Mapping of functional organization in human visual cortex - Electrical cortical stimulation

Objectives: To investigate the pattern of functional organization in the hu man visual cortex through electrical cortical stimulation. Methods: Electri cal cortical stimulation was applied to the occipital cortex and adjacent c ortices using subdural grid electrodes in 23 epilepsy patients. Diverse vis ual responses were recorded. These responses were divided into different ca tegories according to the specific response modalities, such as form, color , and motion. Form visual responses were further subdivided into simple, in termediate, and complex responses. The cortical localization of subdural el ectrodes was identified using MRI-CT coregistration, The cortical distribut ion of different visual responses was projected into three-dimensional surf ace renderings of the brain. The distribution and frequency of subdural ele ctrodes showing different visual responses were quantified by calculating t he percentage of the number of electrodes showing one specific type of visu al response at the corresponding anatomic region to the total number of ele ctrodes in all brain regions that produced the same response. Results: Simp le form responses mere obtained mostly at the occipital pole and the inferi or occipital gyrus (47.4%) and the striate cortex (42.4%). Intermediate for m responses occurred mainly on the peristriate cortex (52.5%) and the later al occipital (28.0%) and fusiform gyri (19.5%). Complex forms were produced by stimulation of the basal temporo-occipital region (57.6%) and the later al temporal or lateral temporo-occipital junctional region (42.4%), Color r esponses occurred on the basal occipital area, mostly at the fusiform (40.0 %) and lingual gyri (36.0%). Moving sensations were evoked by stimulation o f the basal temporo-occipital (28.4%) and the mesial parietooccipital or te mporo-parieto-occipital junctional regions (23.9%). Conclusions: Different modalities of vision, such as form, color, and moving sensation, appeared t o be distributed and organized in different areas of the human visual corte x.