Functional MRI Analysis of Body and Body Part Representations in the Extrastriate and Fusiform Body Areas

Abstract

This study examined the contributions of two previously identified brain regions—the extrastriate and fusiform body areas (EBA and FBA)—to the visual representation of the human form. Specifically we measured in these two areas the magnitude of fMRI response as a function of the amount of the human figure that is visible in the image, in the range from a single finger to the entire body. A second experiment determined the selectivity of these regions for body and body part stimuli relative to closely matched control images. We found a gradual increase in the selectivity of the EBA as a function of the amount of body shown. In contrast, the FBA shows a steplike function, with no significant selectivity for individual fingers or hands. In a third experiment we demonstrate that the response pattern seen in EBA does not extend to adjacent motion-selective human midtemporal area. We propose an interpretation of these results by analogy to nearby face-selective regions occipital face area (OFA) and fusiform face area (FFA). Specifically, we hypothesize that the EBA analyzes bodies at the level of parts (as has been proposed for faces in the OFA), whereas FBA (by analogy to FFA) may have a role in processing the configuration of body parts into wholes.