Laterality in cats: paw preference and performance in a visuomotor activity

Eye dominance and minor physical anomalies in schizophrenia: relations between two biological markers of abnormal neurodevelopment

Background

To investigate the frequency of left eye dominance and minor physical anomalies (MPAs) in schizophrenia patients and control subjects and determine the interrelations of these two biological markers of neuronal dysontogenesis in schizophrenia.

Subjects and methods

Three tests for eye dominance were administered as performance tasks, not preference questionnaires. Seven MPAs were examined. The sample consisted of 180 (98 schizophrenia patients and 82 control subjects). Several statistical methods for examining the eye tests separately and together were used to assess the difference in left-eyedness between schizophrenia patients and control subjects.

Results

Left eye dominance is significantly higher in schizophrenia subjects. Left-eyed subjects are more stigmatized with MPAs. There is a strong positive correlation between left-eyedness and stigmatization with MPAs in schizophrenia patients.

Conclusion

As hand dominance is under cultural pressure, eye dominance is culturally independent and is useful and reliable indicator of altered hemispheric lateralization. The significant positive correlations between left-eyedness and MPAs and the high concurrence of these biological markers in schizophrenia patients are a potent indicator of underlying aberrant neurodevelopment.

Lessons from behavioral lateralization in olfaction

Sensory information, sampled by sensory organs positioned on each side of the body may play a crucial role in organizing brain lateralization. This question is of particular interest with regard to the growing evidence of alteration in lateralization in several psychiatric conditions. In this context, the olfactory system, an ancient, mostly ipsilateral and well-conserved system across phylogeny may prove an interesting model system to understand the behavioral significance of brain lateralization. Here, we focused on behavioral data in vertebrates and non-vertebrates, suggesting that the two hemispheres of the brain differentially processed olfactory cues to achieve diverse sensory operations, such as detection, discrimination, identification of behavioral valuable cues or learning. These include reports across different species on best performances with one nostril or the other or odorant active sampling by one nostril or the other, depending on odorants or contexts. In some species, hints from peripheral anatomical or functional asymmetry were proposed to explain these asymmetries in behavior. Instigations of brain activation or more rarely of brain connectivity evoked by odorants revealed a complex picture with regards to asymmetric patterns which is discussed with respect to behavioral data. Along the steps of the discussed literature, we propose avenues for future research.

Limb preference and personality in donkeys (Equus asinus)

Interhemispheric laterality has often been linked to different behavioural styles. This study investigates the link between limb preference and personality in donkeys. The sample consisted of 47 donkeys (Equus asinus), 30 males and 17 females. Limb preference was determined using observation of the leading limb in a motionless posture and personality was measured using the Donkey Temperament Questionnaire (French, J. M. (1993). Assessment of donkey temperament and the influence of home environment. Applied Animal Behaviour Science, 36(2), 249-257. doi:10.1016/0168-1591(93)90014-G) completed by the donkeys' keepers. A Principal Component Analysis obtained two components: Agreeableness and Extraversion. Age showed a positive relationship with Agreeableness, echoing trends in humans Donkeys did not show a population-level preference towards either side. Limb preference significantly predicted the trait difficult to handle: donkeys with a preference to keep the right foot forward when motionless were harder to handle. This study presents the first investigation into limb preference and personality in donkeys, although more research is needed to clarify whether there is a population-level limb preference bias in donkeys, and the relationship between limb preference and Agreeableness.

Fighting and mating success in giant Australian cuttlefish is influenced by behavioural lateralization

Behavioural lateralization is widespread. Yet, a fundamental question remains, how can lateralization be evolutionary stable when individuals lateralized in one direction often significantly outnumber individuals lateralized in the opposite direction? A recently developed game theory model predicts that fitness consequences which occur during intraspecific interactions may be driving population-level lateralization as an evolutionary stable strategy. This model predicts that: (i) minority-type individuals exist because they are more likely to adopt unpredictable fighting behaviours during competitive interactions (e.g. fighting); and (ii) majority-type individuals exist because there is a fitness advantage in having their biases synchronized with other conspecifics during interactions that require coordination (e.g. mating). We tested these predictions by investigating biases in giant Australian cuttlefish during fighting and mating interactions. During fighting, most male cuttlefish favoured the left eye and these males showed higher contest escalation; but minority-type individuals with a right-eye bias achieved higher fighting success. During mating interactions, most male cuttlefish favoured the left eye to inspect females. Furthermore, most male cuttlefish approached the female's right side during a mating attempt and these males achieved higher mating success. Our data support the hypothesis that population-level biases are an evolutionary consequence of the fitness advantages involved in intraspecific interactions.

