Localization in the Visual Cortex

Abstract

DR. GORDON HOLMES, in his Ferrier Lecture before the Royal Society on "The Organisation of the Visual Cortex in Man" (Proc. Roy. Soc., B, 132, 348; 1945), dealt chiefly with the question of localization within the visual area of the cerebral cortex. As he himself has shown, by study of the visual-field defects resulting from gunshot wounds of the cortex, there is apparently a very sharp point-to-point representation of the retina in the cortex. The conception of definite fixed anatomical connexions between each point of the retina and the corresponding point in the cortex has been supported by recent histological studies of the actual nerve fibre connexions, particularly by Le Gros Clark. Such a rigid fixed relationship between retina and cortex would appear, however, to stand in marked contrast to the situation in other parts of the cortex, notably the motor area, where localization is by no means sharp and undergoes considerable physiological variations. But more recent clinical studies have shown that there must be a good deal of plasticity in the functional organization of the visual cortex. For example, patients suffering from hemianopia compensate for the loss of half the visual field by developing a new fixation point ('false macula') in the centre of the surviving field of vision; a similar adaptation occurs in a squinting eye. In such cases there must be a complete functional reorganization in the cortex, though the fibre connexions, of course, cannot change. The conclusion is that, although there is an accurate point-to-point representation of the retina in the cortex, the functional organization of the visual cortex is not thereby rigidly fixed; on the contrary, it exhibits considerable plasticity.