In Retrospect: Brodmann's Brain

OPINION NATURE|Vol 461|15 October 2009 In Retrospect: Brodmann’s brain map A classic neurology text written 100 years ago still provides the core principles for linking the anatomy of the cerebral cortex to its functions today, explains Jacopo Annese. Localisation in the Cerebral Cortex Using a microscope designed for the purpose, discuss these towards the end. Some of his by Korbinian Brodmann he undertook meticulous examinations of peers were more forthright about labelling First published 1909 (in German). cortical tissue from the brains of humans and cortical regions according to function, notably many other mammals, the results of which the Australian-born neurologist A. W. Camp- enabled him to construct his map of the human bell, who used clinical evidence with results The development of advanced magnetic cortex. The map looks simple, yet the book from physiological experiments and anatomi- resonance imaging techniques over the past makes it clear it is based on a monumental cal analysis to make his case. Still, Brodmann’s 30 years has heralded today’s ‘golden age’ of analytical effort. His exquisite powers of obser- objective approach has ensured that his maps human brain mapping. Yet in the quest to chart vation and great attention to detail transform have endured, eclipsing others of the time such structural and functional subdivisions in the for the reader the tedium of scientific annota- as Campbell’s. brain, and in the cerebral cortex in particular, tion into an exercise in anatomical voyeurism. Another of Brodmann’s long-lasting the first quarter of the twentieth century was achievements documented in the book is his at least as momentous. defence of the accepted view that the cerebral At the forefront of that pioneering effort cortex is divided into six fundamental layers, was a German physician who is still revered by a view shared by some — but not all — neu- brain scientists today, but whose seminal book rologists of the time. Brodmann’s rationale on cortical anatomy is read by few. Korbinian was based on his own interpretation of devel- Brodmann’s Localisation in the Cerebral Cor- opmental and anatomical evidence that was tex, published 100 years ago, details his system potentially disputable, but his strong stance LONDON LIBRARY, WELLCOME for subdividing the cortex into 52 areas, each quieted the debate and it has been universally signified by a number, on the basis of their accepted with time. Indeed, the only valid crit- cell type and laminar structure. It is a classic icism of Localisation in the Cerebral Cortex is of neurology: Brodmann’s numbers are still that Brodmann failed to provide a clear photo- used to indicate the location and function of graphic record of the cortical areas he was clas- cortical areas, and his trademark drawings sifying. This technical drawback has made it of the human brain are reprinted wherever hard to challenge or invalidate his conclusions neuroscience is taught or practised. Person- about the way the cortex is subdivided, and has ally, I have re-read the book carefully because therefore preserved the impact of his map. my laboratory is engaged in producing a map Brodmann’s enterprise has stood up against of the cortical surface based on anatomical what we have learned recently about brain criteria, just like Brodmann, but using mod- architecture from modern neuroimaging ern digital technology (see http://thebrainob- techniques remarkably well. His approach servatory.ucsd.edu/brodmann.html). remains convincing because it is based on a In Brodmann’s era, most cortical mapping Two of Brodmann’s classic drawings from 1909. small number of unambiguous postulations took place in pathological laboratories that and a deep personal involvement with the were linked to mental asylums and overseen The descriptions alone mark out the book as a data. The arsenal of chemical and molecular by government bodies. But his effort started in classic, but it is well worth reading today for techniques and digital-microscopy tools now an independent institute — the Neurobiologi- several reasons. It touches on issues that are at our disposal gives us far greater power to cal Laboratory in Berlin, supported and run by highly relevant to modern neuroscience, start- analyse brain structure than Brodmann had. the neurologists Oskar Vogt and Cécile Vogt. ing with the idea that specific physiological Yet future projects should seek to learn from The Vogts were mainly concerned with the functions in the cerebral cortex depend on spe- his impressive methods of synthesis rather architecture of myelinated nerve fibres, and cific histological structure and connectivity. than focusing solely on surpassing his meth- how different areas of the cortex were linked Although Brodmann’s numbers are widely ods. Whatever a new microscopic map of the to specific physiological functions, which used to link brain regions with function cerebral cortex may look like, it will doubt- they tested by stimulating the brains of ani- — area 4 for the primary motor cortex, for less be based on the principles that Brodmann mals. They brought in Brodmann to carry out example — you get the sense from the book defended a century ago. ■ a topographical analysis of the human cerebral that he did not want to tarnish his mapping Jacopo Annese is director of The Brain cortex based exclusively on its cellular struc- effort by making predictions about func- Observatory at the University of California, ture (the cytoarchitecture), using a staining tional properties that might not stand the San Diego, California 92121, USA. method developed by their contemporary, test of time. He reminded his readers that his e-mail: jannese@ucsd.edu Franz Nissl. investigation was based “exclusively on ana- The task was theoretically straightforward, tomical features”, rather than on physiologi- See online at go.nature.com/phyLwm for more on yet it occupied Brodmann for almost a decade. cal or clinical approaches, although he does neuroscience. 884 © 2009 Macmillan Publishers Limited. All rights reserved.

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