Date Published: April 23, 2019
Publisher: Public Library of Science
Author(s): Lena Schwarz, Benjamin Kreifelts, Dirk Wildgruber, Michael Erb, Klaus Scheffler, Thomas Ethofer, John Richey.
Functional localizers are particularly prevalent in functional magnetic resonance imaging (fMRI) studies concerning face processing. In this study, we extend the knowledge on face localizers regarding four important aspects: First, activation differences in occipital and fusiform face areas (OFA/FFA) and amygdala are characterized by increased activation while precuneus and medial prefrontal cortex show decreased deactivation to faces versus control stimuli. The face-selective posterior superior temporal sulcus is a hybrid area exhibiting increased activation within its inferior and decreased deactivation within its superior part. Second, the employed control stimuli can impact on whether a region is classified in group analyses as face-selective or not. We specifically investigated this for recently described cytoarchitectonic subregions of the fusiform cortex (FG-2/FG-4). Averaged activity across voxels in FG-4 was stronger for faces than objects, houses, or landscapes. In FG-2, averaged activity was only significantly stronger in comparison with landscapes, but small peaks within this area were detected for comparison versus objects and houses. Third, reproducibility of individual peak activations is excellent for right FFA and quite good for right OFA, whereas within all other areas it was too low to provide valid information on time-invariant individual peaks. Finally, the fine-grained spatial activation patterns in right OFA and FFA are both time-invariant within each individual and sufficiently different between individuals to enable identification of individual participants with near-perfect precision (fMRI fingerprinting).
Faces constitute a privileged visual cue, enabling humans to recognize individuals from a virtually unlimited number of alternatives and extract a wealth of social (e.g. emotions, attitudes) and non-social (e.g. age, gender) information. The neural foundations of face perception consist of a distributed network of brain areas . The ‘core areas for face perception’ are the fusiform face area (FFA,  and the occipital face area (OFA, ), which are thought to extract invariant aspects of faces, and the posterior superior temporal sulcus (pSTS, ), processing changeable aspects of faces. The ‘extended network for face perception’  includes the amygdala subserving emotion processing  as well as the medial prefrontal cortex (mPFC), precuneus/posterior cingulate cortex (PC/pCC) and temporoparietal junction (TPJ) which are part of the default mode network (DMN, ), but process also information regarding familiarity  or mental states .
The current neuroimaging study allowed us to address several key questions of functional localizers. Specifically, we aimed to determine differential contributions of increased activation versus decreased deactivation within the face processing network. In addition, we explored to which extent definition of face-selectivity is dependent on the employed control condition. Finally, we investigated the stability of individual activation peaks in predefined ROIs of key areas for face perception and whether the activation patterns within these areas are characteristic and robust enough to identify individual participants with high precision.