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Crustaceans are increasingly used as research subjects in experiments investigating learning in invertebrates. While many of these species may be useful models it is essential to document the presence or absence of behavioral laterality, especially considering the long-held belief that functional lateralization was unique to humans or other vertebrate species. Neglecting this fundamental step weakens the applicability of results and may unnecessarily complicate experimental design. Amphipods (Gammarus pseudolimnaeus) may be a useful invertebrate for studying simple discriminations or escape behavior, but research on their potential behavioral laterality is absent. The current study investigated whether amphipods demonstrate a left-right bias when navigating an aquatic T-maze by placing them in the maze and recording their choices across multiple trials. Our results suggested that amphipods do not show a strong left-right bias during initial navigation of an aquatic T-maze. These findings may encourage other researchers to test invertebrates for behavioral laterality, utilize amphipods in studies of simple forms of learning, and potentially simplify future experimental design. • Amphipods show no left/right arm preference on first exposure to an aquatic T-maze. • Amphipods show no bias in choice of same or different arm across days of testing. • T-maze orientation did not impact amphipod arm choice. [ABSTRACT FROM AUTHOR]

The left-cradling bias (i.e., the motor asymmetry for cradling infants on the left side) has often been associated to the right-hemispheric social-emotional specialization, and it has often been reported to be stronger in females than in males. In this study we explored the effects of sexual orientation and gender identity on this lateral bias by means of a web-based investigation in a sample of adults (485 biological females and 196 biological males) recruited through LGBTQIA+ networks and general university forums. We exploited a cradling imagery task to assess participants' cradling-side preference, and standardized questionnaires to assess participants' homosexuality (Klein Sexual Orientation Grid) and gender nonconformity (Gender Identity/Gender Dysphoria Questionnaire for Adults and Adolescents). Results confirmed the expected left-cradling bias across all sexual orientation groups except for heterosexual males. Importantly, higher homosexuality scores were associated with higher proportions of left cradling in males. These results suggest that sexual orientation can influence cradling preference in males, indicating a complex interaction between biological and psychological factors in the laterality of social-emotional processing. Finally, the left-cradling bias seems to confirm its role as a behavioral proxy of social-emotional functional lateralization in humans. • Cradling side is a promising proxy of hemispheric specialization in emotions. • Imagined cradling-side preference was assessed in heterosexuals and homosexuals. • Sexual orientation influenced cradling-side preferences in biological males. • Non-heterosexual males' cradling bias was similar to that of heterosexual females. [ABSTRACT FROM AUTHOR]

The Yangtze finless porpoise ( Neophocaena asiaeorientalis asiaeorientalis ) is a critically endangered species with less than 1000 individuals expected to be left in the wild. While many studies have been conducted on laterality among several cetacean species, no studies investigating the Yangtze finless porpoise have been conducted. Using event sampling methods, several behaviors such as flipper-body touching, object touching, barrel-rolls, side swimming, and swimming direction were recorded from six captive porpoises (three males and three females). Analyses of 360 observations recorded over two months revealed that, at group level, porpoises showed laterality in swimming behaviors. Porpoises swam preferentially with their right pectoral fin upward and their left pectoral fin downward with a clockwise swimming direction and also displayed a consistent bias for a counterclockwise barrel-roll direction. No significant differences were reported for flipper use either during the interaction with conspecifics or with objects. The results from the current study provide novel insight into the cerebral asymmetry in a species previously ignored within the literature, thus improving our understanding on the extent of laterality in cetaceans and on the evolutionary history of hemispheric laterality for vertebrates in general. [ABSTRACT FROM AUTHOR]

Twenty-eight captive Sichuan snub-nosed monkeys ( Rhinopithecus roxellana) were involved in the current study. Many individuals showed handedness, with a modest tendency toward left-hand use especially for animate targets, although no group-level handedness was found. There was no significant gender difference in the direction and strength of hand preference for both targets. Females showed a significantly higher overall rate of actions toward animate targets than inanimate targets for both hands, whereas males displayed almost the reversed pattern. There were no significant interactions between lateral hand use and target animacy for either males or females. Most individuals showed rightward or leftward laterality shift trends between inanimate and animate targets. These findings to some extent support the existence of a potential trend concerning a categorical neural distinction between targets demanding functional manipulation (inanimate objects) and those demanding social manipulation (animate objects), even though specialized hand preference based on target animacy has not been fully established in this arboreal Old World monkey species. [ABSTRACT FROM AUTHOR]