The Alpha Hypothesis: Did Lateralized Cattle-Human Interactions Change the Script for Western Culture?

Domestic cattle possess lateralized cognitive processing of human handlers. This has been recently demonstrated in the preference for large groups of cattle to view a human closely within the predominantly left visual field. By contrast, the same stimulus viewed predominantly within the right visual field promotes a significantly greater frequency of dispersal from a standing position, including flight responses. The respective sets of behaviours correspond with the traditional terms of "near side" for the left side of cattle and horses, and the "off" or "far side" for the right side. These traditional terms of over 300 years usage in the literature communicate functional practicalities for handling livestock and the recognition of lateralized cognitive processing. In this review, the possibility of even earlier recognition and the significance of laterality in cattle-human interaction was argued, from the earliest representations of the letter "A", originally illustrated from nearly 4000 years before the present time as the head of an ox as viewed not from the front or from the right, but from the left (near) side. By extension, this knowledge of lateralization in cattle may represent the earliest written example of applied ethology-the study of the behaviour of animals under human management.

Paw preferences in the Asian small-clawed otter - using an inexpensive, video-based protocol to study laterality of rare species in the zoo

It is still debated whether limb-use preferences represent a common trait in vertebrates, which is based on a shared phylogenetic history. Unravelling the evolutionary origin and pattern of paw preferences in vertebrates requires the analysis of a larger number of species within an ecologically relevant setting. We therefore investigated whether observations in a zoo enable the collection of reliable data sets by quantifying paw use in two independent groups of Asian small-clawed otters (Amblonyx cinerea). Employing a continuous focal animal sampling method, each day one of the ten individuals was video recorded from outside of the enclosure during usual activity. We selected four types of unimanual behaviour (reaching for food, reaching for non-food, reaching into a hole, carrying an object) and quantified paw use for each animal. Our study provides first evidences for individual paw preferences in otters, which were in line with previously reported forelimb use pattern in carnivoran species. Preferences differed between motor acts but for "reaching into a hole" a population-level right paw bias was detected. These data support that observations in a zoological setting are useful to explore task-dependent paw preferences and may facilitate future studies investigating paw preferences under experimentally controlled conditions.

Strategies for obstacle avoidance during walking in the cat

Avoiding obstacles is essential for successful navigation through complex environments. This study aimed to clarify what strategies are used by a typical quadruped, the cat, to avoid obstacles during walking. Four cats walked along a corridor 2.5 m long and 25 or 15 cm wide. Obstacles, small round objects 2.5 cm in diameter and 1 cm in height, were placed on the floor in various locations. Movements of the paw were recorded with a motion capture and analysis system (Visualeyez, PTI). During walking in the wide corridor, cats' preferred strategy for avoiding a single obstacle was circumvention, during which the stride direction changed while stride duration and swing-to-stride duration ratio were preserved. Another strategy, stepping over the obstacle, was used during walking in the narrow corridor, when lateral deviations of walking trajectory were restricted. Stepping over the obstacle involved changes in two consecutive strides. The stride preceding the obstacle was shortened, and swing-to-stride ratio was reduced. The obstacle was negotiated in the next stride of increased height and normal duration and swing-to-stride ratio. During walking on a surface with multiple obstacles, both strategies were used. To avoid contact with the obstacle, cats placed the paw away from the object at a distance roughly equal to the diameter of the paw. During obstacle avoidance cats prefer to alter muscle activities without altering the locomotor rhythm. We hypothesize that a choice of the strategy for obstacle avoidance is determined by minimizing the complexity of neuro-motor processes required to achieve the behavioral goal.NEW & NOTEWORTHY In a study of feline locomotor behavior we found that the preferred strategy to avoid a small obstacle is circumvention. During circumvention, stride direction changes but length and temporal structure are preserved. Another strategy, stepping over the obstacle, is used in narrow walkways. During overstepping, two strides adjust. A stride preceding the obstacle decreases in length and duration. The following stride negotiating the obstacle increases in height while retaining normal temporal structure and nearly normal length.

