Brain asymmetry in emotional processing in Asperger syndrome

The role of brain asymmetry in emotional processing in Asperger syndrome (AS) is still largely unknown. Although the valence hypothesis predicts that positive emotions are processed preferentially by the left hemisphere and negative emotions by the right hemisphere, reports concerning laterality of emotion point to a left hemisphere advantage for complex emotion versus a right hemisphere advantage for basic emotions (the "type hypothesis"). In this study, we investigated the lateralization of basic versus complex (negative and positive) eye expressions in adults with AS in 2 consecutive experiments: in the first experiment, the performance of AS and healthy controls were compared in a divided visual field task. In the second experiment, the ability of participants with AS to identify eye expressions varying in valence and type was compared with that of patients with localized lesions in either the right or the left hemispheres. Controls were better in recognizing negative emotions presented to the left visual field and positive emotions presented to the right visual field, whereas individuals with AS failed to show this interaction effect. Lateralization of basic versus complex emotions was less evident although indeed controls identified better basic emotions presented to the right visual field. Furthermore, participants with AS exhibited a similar pattern of recognition of negative versus positive emotions to that of patients with left hemisphere damage. It is suggested that the pattern of performance of individuals with AS resembles that of patients with left hemisphere dysfunction.