A stimulating view of human visual cortex

Mapping of the visual cortex is a difficult process, but great steps have been taken. The advances result from 1) careful study of individual patients and 2) new technologies such as functional MRI and PET. In this issue, Lee et al. demonstrate that neurons in discrete areas of the human cortex are functionally organized to detect color, shape, and motion1 in patterns comparable to those of nonhuman primates.2 They used subdural grid electrodes in 23 epilepsy patients to stimulate distinct areas of visual cortex, even including the basal occipital lobes. Stimulation of striate cortex elicited simple form responses such as blobs of light, whereas complex forms were produced by stimulation of the basal and lateral temporo-occipital cortex. Lee et al. also confirm that the fusiform and lingual gyri are important in color processing and that motion detection is concentrated at the temporal-parieto-occipital junctions and the basal temporal-occipital cortex.

Near the end of the 19th century, Henschen correctly localized the primary visual cortex to the calcarine fissure.3 He also recognized that hemianopic defects were the result of striate cortex injury and that specific areas of the visual field projected to …