Electrocorticographic mapping of human ventral visual areas

Abstract

Neuroimaging studies have enriched our knowledge about distinct functional modules in the human visual system, such as the fusiform face area or the parahippocampal place area. However, comprehensive functional architecture of the temporal cortex for object vision is unclear. To address this issue, we recorded electrocorticogram (ECoG) from a total of 394 electrodes, mainly located in the temporal cortex, in 4 human epileptic patients while they sequentially viewed 120 different visual stimuli. Each of the stimuli was a colore dphotograph of an object or a living creature from 24 different categories. ECoG signals from individual channels were analyzed in two ways. First,in order to evaluate visual responsiveness, we conducted fast fourier transformation and tested whether specific band powers increased during stimulation period compared to baseline period by paired t-test. Second, we conducted an analysis of variance to examine stimulus selectivity of peak-to-peak voltage of visually-evoked signals. We found that more than 85 percent of the channels located in the fusiform gyrus were responsive to at least one of the visual stimuli or exhibited selectivity to the visual objects such as faces, animals, foods, letter strings, and so on. The responsive channels were widely distributed along the antero-posterior axis in the fusiform gyrus and adjacent areas. The results indicated that visual objects are more continuously represented than previously thought in this region of the ventral temporal cortex.