Can Population-Level Laterality Stem from Social Pressures? Evidence from Cheek Kissing in Humans

Despite extensive research, the origins and functions of behavioural laterality remain largely unclear. One of the most striking unresolved issues is the fact that laterality generally occurs at the population-level. Why would the majority of the individuals of a population exhibit the same laterality, while individual-level laterality would yet provide the advantages in terms of improving behavioural efficiency? Are social pressures the key factor? Can social pressures induce alignment of laterality between the individuals of a population? Can the effect of social pressures overpass the effect of other possible determining factors (e.g. genes)? We tested this important new hypothesis in humans, for the first time. We asked whether population-level laterality could stem from social pressures. Namely, we assessed social pressures on laterality in an interactive social behaviour: kissing on the cheek as a greeting. We performed observations in 10 cities of France. The observations took place in spots where people of the city meet and greet each other. We showed that: a) there is a population-level laterality for cheek kissing, with the majority of individuals being aligned in each city, and b) there is a variation between populations, with a laterality that depends on the city. These results were confirmed by our complementary data from questionnaires and internet surveys. These findings show that social pressures are involved in determining laterality. They demonstrate that population-level laterality can stem from social pressures.

Morphometric description of the feline radius and ulna generated from computed tomography

Objectives

This study aimed to describe the length, internal and external diameters, cancellous bone volume and extent, and cortical thickness at predetermined locations in the radius and ulna of a cohort of skeletally mature, disease-free feline cadavers using radiography and computed tomography (CT).

Methods

Five feline cadavers were used (mean weight 3.31 kg, range 2.55–4.24 kg). Antebrachii (n = 10) were radiographed to confirm skeletal maturity and normal radiographic appearance prior to CT. Reconstructed CT images were used to measure bone length, cortical thickness, internal and external diameters, and cancellous extent. Cancellous bone volume was calculated automatically using OsiriX after manual segmentation (350–850 Hounsfield units window) from axial CT slices.

Results

CT images were used to measure bone length, cortical thickness, internal and external diameters, and cancellous extent and volume. Mean radial length was 95.89 mm (95% confidence interval [CI] 88.52–103.26 mm) and mean ulna length was 114.67 mm (95% CI 105.53–123.81 mm). The olecranon had the largest mean cancellous bone volume (94.16 mm3; 95% CI 72.09–116.23 mm3) and it extended a mean of 13.12 mm (95% CI 11.73–14.51 mm) distally. The radius at the level of the trochlea and the ulna at the level of the coronoid processes had the largest external diameters, respectively. The medullary canal narrowed at the level of the coronoid processes and became cranially eccentric at the proximal third of the diaphysis. The cranial cortex at the level of the coronoid processes and the caudal cortex of the olecranon were markedly thicker than other cortices at those levels.

Conclusions and relevance

Morphometry of the feline antebrachium was described using CT, and should be a useful reference for future research investigations and clinical applications.

Forelimb preferences in quadrupedal marsupials and their implications for laterality evolution in mammals

BACKGROUND

Acquisition of upright posture in evolution has been argued to facilitate manual laterality in primates. Owing to the high variety of postural habits marsupials can serve as a suitable model to test whether the species-typical body posture shapes forelimb preferences in non-primates or this phenomenon emerged only in the course of primate evolution. In the present study we aimed to explore manual laterality in marsupial quadrupeds and compare them with the results in the previously studied bipedal species. Forelimb preferences were assessed in captive grey short-tailed opossum (Monodelphis domestica) and sugar glider (Petaurus breviceps) in four different types of unimanual behaviour per species, which was not artificially evoked. We examined the possible effects of sex, age and task, because these factors have been reported to affect motor laterality in placental mammals.

