ON THE ROLE OF TERTIARY SULCI IN DEVELOPMENTAL PROSOPAGNOSIA

Abstract

Ventral temporal cortex (VTC) is critical for high‐level visual processing such as face and object recognition (Grill‐Spector & Weiner, 2014). Anatomically, VTC is bounded by the occipitotemporal (OTS) and collateral (CoS) sulci, and is also divided into lateral and medial partitions by the mid‐fusiform sulcus (MFS). The MFS is a critical microarchitectonic and functional landmark, in that the MFS identifies (i) cytoarchitectonic transitions among four distinct areas in the fusiform gyrus, (ii) transitions in large‐scale functional maps and (iii) the location of fine‐scale functional regions (Weiner, 2019). Morphologically, the shallowness of the MFS is very stable, while its length is much more variable, ranging from just under 3 millimeters to over 5 centimeters. Nevertheless, it is presently unknown if individual differences in MFS length predict individual differences in perception. To fill this gap in knowledge, we leveraged two previously published datasets of T1‐weighted magnetic resonance images (MRI) for 82 subjects consisting of 39 developmental prosopagnosics (DPs) and 43 typical controls (Dataset 1: 17 DPs (11 females, mean age: 30.9 y) and 18 controls (11 females, mean age: 28.9 y); Dataset 2: 22 DPs (15 females, mean age: 41.9 y) and 25 typical adults (15 females, mean age: 42.3 y; Garrido et al., 2009; Jiahui et al., 2018)). DPs are 2—2.5% of the population who have severe deficits recognizing the faces of familiar people without accompanying insult to the brain (Garrido et al., 2008, 2009; Jiahui et al., 2018; Duchaine and Yovel, 2015; Duchaine and Nakayama, 2005; Corrow et al., 2016). This condition runs in families suggesting a genetic origin. Each participant also participated in a behavioral face recognition test, the Cambridge Face Memory Test (CFMT). We implemented a fourfold analysis approach. First, we reconstructed the cortical surface for all subjects using FreeSurfer. Second, we manually defined the MFS, OTS, and CoS in each hemisphere. Third, for each of three sulci, we compared sulcal length and depth across groups. Fourth, we calculated the correlation between any metric that was different between groups and CFMT score. This approach revealed three main findings. First, the MFS was characteristically shallower in DPs and controls compared to the OTS and CoS (F(2, 480), p<.001) with no difference in depth between groups (F(1, 480), p=.97). Second, the MFS was consistently shorter in DPs compared to controls (F(1, 159), p<.03). Third, MFS length in the right hemisphere predicted CFMT score in controls (r=.34, p<.03), but not DPs (r=−.14, p=.38) in which a longer MFS predicted a higher CFMT score. In conclusion, our results document morphological differences in tertiary sulcal folding between DPs and controls. Since tertiary sulci in VTC emerge around 40–44 weeks in humans (Chi et al., 1977), this provides a developmental origin regarding when these morphological differences between DPs and controls may begin.Support or Funding InformationFunding for this research was provided by:Dartmouth’s Rockefeller Center Economic and Social Research Council (RES‐061‐23‐0400 to B.D.)