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Confusing Cortical Columns,’’ by GENETICS COMMENTARY. For the article ‘‘Confusing cortical columns,’’ by GENETICS. For the article ‘‘Fine structure mapping of a gene-rich Pasko Rakic, which appeared in issue 34, August 26, 2008, of region of wheat carrying Ph1, a suppressor of crossing over Proc Natl Acad Sci USA (105:12099–12100; first published between homoeologous chromosomes,’’ by Gaganpreet K. August 20, 2008; 10.1073͞pnas.0807271105), the authors note Sidhu, Sachin Rustgi, Mustafa N. Shafqat, Diter von Wettstein, that, due to printer’s errors, three references were omitted and and Kulvinder S. Gill, which appeared in issue 15, April 15, 2008, a phrase appeared incorrectly. On page 12099, left column, of Proc Natl Acad Sci USA (105:5815–5820; first published April second paragraph, line 11, ‘‘(e.g., ref. 2)’’ should appear as ‘‘(e.g., 8, 2008; 10.1073͞pnas.0800931105), the authors note that ‘‘a part refs. 2, 22, and 23).’’ Also on page 12099, right column, line 6, of our Fig. 1 was reproduced from figure 1 of the paper by Simon ‘‘single receptive field’’ should instead read: ‘‘single modalities in Griffiths et al. [Griffiths S, et al. (2006) Nature 439:749–752]. In the receptive field.’’ Finally, on page 12100, center column, line our paper we neglected to reference this figure as adapted from 21, ‘‘(15, 19)’’ should appear as ‘‘(15, 24)’’; and in line 25, the original work.’’ ‘‘(19–21)’’ should appear as ‘‘(21–24).’’ In addition to these ͞ ͞ ͞ ͞ errors, the authors note that in ref. 3, the author names www.pnas.org cgi doi 10.1073 pnas.0808507105 ‘‘Herculano-Housel S, Collins CE, Wang P, Kaas J’’ should have appeared as ‘‘Herculano-Houzel S, Collins CE, Wong P, Kaas JH, Lent R.’’ The corrected and omitted references appear below. 3. Herculano-Houzel S, Collins CE, Wong P, Kaas JH, Lent R (2008) The basic nonuniformity of the cerebral cortex. Proc Natl Acad Sci USA 105:12593–12598. 22. Purves D, Riddle DR, LaMantia AS (1992) Iterated patterns of brain circuitry (or how the cortex gets its spots). Trends Neurosci 15:362–368. 23. Horton JC, Adams DL (2005) The cortical column: A structure without a function. Philos Trans R Soc London Ser B 360:837–862. 24. Rakic P (1995) A small step for the cell, a giant leap for mankind: A hypothesis of neocortical expansion during evolution. Trends Neurosci 18:383–388. www.pnas.org͞cgi͞doi͞10.1073͞pnas.0808511105 CELL BIOLOGY. For the article ‘‘Dual-color superresolution imag- ing of genetically expressed probes within individual adhesion complexes,’’ by Hari Shroff, Catherine G. Galbraith, James A. Galbraith, Helen White, Jennifer Gillette, Scott Olenych, Mi- chael W. Davidson, and Eric Betzig, which appeared in issue 51, December 18, 2007, of Proc Natl Acad Sci USA (104:20308– 20313; first published December 12, 2007; 10.1073͞ pnas.0710517105), the authors note that on page 20312, right column, in Materials and Methods, under Sample Preparation, line 4, ‘‘Cell Line Nucleofector Kit SF’’ should have appeared as ‘‘Cell Line Nucleofector Kit SE.’’ www.pnas.org͞cgi͞doi͞10.1073͞pnas.0808557105 15220 ͉ www.pnas.org Downloaded by guest on October 2, 2021 COMMENTARY Confusing cortical columns Pasko Rakic* Department of Neurobiology and Kavli Institute for Neuroscience, Yale University School of Medicine, New Haven, CT 06510 he late developmental neurobi- phers who liked the idea that the differ- (5) discovered that the neurons ar- ologist, and a member of the ence between animals and human are ranged vertically (or radially in the National Academy of Sciences, just quantitative. It also provided the sci- convoluted cerebrum) in the form of Victor Hamburger told me dur- entific basis of the so-called ‘‘tabula rasa columns spanning the width of the pri- Ting one of our discussions about the hypothesis’’ of cortical development, mate somatosensory cortex respond to a distinction between boring data and ex- which assumes that all cytoarchitectonic single receptive field at the periphery. citing concepts, ‘‘one can spend an en- areas are specified from the initially ho- This, and subsequent research by many tire lifetime correcting a flawed paper mogeneous and equipotential cortex by others, has shown that the cortical col- published in reputable journal and still input from the periphery. umns consist of an array of iterative loose the battle if people like the basic This is why the article by Herculano- neuronal groups (also called modules) idea’’ (V. Hamburger, personal commu- Housel et al. (3) in this issue of PNAS that extend radially across cellular layers nication). An example of the longevity serves a useful purpose, even though it VI to II with layer I at the top (6–10). of basically incorrect information is the does not report any unexpected results. The neurons within a given column are phenomenon of ‘‘The basic uniformity Using a state-of-the-art unbiased stere- stereotypically interconnected in the ver- in structure of the neocortex,’’ published