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Tomkins, L. M., McGreevy, P. D., & Branson, N. J. (2010). Lack of standardization in reporting motor laterality in the domestic dog (Canis familiaris). Journal of Veterinary Behaviour, 5(5), 235–239.
Abstract: Over the past 2 decades, numerous studies have been undertaken to assess motor laterality in the domestic dog. In anticipation of growth in this area of enquiry, we decided to review the literature on canine motor biases to identify any shortcomings, reflect on the lessons to be learned from and offer ways forward for future research into canine laterality. The aim of this review is to (i) summarize motor laterality findings in the dog, (ii) highlight areas lacking in standardization, and (iii) propose necessary criteria for future tests and global reporting protocols. Our review of the literature highlighted the lack of standardization between studies in task selection, sample size, number of behavior scores recorded, and the methods by which motor laterality were classified and reported. This review illustrates the benefits of standardizing methods of motor laterality assessment so that comparisons can be made between the populations sampled. By adopting such an approach, researchers should mutually benefit as motor laterality data could then be compared and subjected to meta-analysis.
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Tomkins, L. M., Williams, K. A., Thomson, P. C., & McGreevy, P. D. (2010). Sensory Jump Test as a measure of sensory (visual) lateralization in dogs (Canis familiaris). Journal of Veterinary Behavior, 5(5), 256–267.
Abstract: Sensory lateralization in dogs (n = 74) was investigated in this study using our innovation, the Sensory Jump Test. This required the modification of head halters to create three different ocular treatments (binocular, right, and left monocular vision) for eye preference assessment in a jumping task. Ten jumps were recorded as a jump set for each treatment. Measurements recorded included (i) launch and landing paws, (ii) type of jump, (iii) approach distance, (iv) clearance height of the forepaw, hindpaw, and the lowest part of the body to clear the jump, and (v) whether the jump was successful. Factors significantly associated with these jump outcomes included ocular treatment, jump set number, and replication number. Most notably, in the first jump set, findings indicated a left hemispheric dominance for the initial navigation of the Sensory Jump Test, as left monocular vision (LMV) compromised of jumping more than right monocular (RMV) and binocular vision, with a significantly reduced approach distance and forepaw clearance observed in dogs with LMV. However, by the third jump set, dogs undergoing LMV launched from a greater approach distance and with a higher clearance height, corresponding to an increase in success rate of the jump, in comparison with RMV and binocular vision dogs. A marginally non-significant RMV bias was observed for eye preference based on the laterality indices for approach distance (P = 0.060) and lowest body part clearance height (P = 0.067). A comparison between eye preference and launching or landing paws showed no association between these measures of sensory and motor laterality. To our knowledge, this is the first study to report on sensory lateralization in the dog, and furthermore, to compare both motor and sensory laterality in dogs.
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Batt, L. S., Batt, M. S., Baguley, J. A., & McGreevy, P. D. (2009). The relationships between motor lateralization, salivary cortisol concentrations and behavior in dogs. Journal of Veterinary Behaviour, 4(6), 216–222.
Abstract: The degree of lateralization (LI) indicates both the direction and strength of a paw preference. Here, a positive value is indicative of a right paw bias, and a negative value of a left paw bias. Higher numbers on the positive side of the scale and lower numbers on the negative side of the scale indicate a greater strength of that lateralization. The strength of motor lateralization (|LI|) is the absolute value of the LI. The use of absolute value removes directionality (i.e., does not indicate left or right paw bias) and instead indicates only the strength of the paw preference. Both LI and |LI| have been associated with behavioral differences in a range of species. The assessment of motor lateralization in the dog can be conducted by observing the paw used to perform motor tasks. Elevated cortisol concentrations have been associated with fearfulness in many species. Additionally, fearfulness and boldness can be assessed in response to so-called temperament tests. Consequently, in this study we examine the relationship between lateralization, temperament test results, and cortisol concentrations in 43 potential guide dogs, of which 38 were Labrador retrievers and 5 were golden retrievers. Over a 14-month period, the current study assessed motor lateralization and salivary cortisol concentrations 3 times (approximately 6 months of age, 14 months of age, and after the dogs' performance in the guide dog program had been determined) and behavior twice (approximately 6 and 14 months of age). This study is the first to examine the relationship between behavior, lateralization, and cortisol concentrations in dogs. It implemented an objective and quantifiable assessment of behavior that may be of use to a variety of dog-focused stakeholders. Findings show that during the Juvenile testing period (6 months of age), dogs with higher cortisol concentrations were typically less able to rest when exposed to the unfamiliar testing room. Results from both Juvenile and Adult Test (14 months of age) periods showed that a greater |LI| and LI were associated with more confident and relaxed behavior when dogs were exposed to novel stimuli and unfamiliar environments. Significant elevations of cortisol concentrations were found at the completion of guide dog training when compared with results from the 2 prior test periods. This finding may reflect maturation or the effect of the prolonged kenneling which occurred during this period.
