*University of California–San Diego, San Diego, California
‡City of Hope Cancer Center, Los Angeles, California
Structure and function are 2 requisite features for developing a map of the human brain. When Brodmann1 defined a map of the cerebral cortex in 1909, he summarized 43 distinct cytoarchitectonic areas of the brain. His work in defining these histologically derived parcels set the framework for understanding the cerebral cortex. Since then, strategies to revise and improve the mapping of the cerebral cortex have been elusive. Even though Brodmann created a map based on postmortem histological characteristics of the cerebrum, he lacked the element of in vivo characterization of function.
Recently, Glasser et al2 established a cortical mapping scheme that uses multiple imaging modalities to characterize distinct parcels of anatomic and functional regions. With the advances of high-quality magnetic resonance images (MRIs), we are now able to noninvasively “peek” into the structure of the brain and measure properties such as myelin content and cortical thickness. The advances in functional MRIs now allow neuroscientists to match a patient’s task-driven function to specific anatomic areas. This new map integrates modern methods of classifying parcels that integrate both functional and anatomic areas of the brain and has been >100 years in the making.
To construct this map, the study coordinators acquired high-quality MRI data of >400 live subjects from the Human Connectome Project. Four different MRI measurements were implemented to help shape the parcels: task-functional MRI, resting-state functional MRI, myelin content, and cortical thickness maps. This new method of parcellation champions the marriage between functional and anatomic structures to develop a new method of defining areas of the cerebrum. In the event of a discrepancy or incongruence between imaging techniques, 2 trained neuroanatomists refereed such differences or faults between the different modalities. Ultimately, all areas of mapping were confirmed to be highly reproducible with a “validation” cohort from the same database. Each parcel is categorized by its auditory, visual, or somatosensory properties, which are the major inputs of the brain. The contrasts of the coloring scheme vary by being task negative or task positive in nature. Of these 180 displayed parcels, 97 are newly identified and have never been described in the literature previously (Figure). The authors envisaged that although there were 180 identified parcels per hemisphere, the likelihood certainly exists that “subparcels” exist within these parcels and should be refined by technological advances in the future.
The implications of a new map of the human cerebrum are profound. This new map can aid neuroscientists and neurosurgeons in their understanding of cognitive and organic disease. Neurosurgeons could integrate this new cortical map to target and treat disease that is specific to the area of clinical concern. Alternatively, neurosurgeons can also use this map to avoid areas of the cerebral cortex that could result in unnecessary neurological deficits from surgical approaches. Cognitive scientists can research patterns of individual, aberrant cortical mapping in cognitive disease such as Alzheimer disease or autistic spectrum disorders. With this new map, diagnosis and management of neurological disease in the near future may be defined with higher degrees of precision and accuracy.
1. Brodmann K. Vergleichende Lokalisationslehre der Grosshirnrinde in ihren Prinzipien dargestellt auf Grund des Zellenbaues: Leipzig, Germany: Barth; 1909.
2. Glasser MF, Coalson TS, Robinson EC, et al. A multi-modal parcellation of human cerebral cortex. Nature. 2016;536(7615):171–178.