RESULTS

In both species the direction of forelimb preferences was strongly sex-related. Male grey short-tailed opossums showed right-forelimb preference in most of the observed unimanual behaviours, while male sugar gliders displayed only a slight, not significant rightward tendency. In contrast, females in both species exhibited consistent group-level preference of the left forelimb. We failed to reveal significant differences in manual preferences between tasks of potentially differing complexity: reaching a stable food item and catching live insects, as well as between the body support and food manipulation. No influence of subjects' age on limb preferences was found.

CONCLUSIONS

The direction of sex-related differences in the manual preferences found in quadrupedal marsupials seems to be not typical for placental mammals. We suggest that the alternative way of interhemispheric connection in absence of corpus callosum may result in a fundamentally distinct mechanism of sex effect on limb preferences in marsupials compared to placentals. Our data confirm the idea that non-primate mammals differ from primates in sensitivity to task complexity. Comparison of marsupial species studied to date indicate that the vertical body orientation and the bipedalism favor the expression of individual- and population-level forelimb preferences in marsupials much like it does in primates. Our findings give the first evidence for the effect of species-typical posture on the manual laterality in non-primate mammals.

Right paw foraging bias in wild black bear (Ursus americanus kermodei)

Using field observations of ~15 wild adult black bear (Ursus americanus kermodei) foraging on a salmon stream during two autumns on the central coast of British Columbia, we tested for laterality of forelimb use during lunging and during handling of salmon. Of 288 lunging events observed overall, 53% were non biased, 26% were right-limb biased, and 21% left-limb biased (p = .53 between left and right bias). Among six bears in which we could ascertain individual identity (182 lunging events), there was heterogeneity among individuals (p <.05) of which two were significantly right biased and one significantly left biased (p<.005). Of 186 carcass-handling (pick-up) events, 68% were right-pawed (p <.005) and there was no heterogeneity among five individually identifiable bears (p = .19). There was no forelimb laterality in adjustment of the prey in the mouth or in securing the prey to the substrate. This is the first report of task-specific behavioural lateralisation of a wild carnivore and is suggestive of a right bias (left-hemisphere dominance) in object manipulation.

Cerebral correlates of visual lateralization in Sepia

The common cuttlefish, Sepia officinalis (cephalopod mollusc) has recently become a relevant model for studying the setting-up of brain asymmetry among invertebrates. As the animals age from 3 to 30 days post hatching, they progressively develop a left-turning bias resulting from an eye-use preference. The aim of this study is to investigate whether anatomical (vertical, peduncle, inferior buccal, and optic lobes) or neurochemical (monoamines in optic lobes) brain asymmetries are present in the cuttlefish brain at 3 or at 30 post hatching days; and whether these correlate with side-turning preferences. We here find brain and behavioral asymmetry only at 30 post hatching days. Cuttlefish displayed a significant population bias towards a larger right peduncle lobe, and higher monoamine concentration in the left optic lobe (i.e. serotonin, dopamine and noradrenaline). None of these brain asymmetries were correlated to the studied side-turning bias. However, we found individual variation in the magnitude of the vertical and optic lobes asymmetry. A striking correlation was found with the behavioral results: the larger the right optic lobe and the right part of the vertical lobe, the stronger the bias to turn leftwards. To our knowledge, this is the first study to demonstrate a relationship at the individual level between brain and behavioral asymmetries in invertebrates.

Jaw laterality and related handedness in the hunting behavior of a scale-eating characin, Exodon paradoxus

BACKGROUND

Asymmetry in animal bodies and behavior has evolved several times, but our knowledge of their linkage is limited. Tanganyikan scale-eating cichlids have well-known antisymmetry in their bodies and behavior; individuals open their mouths leftward (righty) or rightward (lefty), and righties always attack the right flank of the prey, whereas lefties attack the left. This study analyzed the morphological asymmetry in a scale-eating characiform, Exodon paradoxus, and its behavioral handedness.