This pilot study tested for an association between facial hair whorl characteristics and behavioral responses to a fearful stimulus in horses. Nineteen riding horses were categorized based on hair whorl characteristics (height, lateral location, and rotation). Each horse was subjected to a novel object test where an umbrella was suddenly opened. The turning response was recorded. Hair whorl rotation showed a correlation with turning response with P = .04. Clockwise hair whorls were associated with turning to the right and counterclockwise hair whorls with turning to the left. There were no significant correlations between hair whorl lateral location or height and direction turned ( P > .05). In conclusion, facial hair whorls may be used as a noninvasive method to predict turning response in horses. [ABSTRACT FROM AUTHOR]

The scale-eating cichlid fish, Perissodus microlepis, from Lake Tanganyika are a well-known example of an asymmetry dimorphism because the mouth/head is either left-bending or right-bending. However, how strongly its pronounced morphological laterality is affected by genetic and environmental factors remains unclear. Using quantitative assessments of mouth asymmetry, we investigated its origin by estimating narrow-sense heritability ( h 2) using midparent-offspring regression. The heritability estimates [field estimate: h 2 = 0.22 ± 0.06, P = 0.013; laboratory estimate: h 2 = 0.18 ± 0.05, P = 0.004] suggest that although variation in laterality has some additive genetic component, it is strongly environmentally influenced. Family-level association analyses of a putative microsatellite marker that was claimed to be linked to gene(s) for laterality revealed no association of this locus with laterality. Moreover, the observed phenotype frequencies in offspring from parents of different phenotype combinations were not consistent with a previously suggested single-locus two-allele model, but they neither were able to reject with confidence a random asymmetry model. These results reconcile the disputed mechanisms for this textbook case of mouth asymmetry where both genetic and environmental factors contribute to this remarkable case of morphological asymmetry. [ABSTRACT FROM AUTHOR]

Understanding the relationship between cerebral laterality and intelligence is important in elucidating the neurological underpinnings of individual differences in cognitive abilities. A widely used, behavioral indicator for cerebral laterality, mainly of language, is handedness. A number of studies have compared cognitive abilities between groups of left- and right-handers, while others have investigated the handedness prevalence between groups of different cognitive abilities. The present study comprises five meta-analyses of studies that have assessed the handedness prevalence in (a) individuals with intellectual disability (ID) of unknown/idiopathic nature compared to typically developing (TD) individuals, and (b) individuals with intellectual giftedness (IG) compared to TD individuals. Nineteen data sets totaling 16,076 participants (5795 ID, 8312 TD, and 1969 IG) were included in the analyses. Elevated levels of atypical handedness were found to be robust only for the ID to TD comparison. Findings constrain the range of acceptable theories on the handedness distribution for different intelligence levels. [ABSTRACT FROM AUTHOR]

Background Using senescence-accelerated mouse prone 8 (SAMP8), we examined whether reduced mastication from a young age affects hippocampal-dependent cognitive function. We anesthetized male SAMP8 mice at 8 weeks of age and extracted all maxillary molar teeth of half the animals. The other animals were treated similarly, except that molar teeth were not extracted. At 12 and 24 weeks of age, their general behavior and their ability to recognize novel objects were tested using the open-field test (OFT) and the object-recognition test (ORT), respectively. Results The body weight of molarless mice was reduced significantly compared to that of molarintact mice after the extraction and did not recover to the weight of age-matched molar-intact mice throughout the experimental period. At 12 weeks of age, molarless mice showed significantly greater locomotor activity in the OFT than molar-intact mice. However, the ability of molarless mice to discriminate a novel object in the ORT was impaired compared to that of molar-intact mice. The ability of both molarless and molar-intact SAMP8 mice to recognize objects was impaired at 24 weeks of age. These results suggest that molarless SAMP8 mice develop a deficit of cognitive function earlier than molar-intact SAMP8 mice. Interestingly, both at 12 and 24 weeks of age, molarless mice showed a lateralized preference of object location in the encoding session of the ORT, in which two identical objects were presented. Their lateralized preference of object location was positively correlated with the rightward turning-direction preference, which reached statistical significance at 24 weeks of age. Conclusions Loss of masticatory function in early life causes malnutrition and chronic stress and impairs the ability to recognize novel objects. Hyperactivation and lateralized rotational behavior are commonly observed with dysfunction of the dopaminergic system, therefore, reduced masticatory function may deplete the mesolimbic and mesocorticolimbic dopaminergic systems to impair the cognitive functions of selective attention and recognition memory in the prefrontal cortex and the hippocampus. [ABSTRACT FROM AUTHOR]

