Written By

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Martin A. Samuels, MD, DSc(hon), MACP, FAAN, FRCP, FANA
Co-Editor, Neurology Section, Scientific American Medicine
Co-Editor, Scientific American Neurology
Chair, Department of Neurology, Brigham and Women’s Hospital
Miriam Sydney Joseph Professor of Neurology, Harvard Medical School

In the July 20 issue of Nature, a new map of the human brain was published by Matthew Glasser, Ph.D. and David Van Essen, Ph.D. from Washington University in St. Louis and their colleagues at other institutions. It is a multi-modal parcellation of the human cerebral cortex using information from structural and functional MRI collected from 210 subjects in the Human Connectome Project. They have mapped 180 areas in each hemisphere. Even more may emerge as the work is extended.

It is useful to put this contribution in the context of the age-old dialectic contrasting two views of the way in which the nervous system works: the localization concept versus the holistic concept.

Localization was championed by Franz Joseph Gall, who argued that certain areas of the brain were specialized for particular functions. This led to the now discredited theory of phrenology whereby these areas were reflected by the shape of the overlying skull. Paul Broca’s famous case of Lebourgne, published in 1862, strongly supported the localization theory; Korbinian Brodman, at the end of the nineteenth century, created his now-famous map consisting of 52 cortical areas. However, in the mid-portion of the 19th century, the holistic theory was championed by Pierre Flourens, who essentially argued that the brain was much like the liver and functioned in an integrative manner.

In the 20th century, the localization theory clearly prevailed, and virtually all students of medicine were taught the “neurological method,” by which was meant anatomic localization was the cornerstone of correct diagnosis, which would then inform therapy. Many of the core tenets of localization, such as language belonging mainly in the left hemisphere, vision in the occipital lobes, hearing in the temporal lobe, motor function in the posterior frontal lobes, sensation in the parietal lobes, have stood the test of time with regard to mundane neurological diagnosis. However, complex functions such as attention, praxis, cognition, and other functions have eluded static anatomical localization. The advent of exquisite structural and then functional imaging, using magnetic resonance has stimulated a recrudescence of some aspects the holistic theory in its more modern guise of network theory.

The new map of the human cortex represents a new synthesis of the old thesis (localization) and antithesis (holistic) views of the function of the brain. Perhaps the neurologist of the future will work with this new map in a way analogous to the Brodman map of the prior generations to understand better how the brain works and even open a window into the nature of consciousness itself.

 


The full article by Glasser, MF, Coalson, TS, et al. can be found at  http://www.nature.com/nature/journal/vaop/ncurrent/full/nature18933.html