EBA-related body-preferring responses in the occipitotemporal cortex measured with functional near-infrared spectroscopy.

Background: The extrastriate body area (EBA) is involved in the visual processing of bodies and body parts, but most evidence for its response profile comes from fMRI. We examined whether fNIRS can detect body-preferring occipitotemporal responses consistent with EBA-related processing. Methods: Sixty university students passively viewed non-hand body parts, hands, and objects. HbO responses were estimated using a block-level general linear model, with the three conditions matched in temporal structure. For each participant, a leave-one-subject-out (LOSO) procedure used the other 59 participants to select left and right functional peak channels within anatomically guided EBA-related occipitotemporal channel pools. This reduced direct participant-level circularity but did not provide dataset-level independence or independently localized EBA ROIs. Preprocessing included linear detrending, temporal derivative distribution repair, and 0.01-0.08-Hz band-pass filtering. An additional ICA preprocessing step with a conservative noise identification threshold was applied to attenuate spatially widespread noise components. Results: In the primary analysis, both the body-object and body-hand contrasts were significant for the left and right LOSO-selected functional peak channels and the bilateral average after FDR correction. Following additional ICA preprocessing, both contrasts remained significant for the left functional peak channel and the bilateral average, but not for the right functional peak channel. Conclusion: Non-hand body parts elicited stronger HbO responses than objects and hands in posterior temporal-occipital cortex. The left-hemisphere and bilateral effects were significant in both analyses, whereas the right-sided effects were significant only in the primary analysis. Although the absence of short-separation measurements precluded complete separation of cortical and extracerebral contributions, the findings support the feasibility of measuring body-preferring occipitotemporal responses consistent with EBA-related processing using fNIRS; they do not establish direct anatomical localization of the EBA.