Abstract
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.
Highlights
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]
Grand average waveforms of magnetic activity recorded in sensor-clusters over both hemispheres between 0–400 ms are displayed for men and women each in Fig. 1, showing a M100 peaking at 108 ms and 110 ms and the M170component with mean peak latencies of 169 ms and 165 ms
A two-way mixed ANOVA calculated for the M170-amplitude yielded a significant main effect for hemisphere (F 1,24 = 7.425; p = 0.01*) and significant interaction of gender x hemisphere (F 1,24 = 10.795; p = 0.003**) without significant effects of betweensubject comparison (p = 0.26)
Summary
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]. 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]. 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 FG contains the functionally defined so called fusiform face area (FFA) which is found to be engaged by face-stimuli [2]
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