It is well established that the human brain is composed of two hemispheres specialized in the processing of specific information: left hemisphere is specialized in the processing of verbal information, while right hemisphere is specialized in the processing of visuospatial information. This divided work between the hemispheres is called “hemispheric lateralization”. However, hemispheres closely communicate and exchange information through the corpus callusum. Many studies have investigated the time and latency of transfer of information intra- and inter-hemispheres using ERPs (event-related potentials) technique.
This study aim at investigating sex differences in the lateralization and in the inter-hemispheric transmission times (IHTTs) at the level of the first visual ERP components (P1 and N170) during face identity encoding and EEG registration. This task relies mostly on global processing implemented in the right hemisphere, especially at the level of the early N170 ERP component.
12 women and 12 men (age range: 21 to 32 years) performed an identity-matching task: they were asked to decide if a probe face (briefly presented either in the left or in the right visual field) belonged to the same person or not.
The Authors did not find lateralization-related and sex-related differences in the P1 characteristics, while these two factors modulated the N170. N170 amplitudes, latencies and the derived IHTTs suggested a clear asymmetry in men, in terms of a right hemisphere dominance (i.e. shorter “left-to-right” transfer than “right-to-left” transfer). Women showed a more divided work between the hemispheres (a more bilateral functioning), with a tendency toward a left hemisphere advantage.
Possible explanations may be that (i) in women the left hemisphere is the one specialized for face-encoding; (ii) women use more local information than men when they must encode identity; (iii) women perform the task with an added semantic or verbal strategy requiring the left hemisphere during face processing as compared to a “pure” perceptual-based analysis in men.
These results generalize previous findings and indicate longer transfers from the specialized to the non-specialized hemisphere (i.e. from right to left than viceversa), especially in the male brain. Because asymmetries started from the N170 component, the first electrophysiological index of high-level perceptual processing on face representations, they also suggest a functional account for hemispheric lateralization and sex-related differences rather than a structural one.