ology method, the authors show con- tical dimension, share extrinsic connec- in 1980 by Rockel, Hiorns, and Powell vincingly that the density of neurons in tivity, and hence act as basic functional (1). This highly influential paper had the neocortex varies as much as three units subserving a set of common static obvious problems at almost every level: times even among the highly related pri- and dynamic cortical operations that The authors selected an arbitrary 30- mate species. The results from the two include not only sensory and motor ar- ␮ ␮ m-wide, 25- m-deep vertical cortical eas but also association areas subserving ‘‘column’’ between the pia and the bot- the highest cognitive functions (8, 9, 11). tom of the cortex, because the ruler in The term cortical Although the anatomical and func- the graticule of the oil-immersion eye- ␮ tional columnarity of the neocortex has piece on their microscope had a 30- m ‘‘column’’ is used in so never been in doubt, the size, cell com- marker and their histological sections ␮ position, synaptic organization, expres- were 25 m thick; then, they estimated many ways that it can sion of signaling molecules, and function that the number of neurons within this of various types of ‘‘columns’’ are dra- ‘‘minicolumn’’ is 110 in all cytoarchitec- be very confusing to the matically different. Columns could be tonic areas examined, without any cor- nonspecialist. defined by cell constellation, pattern of rection for the cell size; and finally, connectivity, myelin content, staining based on this dubious finding, they property, magnitude of gene expression, made a broad generalization that the or functional properties. For example, magic number of 110 is constant in all studies are difficult to compare because there are ocular dominance columns, mammalian species (rodents, carnivore, Rockel et al. (1) counted the number of orientation columns, hypercolumns, and and primates, including human) in all neurons in very small vertical cylinders color columns, to mention only those cytoarchitectonic areas (except the pri- (minicolumns), whereas Herculano- described in the primary visual cortex mary visual cortex in primates). This Housel et al. estimated the density of (12), that differ from each other as well finding led them to conclude that, ‘‘the neurons in a larger volume of cortical intrinsic structure of the neocortex is tissue that can be more affected by the as from the columns of the alternating basically more uniform than has been amount of neuropile. However, the main callosal and ipsilateral projection in the thought and that differences in cytoar- goal of the work of Herculano-Housel et frontal lobe (8) or various minicolumns chitecture and function reflects differ- al. seems to be to dispel the lingering advocated by Szentgahotai (7), Eccles ences in connections.’’ perception that the data reported by (9), Buxhoeveden and Casanova (10), Most neuroscientists recognized the Rockel et al. are basically valid and to and a more recent detailed reconstruc- problems with both the method used emphasize, once again, that the simple tion of barrel field columns by Sakmann and the data obtained, but many found concept of basic uniformity of the cor- and colleagues (13) and their visibility in the simple concept of the uniformity of tex, which may appear attractive, is basi- vivo by neuroimaging (14). The only the cortex across various modalities as cally incorrect. I, however, feel that connections between these diverse struc- well as during evolution of neocortical Herculano-Housel et al. did not go far tures and concepts is that they refer to expansion highly attractive. Although at enough in addressing the related prob- the vertical or radial columnar organiza- least six research articles have directly lem that is caused by the frequent mis- tion of its elements as opposed to the refuted the accuracy of the data of use of the term ‘‘cortical column.’’ horizontal or laminar organization that Rockel et al. as well as the validity of Classical anatomists have emphasized is more explicit in histological prepara- their generalization (e.g., ref. 2), accord- the laminar deployment of the neocor- tions of the mature neocortex. Thus, the ing to the Institute of Scientific Infor- tex but were also aware of the promi- term cortical ‘‘column’’ is used in so mation (ISI), their article has been cited nent columnar organization as visualized Ϸ500 times. It is discussed often in the in Golgi impregnated material and as is major reference books of neuroscience particularly compelling in the Nissl- Author contributions: P.R. wrote the paper. and brain evolution, and is used widely stained sections of the human cerebral The author declares no conflict of interest. in computational models of cortical op- cortex (4). However, the concept of See companion article on page 12593. erations. The concept of uniformity functional columns received deserved *E-mail: [email protected].
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