Ablation of Visual Areas in the Central Nervous System

It is now apparent that visual pattern discrimination in the cat and possibly in the tree shrew or rat, can survive loss of the striate cortex, and raises difficult questions concerning the functions and organization of the neocortical visual system.

Abstract

Experiments utilizing ablation of cerebral tissue fall into two classes, those which leave a particular behavior undisturbed and thus demonstrate that the tissue removed is nonessential to the behavior; and those which disrupt the behavior under study. Results in the former case may be trivial, as they frequently were prior to adequate knowledge of the functional anatomy of the cerebral cortex. For instance, Franz (1911) performed a careful study of vision following occipital lobectomy in monkeys, but came to erroneous conclusions by missing what is now known to be the representation of the fovea in the far lateral striate cortex (and probably also the deeply concealed anterior tip of the striate area). Presently available techniques should preclude repetition of this type of error. The functional state of surviving tissue can be assayed electrophysiologically and the extent and location of a neocortical lesion can be checked against retrograde thalamic degeneration1. Using such criteria it is now apparent that visual pattern discrimination (Fig. 4) in the cat (Doty, 1961b, 1971; Spear and Braun, 1969; Wetzel et al., 1965; Winans, 1967) and possibly in the tree shrew (Snyder and Diamond, 1968) or rat (Lewellyn et al., 1969), can survive loss of the striate cortex. In view of the elaborate physiological processing of visual information known to occur in the striate cortex (e.g., Hubel and Wiesel, 1962) this result is clearly unexpected and raises difficult questions concerning the functions and organization of the neocortical visual system.