The Trajectory of Hemispheric Lateralization in the Core System of Face Processing: A Cross-Sectional Functional Magnetic Resonance Imaging Pilot Study

Abstract

Face processing is mediated by a distributed neural network commonly divided into a “core system” and an “extended system.” The core system consists of several, typically right-lateralized brain regions in the occipito-temporal cortex, including the occipital face area (OFA), the fusiform face area (FFA) and the posterior superior temporal sulcus (pSTS). It was recently proposed that the face processing network is initially bilateral and becomes right-specialized in the course of the development of reading abilities due to the competition between language-related regions in the left occipito-temporal cortex (e.g., the visual word form area, VWFA) and the FFA for common neural resources. In the present pilot study, we assessed the neural face processing network in 12 children (aged 7–9 years) and 10 adults with functional magnetic resonance imaging (fMRI). The hemispheric lateralization of the core face regions was compared between both groups. The study had two goals: First, we aimed to establish an fMRI paradigm suitable for assessing activation in the core system of face processing in young children at the single subject level. Second, we planned to collect data for a power analysis to calculate the necessary group size for a large-scale cross-sectional imaging study assessing the ontogenetic development of the lateralization of the face processing network, with focus on the FFA. It was possible to detect brain activity in the core system of 75% of children at the single subject level. The average scan-to-scan motion of the included children was comparable to adults, ruling out that potential activation differences between groups are caused by unequal motion artifacts. Hemispheric lateralization of the FFA was 0.07 ± 0.48 in children (indicating bilateral activation) and −0.32 ± 0.52 in adults (indicating right-hemispheric dominance). These results thus showed, as expected, a trend for increased lateralization in adults. The estimated effect size for the FFA lateralization difference was d = 0.78 (indicating medium to large effects). An adequately powered follow-up study (sensitivity 0.8) testing developmental changes of FFA lateralization would therefore require the inclusion of 18 children and 26 adults.

With Childhood Hemispherectomy, One Hemisphere Can Support--But is Suboptimal for--Word and Face Recognition

“…On the other hand, these hemispheric superiorities appear to emerge over development and are not fully mature in children (Dehaene et al, 2010; Scherf et al, 2007). In childhood, it is conjectured that faces are initially represented bilaterally (Hildesheim et al, 2020). Only over time, as a result of the pressure associated with literacy acquisition, does word representation come to compete for representation in the LH (Dehaene-Lambertz et al, 2018; Dundas et al, 2014; Nordt et al, 2020).…”

Comparison of Scalp ERP to Faces in Macaques and Humans

“…There are many studies of face responses in both humans and macaques. Human studies show consistent bias that cortical face response is larger on the right side (Rossion et al, 2003;Hildesheim et al, 2020). Such bias has not been addressed in macaques.…”

Hemispheric Asymmetry in Visual Processing: An ERP Study on Spatial Frequency Gratings

“…From a broader perspective, this line of evidence might also account for the left hemispheric lateralization of the visual word form area (VWFA, namely the fusiform gyrus of the occipito/temporal cortex) devoted to orthographic processing [49,50], since letters are characterized by higher spatial frequencies. On the opposite side, the right hemispheric advantage for low spatial frequencies, global processing would explain the right-sided lateralization (at least in the male brain) of the fusiform face area (FFA) for the holistic recognition of faces [51,52].…”