The number of separate domains recognized in the human cortex has doubled, thanks to a newly developed map based on functional MRI brain scans.
Previous studies charted 83 brain regions in each hemisphere of the brain – for example, Broca’s Area, which is thought to be responsible for speech production. The mapping of those regions was typically based on just one measure, such as examining tissue samples under a microscope. The boundaries of the regions were often uncertain.
“The situation is analogous to astronomy, where ground-based telescopes produced relatively blurry images of the sky before the advent of adaptive optics and space telescopes,” study lead author Matthew Glasser, a researcher at Washington University in St. Louis, said in a news release.
To produce a sharper image, Glasser and colleagues at seven research centers conducted fMRI scans on 210 healthy study participants. They looked for similarities and differences in cortical architecture, activity, connectivity and topography – and then fed those readings into software that produced a map of regions with similar qualities.
That map identified 97 additional cortex areas per hemisphere, for a total of 180. The analysis was verified by checking the map against an independent set of readings from 210 other participants.
Some of the brain scans were conducted while the participants were performing tasks. One of the newly identified regions, known as Area 55b, appears to be more active when a person listens to a story. But many of the new regions have not yet been linked to specific functions.
Senior author David Van Essen, a colleague of Glasser’s at Washington University, said some of the regions may turn out to have further subdivisions, or work together as parts of larger functional regions.
In a Nature commentary, neuroscientists B.T. Thomas Yeo and Simon Eickhoff said the map would serve as “a reference atlas that will allow those researching brain structure, function and connectivity to work within a common, systems-neuroscience framework.”
But Glasser emphasized that this wouldn’t be the be-all and end-all of brain maps. For example, Seattle’s Allen Institute for Brain Science has been working on a series of maps that link brain regions with gene expression.
“The ability to discriminate individual differences in the location, size and topology of cortical areas from their differences in their activity or connectivity should facilitate understanding of how each property is related to behavior and genetic underpinnings,” Glasser said.
In addition to Glasser and Van Essen, the authors of “A Multi-Modal Parcellation of Human Cerebral Cortex” include Timothy Coalson, Emma Robinson, Carl Hacker, John Harwell, Essa Yacoub, Kamil Ugurbil, Jesper Andersson, Christian Beckmann, Mark Jenkinson and Stephen Smith.