Low survival of strongly footed pheasants may explain constraints on lateralization

Limb preferences in non-human vertebrates: A new decade

Over a decade ago, we demonstrated that population-level asymmetries in limb preferences are not uniquely human but occur in various species of non-human animals (Ströckens, F., Güntürkün, O., & Ocklenburg, S. (2013). Limb preferences in non-human vertebrates. Laterality, 18(5), 536-575). While back then, vertebrate limb preference data were too scarce to reconstruct the evolutionary basis of human handedness or apply phylogenetic comparative methods, many voids were filled in the meantime. It is therefore high time to update the last analysis on limb preferences in all non-extinct vertebrate orders in the present article. We show that the robustness of empirical evidence for limb preference in non-human vertebrates increased in the last decade due to (1) more studies, (2) larger sample sizes, and (3) an increased number of meta-analyses integrating findings from various species (e.g., cats, dogs, rats, mice). Similar to the previous publication, we used cladographic comparisons to systematically assess limb preferences in non-extinct vertebrate orders. The identified studies analyzed 172 different species. Overall, 39.53% of species showed evidence for population-level asymmetries, 32.56% showed individual-level asymmetries, and 27.91% showed no asymmetry. These findings not only further support the notion that asymmetries are a widespread feature of vertebrate motor organization, but they also identify crucial gaps that should be filled by future investigations.

Brain and behavioral asymmetries in nonprimate species

Brain and behavioral asymmetries are widespread across the animal kingdom, suggesting that even simpler nervous systems benefit from such features. In the last 30 years, research conducted on several vertebrate (but also invertebrate) animal models has massively contributed to our understanding of the causation, development, evolution, and function of lateralization. Here, we review some of this research, highlighting the importance of studying this topic in nonprimate species for a deeper understanding of the mechanisms behind cerebral asymmetries. We report evidence of handedness and motor asymmetries as well as the results of research on perceptual and cognitive asymmetries in nonprimate animals, analyzing the contribution of such studies in the research field of cerebral asymmetries.

The repeatability of behavioural laterality during nest building in zebra finches

Cerebral laterality is a widespread phenomenon across animals and refers to the specialization of the left and right hemispheres of the brain for perceptual, cognitive and behavioural tasks. Behavioural laterality occurs in several contexts, including foraging, mate selection, predator detection and tool manufacture. Behavioural laterality during nest building, however, has rarely been addressed. We conducted two experiments to examine (1) whether behavioural laterality occurs during nest building, (2) whether laterality correlates with nest-building speed, (3) whether laterality during nest building is repeatable, and (4) whether nest-building experience influences laterality. In Experiment 1, we scored individual laterality indices for 58 zebra finch (Taeniopygia guttata) males, the nest-building sex in this species, based on which eye he used to view then select the first 25 pieces of nest material. We calculated correlations between laterality strength and nest-building duration. In Experiment 2, to test the repeatability of laterality during nest building, we measured laterality for 20 males across five nests built by each male. Individuals varied both in the direction and the strength of behavioural laterality of material selection during nest building. Overall, however, males were not consistent in their laterality across the five nests. We found no correlation between laterality strength and nest-building duration in either experiment. Finally, we found evidence for building experience influencing the behavioural laterality of individuals: more building experience results in more predictable behavioural laterality during nest-material selection.

Motor-sensory biases are associated with cognitive and social abilities in humans

Across vertebrates, adaptive behaviors, like feeding and avoiding predators, are linked to lateralized brain function. The presence of the behavioral manifestations of these biases are associated with increased task success. Additionally, when an individual's direction of bias aligns with the majority of the population, it is linked to social advantages. However, it remains unclear if behavioral biases in humans correlate with the same advantages. This large-scale study (N = 313-1661, analyses dependent) examines whether the strength and alignment of behavioral biases associate with cognitive and social benefits respectively in humans. To remain aligned with the animal literature, we evaluate motor-sensory biases linked to motor-sequencing and emotion detection to assess lateralization. Results reveal that moderate hand lateralization is positively associated with task success and task success is, in turn, associated with language fluency, possibly representing a cascade effect. Additionally, like other vertebrates, the majority of our human sample possess a 'standard' laterality profile (right hand bias, left visual bias). A 'reversed' profile is rare by comparison, and associates higher self-reported social difficulties and increased rate of autism and/or attention deficit hyperactivity disorder. We highlight the importance of employing a comparative theoretical framing to illuminate how and why different laterization profiles associate with diverging social and cognitive phenotypes.

Effect of visual lateralization on the spatial position of individuals within a school of oval squid (Sepioteuthis lessoniana)

The spatial position of individuals within a social group, which provides the group members with benefits and costs, is determined by several physical and physiological factors. Lateralization (left and right asymmetry of morphology and behavior) could also be factors determining the individual's positions within a group. However, this possibility has been documented in some fish species, but never in an invertebrate species. This study investigates the association between spatial positions and lateralization in oval squid, Sepioteuthis lessoniana, which displays social behavior, such as schooling and lateralization for eye use (visual lateralization). The direction and strength of visual lateralization were determined for single squid by observing which eye was used to detect the prey, predators, and conspecifics. The spatial positions of individuals were determined by identifying whether the squids were in the left or right side from the center of the school. When the prey was presented to schooling squids, strongly lateralized squids against prey positioned themselves on the right side, whereas weakly lateralized squids positioned themselves on the left side. When the predator was presented to squids, the strongly lateralized squids against the conspecifics positioned themselves on the right side, and the weakly lateralized squids positioned themselves on the left side. When no targets were presented, the strongly lateralized squids against the predator positioned themselves on the right side, whereas the weakly lateralized squids positioned themselves on the left side. The strength of visual lateralization of oval squid could offer the defensive and offensive functions of schools with specific individual positions.

