
Of the 180 regions mapped, some performed an obvious function, while others evaded explanation. For example, area 55b is involved in language tasks, according to Glasser. In about 90 per cent of healthy young adults, this region has a typical pattern of relationships with its neighbours. But in some small fraction of the 210 study participants, it displayed different patterns, including a surprising association with areas involved in eye movements.
"Another interesting area is POS2. This is an area that had not previously been mapped before neuroanatomically," said Glasser. "We don't yet know what it is doing, but given its unique pattern, it will likely be something very specialised."
In terms of actual applications, the updated map will be used by neuroimaging experts to help them understand where they are in the brain. It will also improve our understanding of how the brain works. And as Glasser pointed out, it could also be used by surgeons during the planning stage, where brain areas could be mapped ahead of an operation.
Looking ahead, Glasser and his team are focusing on helping the community use the new map and some of the improved brain imaging methods developed as part of the project. They're also hoping to look at the human connectome, that is, the many pathways that underlie brain function and behaviour, to study the effects of ageing.