METHODOLOGY/PRINCIPAL FINDINGS

Each eight E. paradoxus was observed for 1-h with a prey goldfish in an aquarium to detect the behavioral handedness. Following the experiment, the lateral differences in the mandibles and head-inclination of these eight and ten additional specimens were analyzed. Both measurements on the morphology showed a bimodal distribution, and the laterality identified by these two methods was always consistent within a given individual, indicating that the characin has morphological antisymmetry. Furthermore, this laterality significantly corresponded to behavioral handedness; that is, lefties more often rasped scales from the right flank of the prey and vice versa. However, the correlation between laterality and handedness is the opposite of that in the cichlids. This is due to differences in the feeding apparatus and technique. The characin has cuspids pointing forward on the external side of the premaxilla, and it thrusts its dominant body side outward from its body axis on the flank of the prey to tear off scales. By contrast, the cichlids draw their dominant body side inward toward the axis or rotate it to scrape or wrench off scales with the teeth lined in the opened mouth.

CONCLUSIONS/SIGNIFICANCE

This study demonstrated that the antisymmetry in external morphology and the corresponding behavioral handedness have evolved in two lineages of scale-eating fishes independently, and these fishes adopt different utilization of their body asymmetry to tear off scales.

Lateralized behaviour of a non-social cichlid fish (Amatitlania nigrofasciata) in a social and a non-social environment

Cerebral lateralization, the partitioning of cognitive function preferentially into one hemisphere of the brain, is a trait ubiquitous among vertebrates. Some species exhibit population level lateralization, where the pattern of cerebral lateralization is the same for most members of that species; however, other species show only individual level lateralization, where each member of the species has a unique pattern of lateralized brain function. The pattern of cerebral lateralization within a population and an individual has been shown to differ based on the stimulus being processed. It has been hypothesized that sociality within a species, such as shoaling behaviour in fish, may have led to the development and persistence of population level lateralization. Here we assessed cerebral lateralization in convict cichlids (Amatitlania nigrofasciata), a species that does not shoal as adults but that shoals briefly as juveniles. We show that both male and female convict cichlids display population level lateralization when in a solitary environment but only females show population level lateralization when in a perceived social environment. We also show that the pattern of lateralization differs between these two tasks and that strength of lateralization in one task is not predictive of strength of lateralization in the other task.

Reciprocal organization of the cerebral hemispheres

The cerebral hemispheres are anatomically and neurophysiologically asymmetrical. The evolutionary basis for these differences remains uncertain. There are, however, highly consistent differences between the hemispheres, evident in reptiles, birds, and mammals, as well as in humans, in the nature of the attention each applies to the environment. This permits the simultaneous application of precisely focused, but narrow, attention, needed for grasping food or prey, with broad, open, and uncommitted attention, needed to watch out for predators and to interpret the intentions of conspecifics. These different modes of attention can account for a very wide range of repeated observations relating to hemisphere specialization, and suggest that hemisphere differences lie not in discrete functional domains as such, but distinct modes of functioning within any one domain. These modes of attention are mutually incompatible, and their application depends on inhibitory transmission in the corpus callosum. There is also an asymmetry of interaction between the hemispheres at the phenomenological level.

Illness as a source of variation of laterality in lions (Panthera leo)

Brain asymmetry--i.e. the specialisation of each cerebral hemisphere for sensorimotor processing mechanisms and for specific cognitive functions-is widely distributed among vertebrates. Several factors, such as embryological manipulations, sex, age, and breeds, can influence the maintenance, strength, and direction of laterality within a certain vertebrate species. Brain lateralisation is a universal phenomenon characterising not only cerebral control of cognitive or emotion-related functions but also cerebral regulation of somatic processes, and its evolution is strongly influenced by social selection pressure. Diseases are well known to be a cost of sociality but their role in influencing behaviour has received very little attention. The present study investigates the influence of illness conditions as a source of variation on laterality in a social keystone vertebrate predator model, the lion. In a preliminary stage, the clinical conditions of 24 adult lions were assessed. The same animals were scored for forelimb preference when in the quadrupedal standing position. Lions show a marked forelimb preference with a population bias towards the use of the right forelimb. Illness conditions strongly influenced the strength of laterality bias, with a significant difference between clinically healthy and sick lions. According to these results, health conditions should be recognised as an important source of variation in brain lateralisation.

