Contrasting Hemispheric Asymmetries for Emotional Processing From Event-Related Potentials and Behavioral Responses

Objective: 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). Method: 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. Results: 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. Conclusions: 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. General Scientific Summary We investigated cerebral asymmetry for positive and negative emotions (happiness and anger), starting from the central role of emotions in everyday life. The results revealed that negative emotions are mainly processed in the right hemisphere. Concerning positive emotions, electrophysiological results confirmed right-hemispheric superiority, whereas our behavioral findings showed left-hemispheric superiority, which was stronger in participants with a stronger right-hand preference. We conclude that hand preference can influence the hemispheric asymmetries for positive emotions.