Abstract: Research on a growing number of vertebrate species has shown that the left and right sides of the brain process information in different ways and that lateralized brain function is expressed in both specific and broad aspects of behaviour. This paper reviews the available evidence relating strength of lateralization to behavioural/cognitive performance. It begins by considering the relationship between limb preference and behaviour in humans and primates from the perspectives of direction and strength of lateralization. In birds, eye preference is used as a reflection of brain asymmetry and the strength of this asymmetry is associated with behaviour important for survival (e.g., visual discrimination of food from non-food and performance of two tasks in parallel). The same applies to studies on aquatic species, mainly fish but also tadpoles, in which strength of lateralization has been assessed as eye preferences or turning biases. Overall, the empirical evidence across vertebrate species points to the conclusion that stronger lateralization is advantageous in a wide range of contexts. Brief discussion of interhemispheric communication follows together with discussion of experiments that examined the effects of sectioning pathways connecting the left and right sides of the brain, or of preventing the development of these left-right connections. The conclusion reached is that degree of functional lateralization affects behaviour in quite similar ways across vertebrate species. Although the direction of lateralization is also important, in many situations strength of lateralization matters more. Finally, possible interactions between asymmetry in different sensory modalities is considered.

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.

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.

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.

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.