A century of vision mapping in the human cerebral cortex
Ronald S. FISHMAN
By 1900, a consensus had arisen that the primary visual projection area was in the region of the calcarine cortex. E.A. Schaefer's textbook of physiology in 1900 was confident of this, but less confident of the exact representation of the visual field in this region. His "probable scheme" included an erroneous placement of central vision anteriorly and peripheral vision posteriorly, and made no mention of the magnification factor whereby the area devoted to central vision expands greatly in the projection from retina to cortex.
What was needed was a way of producing small discrete lesions in the human calcarine cortex and then studying the visual field defects that were produced. This was accomplished by World War I. The unprecedented use of artillery and the relatively exposed position of the head of soldiers huddling in the trenches made head wounds account for a quarter of all wounds. Instances where the wound was minor enough to allow survival and examination of the visual fields were reported by American, British, French and German authors. The most influential studies were that of Gordon Holmes, whose mapping of the visual field projection on the cortex was reproduced in textbooks virtually without change for 70 years.
In the 1990, the Holmes map was finally modified by Horton and Hoyt, who were able to apply modern brain imaging technique to the study of small calcarine lesions. This showed the magnification factor to be much greater than previously thought. They also make the case that the small quadrantic scotomas thought by Holmes to extend to the horizontal meridian represented wounds to V-2 in the peri-striate area outside of the calcarine cortex proper.
Application to the human of the laboratory finding of a multitiude of visual areas in the cat and monkey are still in an exploratory phase, but is leading to rethinking the vague and indefinite concept of "association" cortex.
Session VI -- 20th Century
Providence, Rhode Island, USA