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Lucidi, P., Bacco, G., Sticco, M., Mazzoleni, G., Benvenuti, M., Bernabò, N., et al. (2013). Assessment of motor laterality in foals and young horses (Equus caballus) through an analysis of derailment at trot. Physiol. Behav., 109, 8–13.
Abstract: The conflicting results regarding the study of motor laterality in horses may indicate that there does not exist a proper method to assess the degree and the direction of motor bias in these animals. Unfortunately, even less is known about the development of laterality in horses, and to what extent early manipulations can still exert their effects in adulthood. We propose a new method that can be easily applied at a very early age thus avoiding testing adult horses eventually biased by human handling and/or training. Forty-six horses (29 nine-month-old foals and 17 two-year old horses) were handled since birth bilaterally and housed in groups in wide areas. At the time of the analysis, in order to minimize environmental and sensorial disturbances, each horse was tested in a round pen individually or as dyad mother-foal. The ability/inability to properly execute a circle at trot was then recorded, assuming the direction of derailment, i.e. the cutting of the circle, as an indicator of motor bias. From the results of the study it is arguable that motor laterality in horses is acquired over time: in fact foals tested while their mothers were being subjected to longeing showed a higher percentage of ambidextrous animals, while two-year-old horses appeared biased toward the right (p<0.05). Results are discussed in the light of the scientific knowledge about equine biomechanics, taking into account horses' locomotion that leads to the advancement of the body mass through the activation of a kinetic chain that originates from the hindquarters.
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Komárková, M., & Bartošová, J. (2012). Lateralized suckling in domestic horse foals (Equus caballus). In K. Krueger (Ed.), Proceedings of the 2. International Equine Science Meeting (Vol. in press). Wald: Xenophon Publishing.
Abstract: Animals with eyes placed laterally on their head would respond differently to stimuli detected on their different sides. Visual cues from the left eye are processed in the right hemisphere which controls the intensive emotion expression and fast response to the stimuli, while the left hemisphere receiving the information from the contralateral eye is responsible for the routine behaviour and concentration. Different use of left/right eye for exploring environment and evaluation of different stimuli was recently described in domestic horses. They use left eye predominantly for watching novel object or frightening stimulus which indicates specialization of right hemisphere (RH) for appraisal of these types of stimuli. We presumed such lateralisation also in foals during suckling when only monocular vision can be employed for observing surroundings (foals suck mostly in antiparallel body position). Two mutually exclusive hypotheses about the origin of probable foal’s preference for particular suckling side were postulated: 1) visual lateralization, then the foals should suck more often from the mother’s right side (‘from right’), so as potential danger would be detected by the better adapted right hemisphere (i.e. left eye); 2) motor lateralization (the analogous concept as human “handness”), then a foal should suck predominantly from one side, either left or right, more often. Within two seasons, suckling behaviour of 59 Kladruby mares giving birth to 79 foals was observed from deliveries to abrupt weaning (4-7 months of age). From 10 607 recorded suckling solicitations, 50.2% were performed from right, thus there was no preference of the suckling side on a population level. However, we found large variability in the probability of suckling from right among individual foals (p<0.0001); the probability ranged from 0.22-0.98. One third of the foals (35.4%) showed strong, either right (N=13) or left (N=15) side preference which further strengthened with age (interaction suckling side preference*foal’s age: p<0.0001). Other tested variables, i.e. sex of the foal, age of the mother and identity of the herd were not significant. The probability that the mother rejected foal’s suckling solicitation (N=108) did not differ according to the suckling side (right/left) or suckling side preference (right/left/no preference). Suckling bout duration was not significantly influenced neither by the suckling side nor suckling side preference regardless the mother or the foal terminated the suckling bout. In conclusion, only 16 % of the foals revealed significant right side preference for suckling while 19 % left side and 65 % no preference. Thus, we can reject the visual hypothesis because a general trait to suck with left eye open for better danger detection and recognition is unlikely to occur, at least in up to 7 months old foals. Such a young foal is probably fully focused on suckling and relies on mother’s vigilance. Observed individual side preferences indicated more likely a kind of motor lateralization in part of the foals. Further research is needed to clear up the effects of age and individual experience of the foal. Supported by AWIN, EU FP7 project No. 266213.
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Cowell, P. E., Fitch, R. H., & Denenberg, V. H. (1999). Laterality in animals: relevance to schizophrenia. Schizophr Bull, 25(1), 41–62.
Abstract: Anomalies in the laterality of numerous neurocognitive dimensions associated with schizophrenia have been documented, but their role in the etiology and early development of the disorder remain unclear. In the study of normative neurobehavioral organization, animal models have shed much light on the mechanisms underlying and the factors affecting adult patterns of both functional and structural asymmetry. Nonhuman species have more recently been used to investigate the environmental, genetic, and neuroendocrine factors associated with developmental language disorders in humans. We propose that the animal models used to study the basis of lateralization in normative development and language disorders such as dyslexia could be modified to investigate lateralized phenomena in schizophrenia.
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