Intraspecific competition and coordination in the evolution of lateralization

Recent studies have revealed a variety of left-right asymmetries among vertebrates and invertebrates. In many species, left- and right-lateralized individuals coexist, but in unequal numbers ('population-level' lateralization). It has been argued that brain lateralization increases individual efficiency (e.g. avoiding unnecessary duplication of neural circuitry and reducing interference between functions), thus counteracting the ecological disadvantages of lateral biases in behaviour (making individual behaviour more predictable to other organisms). However, individual efficiency does not require a definite proportion of left- and right-lateralized individuals. Thus, such arguments do not explain population-level lateralization. We have previously shown that, in the context of prey-predator interactions, population-level lateralization can arise as an evolutionarily stable strategy when individually asymmetrical organisms must coordinate their behaviour with that of other asymmetrical organisms. Here, we extend our model showing that populations consisting of left- and right-lateralized individuals in unequal numbers can be evolutionarily stable, based solely on strategic factors arising from the balance between antagonistic (competitive) and synergistic (cooperative) interactions.

Increased Frequency of Left-Handedness in Patients with Unilateral Coronal Synostosis

Objective:

Left-handedness reportedly has been more common in persons with neurological afflictions (e.g., stroke) and malformations (e.g., cleft lip with or without cleft palate) that demonstrate marked unilateral involvement. Coronal synostosis is also more frequently unilateral, affecting the right side more commonly than the left. We sought to compare left-handedness in patients with unilateral coronal synostosis versus healthy controls.

Subjects:

All patients aged 3 years or older with nonsyndromic unilateral coronal synostosis and healthy controls recruited by pediatricians blinded to the study.

Main Outcome Measures:

Prospective data obtained for all participants included age, gender, and handedness. In patients with unilateral coronal synostosis, the side of synostosis and age at surgery were documented. Left-handedness in the study and control groups was compared using chi-square analysis. Left-handedness also was analyzed in the study group according to side of fusion.

Results:

Eighty-six patients with nonsyndromic unilateral coronal synostosis comprised the study group; there were 96 controls. The mean ages of the study (8.8 years) and control groups (9.8 years) were not statistically different (p > .05). There were more girls in the study group (67%) than in the control group (56%), but this difference was not statistically significant (p > .05). Left-handedness was documented in 30.2% of the study group and 11.4% of the control group (p < .005). Left-handedness was twice as common in patients with left versus right unilateral coronal synostosis (44.4% versus 20.4%; p < .05).

Conclusions:

Left-handedness is nearly three times more common in patients with unilateral coronal synostosis than in controls and four times more likely in patients with left-sided fusion.

Hand and paw preferences in relation to the lateralized brain

Hand preferences of primates are discussed as part of the broad perspective of brain lateralization in animals, and compared with paw preferences in non-primates. Previously, it has been suggested that primates are more likely to express a species-typical hand preference on complex tasks, especially in the case of coordinated hand use in using tools. I suggest that population-level hand preferences are manifested when the task demands the obligate use of the processing specialization of one hemisphere, and that this depends on the nature of the task rather than its complexity per se. Depending on the species, simple reaching tasks may not demand the obligate use of a specialized hemisphere and so do not constrain limb/hand use. In such cases, individuals may show hand preferences that are associated with consistent differences in behaviour. The individual's hand preference is associated with the expression of behaviour controlled by the hemisphere contralateral to the preferred hand (fear and reactivity in left-handed individuals versus proactivity in right-handed individuals). Recent findings of differences in brain structure between left- and right-handed primates (e.g. somatosensory cortex in marmosets) have been discussed and related to potential evolutionary advances.

Molecular approaches to brain asymmetry and handedness

In the human brain, distinct functions tend to be localized in the left or right hemispheres, with language ability usually localized predominantly in the left and spatial recognition in the right. Furthermore, humans are perhaps the only mammals who have preferential handedness, with more than 90% of the population more skillful at using the right hand, which is controlled by the left hemisphere. How is a distinct function consistently localized in one side of the human brain? Because of the convergence of molecular and neurological analysis, we are beginning to consider the puzzle of brain asymmetry and handedness at a molecular level.

