Brain Mechanisms of Vision Author(s): David H. Hubel and Torsten N. Wiesel Source: Scientific American , Vol. 241, No. 3 (September 1979), pp. 150-163 Published by: Scientific American, a division of Nature America, Inc. Stable URL: https://www.jstor.org/stable/10.2307/24965293 JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at https://about.jstor.org/terms Scientific American, a division of Nature America, Inc. is collaborating with JSTOR to digitize, preserve and extend access to Scientific American This content downloaded from 128.61.154.29 on Mon, 06 Jan 2020 20:23:07 UTC All use subject to https://about.jstor.org/terms of Brain Mechanisms Vision A functional architecture that may underlie processing of sensory information in the cortex is revealed by studies of the activity and the organization in space of neurons in the primary visual cortex by David H. Hubel and Torsten N. Wiesel iewed as a kind of invention by feet. (In a 1963 article in Scientific Amer­ of the location (at the surface of the evolution, the cerebral cortex ican one of us gave the area as 20 square brain) of the electrical brain waves pro­ must be one of the great success feet and was quickly corrected by a neu­ duced when an animal was stimulated storiesV in the history of living things. In roanatomist friend in Toronto, who said by touching the body, sounding clicks vertebrates lower than mammals the ce­ he thought it was 1.5 square feet-"at or tones in the ear or flashing light in rebral cortex is minuscule, if it can be least that is what Canadians have.") The the eye. Similarly, motor areas could said to exist at all. Suddenly impressive folding is presumably mainly the result be mapped by stimulating the cortex in the lowest mammals, it begins to of such an unlikely structure's having to electrically and noting what part of the dominate the brain in carnivores, and it be packed into a box the size of the skull. animal's body moved. increases explosively in primates; in A casual glance at cortical tissue un­ man it almost completely envelops the der a microscope shows vast numbers of his systematic mapping of the cortex rest of the brain, tending to obscure the neurons: about 1 05 (100,000) for each Tsoon led to a fundamental realiza­ other parts. The degree to which an an­ square millimeter of surface, suggesting tion: most of the sensory and motor imal depends on an organ is an index that the cortex as a whole has some 10lD areas contained systematic two-dimen­ of the organ's importance that is even (10 billion) neurons. The cell bodies are sional maps of the world they represent­ more convincing than size, and depen­ arranged in half a dozen layers that are ed. Destroying a particular small region dence on the cortex has increased rapid­ alternately cell-sparse and cell-rich. In of cortex could lead to paralysis of one ly as mammals have evolved. A mouse contrast to these marked changes in cell arm; a similar lesion in another small without a cortex appears fairly nor­ density in successive layers at different region led to numbness of one hand or mal, at least to casual inspection; a man depths in the cortex there is marked uni­ of the upper lip, or blindness in one without a cortex is almost a vegetable, formity from place to place in the plane small part of the visual world; if elec­ speechless, sightless, senseless. of any given layer and in any direction trodes were placed on an animal's cor­ Understanding of this large and indis­ within that plane. The cortex is morpho­ tex, touching one limb produced a cor­ pensable organ is still woefully defi­ logically rather uniform in two of its respondingly localized series of electric cient. This is partly because it is very dimensions. potentials. Clearly the body was system­ complex, not only structurally but also One of the first great insights about atically mapped onto the somatic senso­ in its functions, and partly because neu­ cortical organization came late in the ry and motor areas; the visual world robiologists' intuitions about the func­ 19th century, when it was gradually re­ was mapped onto the primary visual tions have so often been wrong. The out­ alized that this rather uniform plate of cortex, an area on the occipital lobe that look is changing, however, as techniques tissue' is subdivided into a number of in man and in the macaque monkey (the improve and as investigators learn how different regions that have very differ­ animal in which our investigations have to deal with the huge numbers of intri­ ent functions. The evidence came from mainly been cond ucted) covers about 15 cately connected neurons that are the clinical, physiological and anatomical square centimeters. basic elements of the cortex, with the sources. It was noted that a brain injury, In the primary visual cortex the map impulses they carry and with the syn­ depending on its location, could cause is uncomplicated by breaks and discon­ apses that connect them. In this article paralysis or blindness or numbness or tinuities except for the remarkable split we hope to sketch the present state of speech loss; the blindness could be total of the visual world down the exact mid­ knowledge of one subdivision of the or limited to half or less of the visual dle, with the left half projected to the cortex: the primary visual cortex (also world, and the numbness could involve right cerebral cortex and the right half known as the striate cortex or area 17), one limb or a few fingers. The consisten­ projected to the left cortex. The map of the most elementary of the cortical re­ cy of the relation between a given defect the body is more complicated and is still gions concerned with vision. That will and the location of the lesion gradually perhaps not completely understood. It is necessarily lead us into the related sub­ led to a charting of the most obvious nonetheless systematic, and it is similar­ ject of visual perception, since the work­ of these specialized regions, the visual, ly crossed, with the right side of the ings of an organ cannot easily be sepa­ auditory, somatic sensory (body sensa­ body projecting to the left hemisphere rated from its biological purpose. tion), speech and motor regions. and the left side projecting to the right In many cases a close look with a mi­ hemisphere. (It is worth remarking that he cerebral cortex, a highly folded croscope at cortex stained for cell bod­ no one has the remotest idea why there Tplate of neural tissue about two mil­ ies showed that in spite of the relative should be this amazing tendency for ner­ limeters thick, is an outermost crust uniformity there were structural varia­ vous-system pathways to cross.) wrapped over the top of, and to some tions, particularly in the layering pat­ An important feature of cortical maps extent tucked under, the cerebral hemi­ tern, that correlated well with the clin­ is their distortion. The scale of the maps spheres. In man its total area, if it were ically defined subdivisions. Additional varies as it does in a Mercator projec­ spread out, would be about 1.5 square confirmation came from observations tion, the rule for the cortex. being that 150 © 1979 SCIENTIFIC AMERICAN, INC This content downloaded from 128.61.154.29 on Mon, 06 Jan 2020 20:23:07 UTC All use subject to https://about.jstor.org/terms OCULAR-DOMINANCE COLUMNS, one of the two major sys­ ence. The autoradiograph was made by injecting a radioactively la­ tems that characterize the functional architecture of the primary vi­ beled amino acid into the right eye of an anesthetized animal. The sual cortex, are revealed as periodic hright patches in this dark-field amino acid was taken up by cell bodies in the retina and transport­ autoradiograph of a section of macaque monkey cortex. The columns ed via the lateral geniculate nucleus, a way station in the brain, to (actuaUy curving slabs of cortex, seen here in cross section in a brain cells in the cortex. A brain slice was coated with a photographic emul­ slice cut perpendicularly to the surface) are regions in which all neu­ sion, which was exposed for several months and then developed. Ex­ rons respond more actively to the right eye than to the left one; dark posed silver grains overlying the regions of radioactivity form the regions separating the bright patches are columns of left-eye prefer- light-scattering patches that represent ocular-dominance columns. DOMINANCE PATTERN is seen face on in an axonal-transport the label therefore accumulates. This section was cut in a plane tan­ autoradiograph of a brain section parallel, rather than perpendicu­ gential to the dome-shaped surface of the cortex and just below lay­ lar, to the surface of the primary visual cortex. As can be seen in the er IV, which therefore appears as a ring of roughly parallel bright autoradiograph at the top of the page, the label is brightest in one bands. These are the radioactively labeled ocular-dominance regions, layer of the folded cortex, layer IV.