The asymmetry in selecting the direction of movement, i.e., the preference to swim clockwise or counterclockwise, was found in yearling roaches Rutilus rutilus (Cyprinidae) placed into a ring-shaped tank under infrared light. A positive correlation was revealed between the behavioral laterality and asymmetry of the surface area of paired frontal bones. Possible causal factors responsible for the correlation between these behavioral and morphological asymmetries are discussed. [ABSTRACT FROM AUTHOR]

The behavior of juvenile 4.5-month-old roach Rutilus rutilus (L.) raised (starting on the 12th day after hatching) at different levels of habitat informational diversity (feeding with live and immobilized zooplankton and benthos, the presence of a predator, and a constant water flow in the nursery aquarium) was studied. The fish's exploratory behavior and locomotor activity were tested in a circular chamber; swimming activity was tested in a hydrodynamic conduit. It was experimentally shown that juvenile roach raised in the presence of a predator differed significantly ( p < 0.05) in regards to behavioral characteristics from the fries raised in a water current and in conditions of a high level of environmental deprivation. [ABSTRACT FROM AUTHOR]

Abstract: Behavioural laterality (e.g., during social interactions) is often observed at the individual level in lower vertebrates such as fish, whereas population-level laterality is observed in many higher vertebrates. Population-level laterality can be explained mainly by internal factors (e.g., cerebral lateralization), whereas little is known about the behavioural mechanisms underlying individual-level laterality. Recently, it was revealed that many fish have asymmetrical body morphology, but the relationship between asymmetric morphology and social behaviours has been rarely examined. Here we report the relationship between lateralized eye use during aggressive displays (e.g., body posture) of male Siamese fighting fish, Betta splendens, toward their own mirror image and morphological asymmetry. Of 25 males, five exhibited significantly more leftward eye use during left displays, and eight males exhibited predominantly rightward eye use during right displays. Morphological measurement results for the craniovertebral angle and opercular area showed that the craniovertebral angle and opercular area displayed antisymmetry and fluctuating asymmetry, respectively. We found that lateralized eye use during agonistic responses by each fish was associated with the craniovertebral angle, but not with operculum size; lefties (left-curved body) showed mainly left eye use (during left-side displays), and righties (right-curved body) demonstrated the opposite. We suggest that antisymmetric morphologies, such as head incline, are potentially useful for studying the association between cerebral lateralization and individual laterality of behavioural responses. Further, we propose that in fish, morphological asymmetry is related to laterality in various behaviours. [Copyright &y& Elsevier]

Background: Anatomic and functional brain lateralization underlies hemisphere specialization for cognitive and motor control, and deviations from the normal patterns of asymmetry appear to be related to behavioral deficits. Studies on n-3 polyunsaturated fatty acid (PUFA) deficiency and behavioral impairments led us to postulate that a chronic lack of n-3 PUFA can lead to changes in lateralized behavior by affecting structural or neurochemical patterns of asymmetry in motor-related brain structures. Methods: We compared the effects of a chronic n-3 PUFA deficient diet with a balanced diet on membrane phospholipid fatty acids composition and immunolabeling of choline acetyltransferase (ChAt), as a marker of cholinergic neurons, in left and right striatum of rats. Lateral motor behavior was assessed by rotation and paw preference. Results: Control rats had an asymmetric PUFA distribution with a right behavioral preference, whereas ChAt density was symmetrical. In deficient rats, the cholinergic neuron density was 30% lower on the right side, associated with a loss of PUFA asymmetry and behavior laterality. They present higher rotation behavior, and significantly more of them failed the handedness test. Conclusion: These results indicate that a lack of n-3 PUFA is linked with a lateral behavior deficit, possibly leading to cognitive disturbances. [Copyright &y& Elsevier]

In a continuously stressful environment, the effects of recurrent prenatal stress (PS) accumulate across generations and generate new behavioral traits in the absence of genetic variation. Here, we investigated if PS or multigenerational PS across 4 generations differentially affect behavioral traits, laterality, and hemispheric dominance in male and female rats. Using skilled reaching and skilled walking tasks, 3 findings support the formation of new behavioral traits and shifted laterality by multigenerational stress. First, while PS in the F1 generation did not alter paw preference, multigenerational stress in the F4 generation shifted paw preference to favor left-handedness only in males. Second, multigenerational stress impaired skilled reaching and skilled walking movement abilities in males, while improving these abilities in females beyond the levels of controls. Third, the shift toward left-handedness in multigenerationally stressed males was accompanied by increased dendritic complexity and greater spine density in the right parietal cortex. Thus, cumulative multigenerational stress generates sexually dimorphic left-handedness and dominance shift toward the right hemisphere in males. These findings explain the origins of apparently heritable behavioral traits and handedness in the absence of DNA sequence variations while proposing epigenetic mechanisms., (© The Author 2016. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.)