Dog paw preference shows lability and sex differences

Paw preferences in domestic dogs were studied using three different behavioural tests, recording frequency, duration and latency of paw use. No overall population tendency to right- or left-paw preference was seen on any of the tests, nor could a sub-population of handed dogs be detected. This failure to replicate previous reports that male dogs tend to use their left paws while females use their right was counterbalanced by a significant tendency for male dogs to use their left paw when initially presented with one test, and for the latency of left paw use to be significantly shorter than that for right paw use on these initial presentations. This significant effect disappeared with repeated presentation of the test, and was not present in females. We conclude that behavioural lateralisation appears to be a labile category in dogs, and may be related to brain hemispheric effects in responding to novel stimuli.

Blood brain barrier in right- and left-pawed female rats assessed by a new staining method

The asymmetrical breakdown of the blood-brain barrier (BBB) was studied in female rats. Paw preference was assessed by a food reaching test. Adrenaline-induced hypertension was used to destroy the BBB, which was evaluated using triphenyltetrazolium (TTC) staining of the brain slices just after giving adrenaline for 30 s. In normal rats, the whole brain sections exhibited complete staining with TTC. After adrenaline infusion for 30 s, there were large unstained areas in the left brain in right-pawed animals, and vice versa in left-pawed animals. Similar results were obtained in seizure-induced breakdown of BBB. These results were explained by an asymmetric cerebral blood flow depending upon the paw preference in rats. It was suggested that this new method and the results are consistent with contralateral motor control that may be important in determining the dominant cerebral hemisphere in animals.

Leading-limb preferences in marmosets (Callithrix jacchus): Walking, leaping and landing

The leading-limb preferences of 17 common marmosets (Callithrix jacchus) when they initiated and terminated locomotion were determined from video recordings of the subjects walking on, leaping off, and landing on a plexiglas platform. In a majority of sequences, 11 of 17 subjects landed with the right hand and foot contacting the plexiglas substrate before the left hand and foot. Of the 17 subjects, 8 initiated leaping with the right side of the body, whereas only 3 subjects significantly preferred to initiate leaping with the left hand and foot. Leading-limb preferences displayed during landing were positively correlated with those displayed for leaping and walking, although only two subjects displayed significant leading-limb preferences when walking. By contrast, hand preferences for initiating and terminating locomotion were not related to hand preferences for food holding; 16 of 17 marmosets displayed strong and significant hand preferences for food holding, even though many did not show leading-limb preferences for walking, leaping, or landing. These data seem to suggest that the right arm is stronger in marmosets. The right arm is used initially to decelerate the body and absorb the impact of contact with the landing substrate. The tendency for the right arm to be stronger is balanced by a tendency for the left leg to be stronger (providing the force needed for leaping).

Lateralization of response to social stimuli in fishes: a comparison between different methods and species

We measured the time spent in monocular viewing during inspection of their own mirror images in females of three species of fish (Xenotoca eiseni, Gambusia holbrooki and Xenopoecilus sarasinorum) using a rectangular tank in which animals could observe their own reflections in two mirrors positioned along the major walls, and in females of five species of fish (X. eiseni, G. holbrooki, X. sarasinorum, Danio rerio and Gnatonemus petersii) using a quasi-circular tank in which fish could rotate clockwise or anticlockwise and observe their own reflections in a mirror positioned along the outer wall. Results revealed a consistent left-eye preference during initial sustained fixation in all species irrespective of the apparatus. However, in the quasi-circular tank, fish showed more variability of response. The asymmetry was apparent during the first 5 min of observation and tended to fade thereafter, probably as a result of habituation. These findings add to current evidence for a quite invariant pattern in the direction of lateralization in similar tasks in a variety of vertebrate species, with a preferential involvement of structures located to the right side of the brain in response to the viewing of images of conspecifics.