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Reddon, A. R., & Hurd, P. L. (2009). Acting unilaterally: Why do animals with strongly lateralized brains behave differently than those with weakly lateralized brains? Bioscience Hypotheses, 2(6), 383–387.
Abstract: Cerebral lateralization was once thought to be unique to humans, but is now known to be widespread among the vertebrates. Lateralization appears to confer cognitive advantages upon those that possess it. Despite the taxonomic ubiquity and described advantages of lateralization, substantial individual variation exists in all species. Individual variation in cerebral lateralization may be tied to individual variation in behaviour and the selective forces that act to maintain variation in behaviour may also act to maintain variation in lateralization. The mechanisms linking individual variation in the strength of cerebral lateralization to individual variation in behaviour remain obscure. We propose here a general hypothesis which may help to explain this link. We suggest that individuals with strong and weak lateralizations behave differently because of differences in the ability of one hemisphere to inhibit the functions of the other in each type of brain organization. We also suggest a specific mechanism involving the asymmetric epithalamic nucleus, the habenula. We conclude by discussing some predictions and potential tests of our hypothesis.
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Austin, N. P., & Rogers, L. J. (2014). Lateralization of agonistic and vigilance responses in Przewalski horses (Equus przewalskii). Applied Animal Behaviour Science, 151, 43–50.
Abstract: tEye and limb preferences were scored in the closest undomesticated relative of Equuscaballus using the same methods as used previously to study laterality in feral horses.Observations were made of 33 Przewalski horses (Equus ferus przewalskii) (male N = 20,female N = 13) living under natural social conditions on a large reserve in France. Signifi-cant left-eye/side biases were found in agonistic interactions within harem bands (M ± SEbias to left 58% ± 0.01 for threats, P < 0.001; 68% ± 0.05 for attacks; P < 0.001) and in stallionfights (threats, 52% ± 0.01 left, P < 0.001; attacks, 63% ± 0.02 left, P < 0.001): as many as 80%of the horses were significantly lateralized in attack responses within harem bands. Lat-erality of vigilance was measured as lifting up the head from grazing and turning it to theleft or right side: a directional bias to the left was found (M ± SE 53% ± 0.02 left, P < 0.001).Side bias in reactivity was calculated as the percent of head lifts above the level of thewithers on the left or right side and this was also left side biased (M ± SE 73% ± 0.03 left,P < 0.001). These results indicate right-hemisphere specialization for control of aggressionand responses to novelty. The left bias in attack scores within harem bands was strongerin males than females (P = 0.024) and in immature than adult horses (P = 0.032). Immaturehorses were also more strongly lateralized than adults in vigilance scores (P = 0.022), whichmay suggest that experience reduces these side biases. Our results show that Przewalskihorses exhibit left eye preferences, as do feral horses, and do so even more strongly thanferal horses. Considering feral and Przewalski horses together, we deduce that ancestralhorses had similar lateral biases. Also similar to feral horses, the Przewalski horses showedno significant forelimb preference at the group level or in the majority of horses at theindividual level, confirming the hypothesis that previously reported limb preferences indomestic breeds are entrained or generated by breed-specific selection.
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Shen, Y. - Q., Hebert, G., Lin, L. - Y., Luo, Y. - L., Moze, E., Li, K. - S., et al. (2005). Interleukine-1β and interleukine-6 levels in striatum and other brain structures after MPTP treatment: influence of behavioral lateralization. Journal of Neuroimmunology, 158(1–2), 14–25.
Abstract: MPTP (N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) induces diminution of the dopamine in nigrostriatal pathway and cognitive deficits in mice. MPTP treatment also increases pro-inflammatory cytokine production in substantia nigra and striatum. Since, pro-inflammatory cytokines influence striatal dopamine content and provoke cognitive impairments, the cognitive defects induced by MPTP may be partly due to brain cytokine induction in other structures than nigrostriatal pathway. Furthermore, behavioral lateralization, as assessed by paw preference, influences cytokine production at the periphery and in the central nervous system. Behavioral lateralization may thus influence brain cytokine levels after MPTP. In order to address these issues, mice selected for paw preference were injected with 25 mg/kg MPTP i.p. for five consecutive days after which striatal dopamine and DOPAC contents were measured by HPLC and IL-1β and IL-6 quantified by ELISA in the striatum, cerebral cortex, hippocampus and hypothalamus. The results showed that MPTP treatment induced dramatic loss of DA in striatum, simultaneously, IL-6 levels decreased in the striatum and increased in hippocampus and hypothalamus, while IL-1β levels decreased in the striatum, cerebral cortex and hippocampus. Interestingly, striatal dopamine turnover under basal conditions as well as striatal IL-1β and IL-6 levels under basal conditions and after MPTP depended on behavioral lateralization. Left pawed mice showed a higher decrease in dopamine turnover and lower cytokine levels as compared to right pawed animals. Behavioral lateralization also influenced IL-6 hippocampal levels under basal conditions and IL-1β cortical levels after MPTP. From these results, it can be concluded that MPTP-induced cognitive defects are accompanied by an alteration of pro-inflammatory cytokine levels in brain structures other than those involved in the nigrostriatal pathway. In addition, MPTP-induced dopamine decrease is influenced by behavioral lateralization, possibly through an effect on brain cytokine levels.
