Hemispheric asymmetries for emotions in non-human primates: A systematic review.

A systematic review of investigations evaluating hemispheric asymmetries for emotions in primates was undertaken to individuate the most consistent lines of research allowing to check the hypothesis of a continuum in emotional lateralization across vertebrates. We reviewed studies on the lateralization of emotional expression (N = 31) and perception (N = 32) and of markers of emotional activation (N = 9), trying to distinguish those which had given respectively more consistent or more conflicting outcomes. Furthermore, we tried to identify the most strongly supported model of emotional lateralization. The most consistent results were obtained in studies investigating asymmetries in emotional expression at the facial level and in the perception of emotional facial expressions, whereas the most disappointing data were obtained in investigations evaluating possible neurophysiological markers of lateralized emotional activation. These results supported more the hypothesis of a continuity between humans and non-human primates than the more general hypothesis of a continuum between humans and all vertebrates. Furthermore, results supported more the 'right hemisphere' than the 'valence' model of emotional lateralization.