Emotion: An evolutionary model of lateralization in the human brain

Since several reviews have recently discussed the lateralization of emotions, this chapter will take into account the possible evolutionary meaning of this lateralization. The organization of the chapter will be based on the following steps. I will first propose that emotions must be considered as a complex adaptive system, complementary to the more phylogenetically advanced cognitive system. Second, I will remind historical aspects and consolidated results on the lateralization of emotions. Then I will discuss the phylogenetic aspects of the problem, trying to evaluate if emotional asymmetries concern only humans and some nonhuman primates or are part of a continuum between humans and many phylogenetically distant animal species. After having reviewed various aspects of emotional lateralization across different animal species and (more specifically) in nonhuman primates, I will propose a general model of hemispheric asymmetries in the human brain, based on theoretical models and empiric data. Theoretical models stem from the influence that the presence or the absence of language can have on concomitant hemispheric functions, whereas supporting neuropsychologic data have been gathered in patients with unilateral brain damage.