Trends in Cognitive Sciences
ForumThe improbable simplicity of the fusiform face area
Introduction
Nearly a decade ago, Semir Zeki discussed improbable visual areas in the primate brain [1] (see also [2]). In his critique, Zeki questioned the accuracy and theoretical logic of defining extrastriate cortical areas based on partial retinotopic maps as well as the variable parcellation criteria used across research groups. However, his discussion stopped at human V4 and did not extend into VTC where high-level visual representations for faces, body parts, objects, and places are located (Figure 1a). We apply Zeki's concerns of accuracy and parcellation criteria to the FFA and ask: Does the FFA exist in the way it is depicted in journals, textbooks, and everyday media – as a ‘blueberry-sized’ module on the fusiform gyrus [3]? To address this question, we first discuss various depictions of the FFA and highlight factors contributing to this variability. We then summarize a recent organizational framework developed to reconcile the many faces of the FFA and to accommodate complexities of VTC organization more generally.
Section snippets
Functional localizer approach identifies the FFA but is it time for an update?
The classic work by Kanwisher and colleagues has been highly influential – ushering in nearly 2500 citations in the past 15 years – for introducing the elegant functional localizer method to the field of functional magnetic resonance imaging (fMRI) and for convincingly demonstrating the existence of face-selective regions in the human brain [4]. The localizer approach first identifies a region of interest in individual subjects with one set of data (e.g. comparing fMRI responses to images of
FFA: multiple and discontinuous, smoothed and simplified, or hindered by artifacts
The complexity begins when experimenters run an FFA localizer only to find approximately eight face-selective clusters across ventral and lateral aspects of the temporal lobe depending on the scanning parameters used 4, 6, 7, 10 (VTC shown in Figure 1b–d). Often, more than one face-selective region is detected on the fusiform gyrus (Figure 1b–d) 4, 6, 7, 8, 9, 10, 11. Aligning with the influential theoretical model, researchers commonly combine all fusiform face-selective regions into the FFA (
Solution: anatomy matters
Improved scanning methods enable consistent localization of several face-selective regions in VTC when considering their spatial organization relative to surrounding regions and neuroanatomical landmarks 8, 9 (Figure 2a). Such an approach reveals that face-selective regions are discontinuous and organized within and across subjects as opposed to discontinuous and variable as commonly reported. Specifically, face-selective regions have a periodic nature where each region is approximately 10 mm in
Concluding remarks
It is not improbable that neural responses specific to faces cluster in the human brain. However, it is unlikely that face-selective responses cluster in a fashion consistent with the present description of the FFA. Instead, methodological factors such as spatial smoothing and fMRI artifacts contribute to the complexity and changing presence of face-selective responses. Zeki [1] concluded his paper with the notion that traditional and even conservative criteria have considerable merit when
Acknowledgments
This work was supported by NSF BCS grant 0920865 and Round 4 Bio-X IIP award. We thank Melina Uncapher, Nick Davidenko, Alina Liberman, and three anonymous reviewers for helpful comments on prior versions of this manuscript.
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2022, NeuropsychologiaCitation Excerpt :In all these studies, connections are less dense – or reduced in connection strength/connectivity probability - between EVC and the FFA than between EVC and the spatially closer OFA (Gschwind et al., 2012; Wang et al., 2020). This appears to be the case also in the most recent study of Finzi et al.(2021), in which the FFA complex is divided in two clusters (pFus and mFus, after Weiner and Grill-Spector, 2010; or pFus-faces and mFus-faces; after Weiner and Grill-Spector, 2012, Fig.10) and the EVC holds direct connections with each of these clusters (in all participants in which these regions are successfully localized (Fig.6 in Finzi et al., 2021; see Fig.11&B here). Thus, despite the longer spatial distance between EVC and FFA than EVC and OFA, and the dominance of short-range fibers in the cortical face network overall (Wang et al., 2020), DTI studies considered together overwhelmingly support the early hypothesis of direct connections from EVC to the FFA complex (Rossion et al., 2003; Rossion, 2008, Figs.6 and 7), against a strict hierarchical view of the cortical face network.