Localization of extrastriate body area using functional near-infrared spectroscopy and 3D digitizer

The extrastriate body area (EBA) is a brain region that responds selectively to visual stimuli of human bodies or body parts. Previous studies using functional magnetic resonance imaging (fMRI) have shown that EBA occupies a relatively small region and varied across subjects in its anatomical location. This study investigated whether EBA activity can be detected by functional near-infrared spectroscopy (fNIRS) that imposes few physical constraints on the subjects and has higher temporal but lower spatial resolutions compared to fMRI. For this purpose the subject´s brain activity in the occipitotemporal area during observation of images of body parts and objects was measured using fNIRS. The NIRS optode positions were recorded using a 3D digitizer and mapped onto a probabilistic anatomical model. We found that the activity in the occipitotemporal region during observation of body stimuli was significantly greater than that of object stimuli in 11 out of 16 subjects. The group analyses also showed that channels located near the position where the previous studies reported EBA activation were more activated during observation of the body stimuli compared to the object stimuli. The spatial variance of those channels among subjects was relatively small. These results suggest that EBA activity and its anatomical location can be sufficiently measured by using fNIRS and a 3D digitizer.