Bottlenose dolphins' (Tursiops Truncatus) visual and motor laterality depending on emotional contexts

Hemispheric lateralization is a specialized neural and cognitive processing achieved preferentially by either the left or the right hemisphere of the brain. Among vertebrates, emotions processing seems to be lateralized, but the involvement of each hemisphere is still on debate. Our study investigated visual and motor laterality on five bottlenose dolphins' (Tursiops truncatus) during spontaneous and experimentally induced emotional contexts. We measured motor laterality in pectoral used and swimming position during positive social interactions. Additionally, during training sessions, stimuli with positive or negative emotional valences were presented either on the dolphins' left or right side. Emotional reactions toward stimuli were measured and a visual laterality index was calculated. Dolphins were visually left-lateralized during training sessions. They also reacted more when negative stimuli were presented on their left side than right side during the first stimuli presentation. Our results suggest that bottlenose dolphins, like other vertebrates, may present a right hemisphere dominance for social information processing, detection of and response to unpredictable or novel stimuli and a left-hemisphere dominance during escape responses inhibition. Further studies on a larger sample size should explore inter-individual variation and identify other potential contexts in which lateralization emerges. Emotional lateralization should be considered as a potential indicator for future dolphin welfare assessment.