The emergence of emotional lateralization: Evidence in non-human vertebrates and implications for farm animals

The study and protection of animal welfare are based on the assumption that animals are sentient beings, capable of experiencing emotions. Still, our understanding of animal emotions is limited. In this review we focus on the potential of cerebral-lateralization research to provide new insights into animal emotional processing. Thereby, our aims were, first, to find a universal lateralization pattern in emotional processing across vertebrates and, second, to discuss how knowledge of emotional-lateralization patterns can be used in science and practice to contribute to improve farm-animal welfare. A literature review suggests evidence of lateralized functioning during emotional contexts across the vertebrate classes, from early vertebrates such as fish and amphibians to non-human primates. With the possible exception of fish, all vertebrate classes seem to show a similar lateralization pattern for emotional processing, with a right-hemisphere dominance for processing rather negatively connotated emotions, such as fear and aggression, and a left-hemisphere dominance for processing positively connotated emotions, such as those elicited by a food reward. Thus, both hemispheres are involved in emotional processing and hemispheric dominance may be used as an indicator of emotional valence (negative-positive). Although only a few domestic animal species (e.g. chicken, sheep, dog and horse) have been extensively studied with regard to emotional lateralization, evidence gathered so far suggests that the right-hemisphere dominance for fear and aggression and left-hemisphere dominance in responses to food rewards also applies to these species. Such patterns could be exploited in animal welfare studies to gain insight into how an animal experiences a potentially emotional situation and to improve farm-animal management. Further research should focus on rarely-studied species and on rarely-studied emotional contexts, such as sex and positive social situations, to improve our understanding of animal emotional lateralization. (C) 2013 Elsevier B.V. All rights reserved.