Remote Effects of OFA Disruption on the Face Perception Network Revealed by Consecutive TMS-FMRI

The face perception system is comprised of a network of connected regions including the middle fusiform gyrus (“fusiform face area” or FFA), the inferior occipital gyrus (“occipital face area” or OFA), and the posterior part of the superior temporal sulcus. These regions are typically active bilaterally but may show right hemisphere dominance. The functional magnetic resonance imaging (fMRI) response of the right FFA is normally attenuated for face stimuli of the same compared to different identities, called fMR-adaptation. The recovery in fMRI signal, or release from fMR-adaptation, for faces of different identities indicates that the neural population comprising the FFA is involved in coding face identity. Patients with prosopagnosia who are unable to visually recognize faces and who show right OFA damage, nonetheless show face-selective activation in the right FFA (Rossion et al., 2003; Steeves et al., 2006). However, the sensitivity to face identity is abnormal in the right FFA and does not show the typical release from adaptation for different face identities (Steeves et al., 2009). This indicates that in these patients the FFA is not differentiating face identity and suggests that an intact right OFA is integral for face identity coding. We used offline repetitive transcranial magnetic stimulation (TMS) to temporarily disrupt processing in the right OFA in healthy subjects. We then immediately performed fMRI to measure changes in blood oxygenation level dependent (BOLD) signal across the face network using a face fMR-adaptation paradigm. We hypothesized that TMS to the right OFA would induce abnormal face identity coding in the right FFA, reflected by a decreased adaptation response. Indeed, activation for different but not same identity faces in the right FFA decreased after TMS was applied to the right OFA compared to sham TMS and TMS to a control site, the nearby object-selective right lateral occipital area (LO). Our findings indicate that TMS to the OFA selectively disrupts face but not butterfly identity coding in both the OFA and FFA. Congruent with mounting evidence from both patients and healthy subjects, here we causally demonstrate the importance of the often-overlooked OFA for normal face identity coding in the FFA.