Brain Lateralization and Cognitive Capacity

One way to increase cognitive capacity is to avoid duplication of functions on the left and right sides of the brain. There is a convincing body of evidence showing that such asymmetry, or lateralization, occurs in a wide range of both vertebrate and invertebrate species. Each hemisphere of the brain can attend to different types of stimuli or to different aspects of the same stimulus and each hemisphere analyses information using different neural processes. A brain can engage in more than one task at the same time, as in monitoring for predators (right hemisphere) while searching for food (left hemisphere). Increased cognitive capacity is achieved if individuals are lateralized in one direction or the other. The advantages and disadvantages of individual lateralization are discussed. This paper argues that directional, or population-level, lateralization, which occurs when most individuals in a species have the same direction of lateralization, provides no additional increase in cognitive capacity compared to individual lateralization although directional lateralization is advantageous in social interactions. Strength of lateralization is considered, including the disadvantage of being very strongly lateralized. The role of brain commissures is also discussed with consideration of cognitive capacity.

Paw preferences in mice and rats: Meta-analysis

Mice and rats are among the most common animal model species in both basic and clinical neuroscience. Despite their ubiquity as model species, many clinically relevant brain-behaviour relationships in rodents are not well understood. In particular, data on hemispheric asymmetries, an important organizational principle in the vertebrate brain, are conflicting as existing studies are often statistically underpowered due to small sample sizes. Paw preference is one of the most frequently investigated forms of hemispheric asymmetries on the behavioural level. Here, we used meta-analysis to statistically integrate findings on paw preferences in rats and mice. For both species, results indicate significant hemispheric asymmetries on the individual level. In mice, 81 % of animals showed a preference for either the left or the right paw, while 84 % of rats showed this preference. However, contrary to what has been reported in humans, population level asymmetries were not observed. These results are particularly significant as they point out that paying attention to potential individual hemispheric differences is important in both basic and clinical neuroscience.

No evidence that footedness in pheasants influences cognitive performance in tasks assessing colour discrimination and spatial ability

The differential specialization of each side of the brain facilitates the parallel processing of information and has been documented in a wide range of animals. Animals that are more lateralized as indicated by consistent preferential limb use are commonly reported to exhibit superior cognitive ability as well as other behavioural advantages. We assayed the lateralization of 135 young pheasants (Phasianus colchicus), indicated by their footedness in a spontaneous stepping task, and related this measure to individual performance in either 3 assays of visual or spatial learning and memory. We found no evidence that pronounced footedness enhances cognitive ability in any of the tasks. We also found no evidence that an intermediate footedness relates to better cognitive performance. This lack of relationship is surprising because previous work revealed that pheasants have a slight population bias towards right footedness, and when released into the wild, individuals with higher degrees of footedness were more likely to die. One explanation for why extreme lateralization is constrained was that it led to poorer cognitive performance, or that optimal cognitive performance was associated with some intermediate level of lateralization. This stabilizing selection could explain the pattern of moderate lateralization that is seen in most non-human species that have been studied. However, we found no evidence in this study to support this explanation.

Learning is negatively associated with strength of left/right paw preference in wild grey squirrels (Sciurus carolinensis)

Cerebral laterality, via hemispheric specialisation, has been evidenced across the animal kingdom and linked to cognitive performance in a number of species. Previously it has been suggested that cognitive processing is more efficient in brains with stronger hemispheric differences in processing, which may be the key fitness benefit driving the evolution of laterality. However, evidence supporting a positive association between cognitive performance and lateralization is mixed: data from studies of fish and birds show a positive relationship whereas more limited data from studies of mammals suggest a weak or even negative relationship, suggesting the intriguing possibility of a mammal/non-mammal divide in the nature of this relationship. Here, we report an empirical test examining the relationship between lateralization and cognitive performance in wild grey squirrels (Sciurus carolinensis) by measuring left/right paw preference as a behavioural assay of cerebral lateralization and learning speed as an assay of cognitive efficiency. We carried out a motor-based laterality test using a reaching paradigm and measured learning speed on a problem-solving task. In accordance with the suggestion of a mammal/non-mammal divide, we found a negative relationship between strength of paw preference and performance on the learning task. We discuss this finding in light of niche-specific adaptations, task-specific demands and cognitive flexibility.

Individual-Level and Population-Level Lateralization: Two Sides of the Same Coin

Lateralization, i.e., the different functional roles played by the left and right sides of the brain, is expressed in two main ways: (1) in single individuals, regardless of a common direction (bias) in the population (aka individual-level lateralization); or (2) in single individuals and in the same direction in most of them, so that the population is biased (aka population-level lateralization). Indeed, lateralization often occurs at the population-level, with 60–90% of individuals showing the same direction (right or left) of bias, depending on species and tasks. It is usually maintained that lateralization can increase the brain’s efficiency. However, this may explain individual-level lateralization, but not population-level lateralization, for individual brain efficiency is unrelated to the direction of the asymmetry in other individuals. From a theoretical point of view, a possible explanation for population-level lateralization is that it may reflect an evolutionarily stable strategy (ESS) that can develop when individually asymmetrical organisms are under specific selective pressures to coordinate their behavior with that of other asymmetrical organisms. This prediction has been sometimes misunderstood as it is equated with the idea that population-level lateralization should only be present in social species. However, population-level asymmetries have been observed in aggressive and mating displays in so-called “solitary” insects, suggesting that engagement in specific inter-individual interactions rather than “sociality” per se may promote population-level lateralization. Here, we clarify that the nature of inter-individuals interaction can generate evolutionarily stable strategies of lateralization at the individual- or population-level, depending on ecological contexts, showing that individual-level and population-level lateralization should be considered as two aspects of the same continuum.