Abstract
Many studies have been carried out into both motor and sensory laterality of horses in agonistic and stressful situations. Here we examine sensory laterality in affiliative interactions within four groups of domestic horses and ponies (N = 31), living in stable social groups, housed at a single complex close to Vienna, Austria, and demonstrate for the first time a significant population preference for the left side in affiliative approaches and interactions. No effects were observed for gender, rank, sociability, phenotype, group, or age. Our results suggest that right hemisphere specialization in horses is not limited to the processing of stressful or agonistic situations, but rather appears to be the norm for processing in all social interactions, as has been demonstrated in other species including chicks and a range of vertebrates. In domestic horses, hemispheric specialization for sensory input appears not to be based on a designation of positive versus negative, but more on the perceived need to respond quickly and appropriately in any given situation.
Highlights
Specialization in the functions of the two hemispheres of the brain has been well catalogued and is believed to have its origins in brain asymmetry in early vertebrates (MacNeilage et al 2009)
The specific questions we addressed were: (1) is sensory laterality in affiliative interactions normally distributed, or is one side preferred over the other; (2) if there is a side preference, is this affected by age, rank, sociability, gender, or phenotype of the individuals; (3) if there is a side preference, is it affected by the social composition of the group?
There was a weak trend for the riding horses to be more strongly lateralised (Wilcoxon rank sum test: N = 31, W = 65, p = 0.09) and this is illustrated in Fig. 2 in the supplementary material
Summary
Specialization in the functions of the two hemispheres of the brain has been well catalogued and is believed to have its origins in brain asymmetry in early vertebrates (MacNeilage et al 2009). There is increasing interest in the details of asymmetry of brain function and the different ways in which information is processed and interpreted by each hemisphere. Asymmetry has been observed in many taxa, including mammals, birds, fish, and even insects (for overview see Rogers 2017), and may be expressed as motor.
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