Four main theories concerning hemispheric asymmetries for emotional processing have been proposed: the right hemisphere hypothesis (RHH; the right hemisphere is specialized in processing all emotions), the valence hypothesis (VH; the left and the right hemispheres are superior in positive and negative emotion processing, respectively), the modified VH (the right-hemispheric superiority at posterior sites is followed by a valence-specific activity at frontal sites), and the motivational model (the left and the right hemispheres are superior in approaching-related and avoidance-related emotions, respectively). In a divided visual field paradigm, we presented happy and angry faces to 16 healthy participants, either unilaterally or bilaterally, in order to test the aforementioned theories. Behavioral results provided support for the VH and correlational analysis revealed that handedness influences the rightward bias for positive emotions. The amplitude of P1, N170, and P2 event-related potential components at parietal sites (selected by means of topographic maps) was larger in the right than in the left hemisphere, independently of the emotional expression of the stimuli, supporting the RHH. At frontal sites, no asymmetry was found in bilateral conditions, whereas in unilateral conditions, a mixed pattern of hemispheric asymmetries emerged. We conclude that there is no correspondence between behavioral and electrophysiological results concerning asymmetries for emotion processing, and that the VH and the RHH are not mutually exclusive. (PsycINFO Database Record

Microstate analysis applied to electroencephalographic signals (EEG) allows both temporal and spatial imaging exploration and represents the activity across the scalp. Despite its potential usefulness in understanding brain activity during a specific task, it has been mostly exploited at rest. We extracted EEG microstates during the presentation of emotional expressions, presented either unilaterally (a face in one visual hemifield) or bilaterally (two faces, one in each hemifield). Results revealed four specific microstate’s topographies: (i) M1 involves the temporal areas, mainly in the right hemisphere, with a higher occurrence for stimuli presented in the left than in the right visual field; (ii) M2 is localized in the left temporal cortex, with higher occurrence and coverage for unilateral than bilateral presentations; (iii) M3, with a bilateral temporo-parietal localization, shows higher coverage for bilateral than unilateral presentation; (iv) M4, mainly localized in the right fronto-parietal areas and possibly representing the hemispheric specialization for the peculiar stimulus category, shows higher occurrence and coverage for unilateral stimuli presented in the left than in the right visual field. These results suggest that microstate analysis is a valid tool to explore the cerebral response to emotions and can add new insights on the cerebral functioning, with respect to other EEG markers.