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Siniscalchi, M., Sasso, R., Pepe, A. M., Dimatteo, S., Vallortigara, G., & Quaranta, A. (2010). Catecholamine plasma levels following immune stimulation with rabies vaccine in dogs selected for their paw preferences. Neuroscience Letters, 476(3), 142–145.
Abstract: Epinephrine and norepinephrine plasma levels were assessed in dogs in relation to paw preference following an immune challenge with rabies vaccine. The results showed that both catecholamines increased after the vaccine administration, confirming the main role of the sympathetic nervous system in the modulation activity between the brain and the immune system. Moreover, ambidextrous dogs showed a significantly higher increase of epinephrine levels 8 days after immunization with respect to right- and left-pawed dogs, suggesting that the biological activity of this molecule could be key for a different immune response with regard to laterality.
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Phillips, C. J. C., Oevermans, H., Syrett, K. L., Jespersen, A. Y., & Pearce, G. P. (2015). Lateralization of behavior in dairy cows in response to conspecifics and novel persons. Journal of Dairy Science, 98(4), 2389–2400.
Abstract: Abstract The right brain hemisphere, connected to the left eye, coordinates fight and flight behaviors in a wide variety of vertebrate species. We investigated whether left eye vision predominates in dairy cows’ interactions with other cows and humans, and whether dominance status affects the extent of visual lateralization. Although we found no overall lateralization of eye use to view other cows during interactions, cows that were submissive in an interaction were more likely to use their left eye to view a dominant animal. Both subordinate and older cows were more likely to use their left eye to view other cattle during interactions. Cows that predominantly used their left eye during aggressive interactions were more likely to use their left eye to view a person in unfamiliar clothing in the middle of a track by passing them on the right side. However, a person in familiar clothing was viewed predominantly with the right eye when they passed mainly on the left side. Cows predominantly using their left eyes in cow-to-cow interactions showed more overt responses to restraint in a crush compared with cows who predominantly used their right eyes during interactions (crush scores: left eye users 7.9, right eye users 6.4, standard error of the difference = 0.72). Thus, interactions between 2 cows and between cows and people were visually lateralized, with losing and subordinate cows being more likely to use their left eyes to view winning and dominant cattle and unfamiliar humans.
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Marinsek, N. L., Gazzaniga, M. S., & Miller, M. B. (2016). Chapter 17 – Split-Brain, Split-Mind. In S. Laureys, O. Gosseries, & G. Tononi (Eds.), The Neurology of Conciousness (Second Edition) (pp. 271–279). San Diego: Academic Press.
Abstract: The corpus callosum anatomically and functionally connects the two cerebral hemispheres. Despite its important role in interhemispheric communication however, severing the corpus callosum produces few--if any--noticeable cognitive or behavioral abnormalities. Incredibly, split-brain patients do not report any drastic changes in their conscious experience even though nearly all interhemispheric communication ceases after surgery. Extensive research has shown that both hemispheres remain conscious following disconnection and the conscious experience of each hemisphere is private and independent of the other. Additionally, the conscious experiences of the hemispheres appear to be qualitatively different, such that the consciousness of the left hemisphere is more enriched than the right. In this chapter, we offer explanations as to why split-brain patients feel unified despite possessing dual conscious experiences and discuss how the divided consciousness of split-brain patients can inform current theories of consciousness.
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Reddon, A. R., & Hurd, P. L. (2009). Individual differences in cerebral lateralization are associated with shy-bold variation in the convict cichlid. Anim. Behav., 77(1), 189–193.
Abstract: Cerebral lateralization, the preferential use of one hemisphere of the brain to perform certain cognitive functions, is a widespread and evolutionarily ancient adaptation. Lateralization appears to enhance cognitive capacity, yet substantial individual variation in the strength cerebral lateralization is apparent in all species studied so far. It is puzzling that cerebral lateralization, a seemingly advantageous trait, has not been driven to fixation. It has been suggested that variation in lateralization may be linked to individual variation in behaviour, which itself may be subject to disruptive selection. We examined the relation between cerebral lateralization and individual variation in boldness in the convict cichlid, Archocentrus nigrofasciatus. We show that convict cichlids that are more strongly lateralized when exploring a familiar environment, but not a novel one, are quicker to emerge from a shelter in a test for boldness. The possibility that cerebral lateralization is linked to life history strategy is discussed.
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