Evolution of hemispheric specialization: advantages and disadvantages

Lateralization of the brain appeared early in evolution and many of its features appear to have been retained, possibly even in humans. We now have a considerable amount of information on the different forms of lateralization in a number of species, and the commonalities of these are discussed, but there has been relatively little investigation of the advantages of being lateralized. This article reports new findings on the differences between lateralized and nonlateralized chicks. The lateralized chicks were exposed to light for 24 h on day 19 of incubation, a treatment known to lead to lateralization of a number of visually guided responses, and the nonlateralized chicks were incubated in the dark. When they were feeding, the lateralized chicks were found to detect a stimulus resembling a raptor with shorter latency than nonlateralized chicks. This difference was not a nonspecific effect caused by the light-exposed chicks being more distressed by the stimulus. Instead, it appears to be a genuine advantage conferred by having a lateralized brain. It is suggested that having a lateralized brain allows dual attention to the tasks of feeding (right eye and left hemisphere) and vigilance for predators (left eye and right hemisphere). Nonlateralized chicks appear to perform these dual tasks less efficiently than lateralized ones. Reference is made to other species in discussing these results.

Do monkeys choose the more skillful hand in manual problem-solving?

To investigate the relationship between manual skills and hand preference in 4 female Japanese monkeys (Macaca fuscata), the technique of concurrent investigation of manual skills and hand preference was introduced. 4 female Japanese monkeys were required to take food out of a pipe using the left hand and right hand alternately. The performance time and the number of deviations from alternate sequence were recorded as measure of manual skills and hand preference. In the result, the preferred hand was not always consistently the skillful one; however, only one subject tended to choose the more skillful hand in problem-solving, and another subject learned the alternate sequence of reaching. The performances of two subjects indicated discrimination of both hands in Japanese monkeys is possible.

Lexicon size and its relation to foot preference in the African grey parrot (Psittacus erithacus)

To study footedness in parrots, an international survey of parrot owners was conducted. Responses were obtained from 524 individuals, including 70 owners of African Grey parrots (all animals > or = 10 months old). All respondents were given a 10-item questionnaire and a standard method for testing foot preference in their pets, and they were asked to count the number of separate words in their pets' lexicons of human speech sounds. Right-footed African Greys (N = 36) had significantly larger lexicons than left-footed African Greys (N = 34; P = 0.01). This difference could not be accounted for by group differences in training efforts or socialization/housing with conspecifics. A non-significant trend in the same direction was found in a comparison sample of Amazon parrots, although these genera are less adept than African Greys at learning human speech sounds. Other investigators have provided convincing evidence of lateralization, in the avian brain, for the analysis and memory of differing types of stimuli. In addition, there appears to be preferential left hypserstriatal activation for long-term memory consolidation. Our results suggest a relationship between lateral asymmetry for motor preference and asymmetric CNS mediation of a 'higher cognitive' function (i.e. the categorization and long-term mnestic processing of human speech sound.

Patterns of lateral preference in psychotic patients

Two tests of lateral preference (hand-clasping and arm-folding) were investigated in 50 adult right-handed healthy controls and in 42 right-handed psychotic patients. In the psychotics, hand-clasping and arm-folding with uppermost left positions were less evident than in the controls. In the psychotics with uppermost right positions in both tests (including handedness, i.e. unilateral right), good prognostic clinical features were most pronounced. These results, which were predominantly found in the males, are interpreted on the basis of possible relationships between hemispheric asymmetries and lateral preferences.

Structure, functional and cerebral asymmetry: in vivo morphometry of the planum temporale

Using high-resolution magnetic resonance (MR) imaging, the normal left-right asymmetry of the planum temporale (PT) can be quantified accurately and reliably in the intact human brain. The following main results have emerged from MR measurements of individual direction and degree of PT asymmetry. (1) Normal left-handers are less left-lateralized than normal right-handers, without significant gender effects. This confirms a structural-functional correlation in cerebral asymmetry. (2) The aforementioned handedness difference in PT asymmetry is also found in pairs of normal monozygotic twins discordant for handedness. Thus, structural brain asymmetry may not be genetically determined. (3) Whereas right-handed patients with developmental deficits of phonological processing have been reported to show decrease PT asymmetry, musicians with perfect pitch display exaggerated leftward asymmetry. Thus, increasing leftward asymmetry of auditory-related cortices covering the PT may be correlated with the processing capacity for certain auditory features. Studies of the PT as a structural marker of cerebral asymmetry will continue to contribute to a better understanding of the phylogeny and ontogeny of laterality.