Sex-Differences of Face Coding: Evidence from Larger Right Hemispheric M170 in Men and Dipole Source Modelling

Lueschow A (2013) Sex-Differences of Face Coding: Evidence from Larger Right Hemispheric M170 in Men and Dipole Source Modelling. PLoS ONE 8(7): e69107. doi:10.1371/journal.pone.0069107 Sex-Differences of Face Coding: Evidence from Larger Right Hemispheric M170 in Men and Dipole Source Modelling Hannes O. Tiedt 0 Joachim E. Weber 0 Alfred Pauls 0 Klaus M. Beier 0 Andreas Lueschow 0 Jason Jeremy Sinclair Barton, University of British Columbia, Canada 0 1 Department of Neurology, Charite - Universita tsmedizin Berlin, Campus Benjamin Franklin , Berlin, Germany , 2 Institute of Sexology and Sexual Medicine, Charite - Universita tsmedizin Berlin , Berlin , Germany The processing of faces relies on a specialized neural system comprising bilateral cortical structures with a dominance of the right hemisphere. However, due to inconsistencies of earlier findings as well as more recent results such functional lateralization has become a topic of discussion. In particular, studies employing behavioural tasks and electrophysiological methods indicate a dominance of the right hemisphere during face perception only in men whereas women exhibit symmetric and bilateral face processing. The aim of this study was to further investigate such sex differences in hemispheric processing of personally familiar and opposite-sex faces using whole-head magnetoencephalography (MEG). We found a right-lateralized M170-component in occipito-temporal sensor clusters in men as opposed to a bilateral response in women. Furthermore, the same pattern was obtained in performing dipole localization and determining dipole strength in the M170-timewindow. These results suggest asymmetric involvement of face-responsive neural structures in men and allow to ascribe this asymmetry to the fusiform gyrus. This specifies findings from previous investigations employing event-related potentials (ERP) and LORETA reconstruction methods yielding rather extended bilateral activations showing left asymmetry in women and right lateralization in men. We discuss our finding of an asymmetric fusiform activation pattern in men in terms of holistic face processing during face evaluation and sex differences with regard to visual strategies in general and interest for opposite faces in special. Taken together the pattern of hemispheric specialization observed here yields new insights into sex differences in face perception and entails further questions about interactions between biological sex, psychological gender and influences that might be stimulus-driven or task dependent. - The highly specialized skill of face perception in humans is a function of a bilaterally organized neural system [1] with a supposed dominance of the right hemisphere [2] which emerges during development of cognitive functions [3]. The processing of faces involves occipito-temporal regions and most notably the fusiform gyrus (FG) which is consistently found to respond specifically to faces (for a review and argumentation in favour of domain-specific mechanisms underlying face-recognition see [4]) and may function as an entry node to subsequent processing in a more widespread cortical network [5,6]. However, recent investigations indicate that hemispheric asymmetries in face processing may at least be partially due to a higher degree of functional lateralisation in men compared to women [7]. Analogous findings have been obtained for visuospatial abilities, e.g. mental rotation [8] and language functions [9]. In particular, studies on face processing employing behavioural tasks such as chimeric face perception or presentation of faces selectively to the right or left visual field demonstrate a higher degree of functional lateralisation to the right hemisphere in men with a more bilateral ability in women [10,11]. ERP-studies found an increased amplitude of the face-specific N170-component in the right hemisphere only in male subjects with no such laterality effects in women [7]. The N170-response reflects structural encoding of faces [12] and in most instances correlates with the N200-component in intracranial recordings [13] and the M170-component in MEG-recordings [14,15]. Although sometimes seen as the otherwise equivalent magnetic counterpart of the N170-component there are a few marked differences concerning the M170 due to differential sensitivity to source orientation of EEG and MEG [16,17]. Thus, the M170 has been found to originate primarily from sources within the FG [15,18] whereas the N170 is to a larger extent influenced by sources in other face-responsive regions, e.g. in the superior temporal sulcus (STS) [19]. The FG contains the functionally defined so called fusiform face area (FFA) which is found to be specifically engaged by face-stimuli [2]. Here, we used whole-head-MEG to study whether sexdifferences in face processing are reflected in early face-specific event-related magnetic fields (ERFs), i.e. the M100 [14] and M170 [15]. Materials and Methods Subjects Twenty-six adult subjects (13 females; mean age = 25.46 years, Range 2035) who were right-handed by self-report participated in the study. All participants had normal or corrected to normal vision and none had a history of neurological, psychiatric or any other relevant disorders. They did not have metallic implants or any other ferromagnetic objects on them. All participants gave their informed written consent prior to the experiment. The study was approved by the Local Ethics Committee (Ethikausschuss Campus Benjamin Franklin, Charite Universitatsmedizin, Berlin). Stimuli and Procedure The participants provided digital photographs displaying opposite-sex faces of personally familiar persons (partner and close friends). Out of the provided photographs 3 pictures of each category (partner, 2 friends) were singled out and processed to fit the requirements of the experiments; the faces of the persons were cut out and only pictures displaying frontal views of faces lacking possibly distracting features such as unique hairdressing, glasses etc. were selected. All faces had either neutral or positive expressions without differences between face-categories or gender. The pictures were arranged to a size of 1006100 pixels and projected on a screen in front of the subjects with a viewing angle of 11.5u. The MEG-measurements were conducted in a magnetically shielded room using a whole-head (Eagle TechnologyTM, ET160) employing 93 first order gradiometers with a baseline of 5 cm. The experimental procedure consisted of a passive viewing paradigm; all subjects were instructed to avoid head and eye movements and to view the pictures and simultaneously imagine a comfortable situation. All faces were presented 30 times each in a randomized order with variable interstimulus intervals and for 6000 ms. The purpose of including emotional imagery and using lengthier presentation times was to study late and sustained shifts of magnetic activity related to the late positive potential (LPP (...truncated)