The evolution and genetics of cerebral asymmetry

The Association Between Grip Strength, Upper Body Power, and Limb Dominance in a Military Population

INTRODUCTION

Military service members rely on upper body strength and power to accomplish tasks such as carrying heavy weapons and gear, rappelling, combat grappling, and marksmanship. Early identification of the factors that lead to reduced upper body strength and power would enable leadership to predict and mitigate aspects that decrease military operational readiness and increase injury risk. The purpose of this study was to investigate the relationship between grip strength and upper body power in U.S. Infantry Marines. We hypothesized that dominant arm grip strength would show a strong positive correlation with upper body power and that the dominant arm would be more powerful than the non-dominant arm.

MATERIALS AND METHODS

A total of 120 U.S. Marines completed 3 maximum effort isometric grip strength trials with their dominant hand and 3 maximum effort ballistic pushups on a ForceDecks force plate system. Force plate data were used to estimate pushup height and peak power. Maximum grip strength, pushup height, and peak power across the 3 trials were used for analysis. Pearson's correlation was used to test for associations between peak power, pushup height, and grip strength. Paired t-tests were used to test for differences in peak power between the dominant and non-dominant arms.

RESULTS

A very weak correlation was found between grip strength and upper body power, but there was no relationship between grip strength and pushup height. Additionally, there were no significant differences in upper body power between the dominant and non-dominant arms.

CONCLUSIONS

The results of this study suggest that grip strength is not predictive of upper body power and cannot be used as a stand-alone measure of physical readiness in a military unit. These findings do not, however, degrade the potential of both measures to predict and inform health status and physical readiness. Future prospective research should be conducted to determine if either of these measures can be used as indicators of performance and/or injury susceptibility and if limb dominance plays a role in injury incidence within the upper extremity.

Altered asymmetry of functional connectome gradients in major depressive disorder

Introduction

Major depressive disorder (MDD) is a debilitating disease involving sensory and higher-order cognitive dysfunction. Previous work has shown altered asymmetry in MDD, including abnormal lateralized activation and disrupted hemispheric connectivity. However, it remains unclear whether and how MDD affects functional asymmetries in the context of intrinsic hierarchical organization.

Methods

Here, we evaluate intra- and inter-hemispheric asymmetries of the first three functional gradients, characterizing unimodal-transmodal, visual-somatosensory, and somatomotor/default mode-multiple demand hierarchies, to study MDD-related alterations in overarching system-level architecture.

Results

We find that, relative to the healthy controls, MDD patients exhibit alterations in both primary sensory regions (e.g., visual areas) and transmodal association regions (e.g., default mode areas). We further find these abnormalities are woven in heterogeneous alterations along multiple functional gradients, associated with cognitive terms involving mind, memory, and visual processing. Moreover, through an elastic net model, we observe that both intra- and inter-asymmetric features are predictive of depressive traits measured by BDI-II scores.

Discussion

Altogether, these findings highlight a broad and mixed effect of MDD on functional gradient asymmetry, contributing to a richer understanding of the neurobiological underpinnings in MDD.

The Relationship Between the Motor Lateralization and the Concentration of Cortisol and Tyrosine in Dogs Exposed to Stress During Veterinary Activities

The aim of the study was to assess the relationship between the motor lateralization in dogs and the concentration of cortisol and tyrosine in their plasma during a visit to a veterinary clinic. The research group consisted of 56 dogs. Motor lateralization was tested by of an adhesive tape test. The stress intensity was assessed basing on the levels of cortisol and ft4 in the serum blood. The statistical analysis revealed that in the group of 56 dogs there were 14 left-pawed dogs, 36 right-pawed dogs, and 6 dogs did not show particular paw preference. The average cortisol levels in particular groups were as follows: 7.94 ug/dl, 3.92 ug/dl and 3.7 ug/dl, whereas the level of tyrosine in the subjects that demonstrated left-sided lateralization (mean ± SE) (1.95 ± 0.46 ng/dl) for those with right-side lateralization (1.56 ± 0.23 ng/dl) and ambilateral dogs (1.01 ± 0.22 ng/dl). The statistical calculation of Pearson's χ2 showed a significant relationship between the sex and the lateralization (χ2 = 6.238, df = 2, p = 0.0442).

Using rare genetic mutations to revisit structural brain asymmetry

Asymmetry between the left and right hemisphere is a key feature of brain organization. Hemispheric functional specialization underlies some of the most advanced human-defining cognitive operations, such as articulated language, perspective taking, or rapid detection of facial cues. Yet, genetic investigations into brain asymmetry have mostly relied on common variants, which typically exert small effects on brain-related phenotypes. Here, we leverage rare genomic deletions and duplications to study how genetic alterations reverberate in human brain and behavior. We designed a pattern-learning approach to dissect the impact of eight high-effect-size copy number variations (CNVs) on brain asymmetry in a multi-site cohort of 552 CNV carriers and 290 non-carriers. Isolated multivariate brain asymmetry patterns spotlighted regions typically thought to subserve lateralized functions, including language, hearing, as well as visual, face and word recognition. Planum temporale asymmetry emerged as especially susceptible to deletions and duplications of specific gene sets. Targeted analysis of common variants through genome-wide association study (GWAS) consolidated partly diverging genetic influences on the right versus left planum temporale structure. In conclusion, our gene-brain-behavior data fusion highlights the consequences of genetically controlled brain lateralization on uniquely human cognitive capacities.

Handedness in autism spectrum disorders and intellectually disabled children and adolescents - Contrasting caregivers' reports with assessments of hand preference

Background

A higher rate of atypical handedness prevalence (non-right-handedness or left-, mixed-hand dominance) has been recurrently reported in individuals diagnosed with autism spectrum disorder (ASD) compared to individuals with other types of developmental disabilities. However, the exact magnitude of this difference as well as the presence of possible contributing factors remained unknown. The main aim of this study was to understand caregivers' impression of the handedness of their child with developmental disabilities and its relationship with assessments of the child using a hand preference scale.

Methods and procedures

The sample of the present study was 1116 individuals with developmental disabilities from two countries, 541 (51.5%) individuals from Iran and 575 (48.5%) individuals from the Kurdistan Region of Iraq (KRI). The handedness of the sample was evaluated based on the parental report and utilizing a standardized scale (The Hand-Preference Demonstration Test "HPDT").

Outcomes and results

There was a statistically significant difference between caregivers' reports on their dependents' handedness and the application of a valid hand preference scale and they do not necessarily overlap. There was a statistically significant relationship between handedness and type of developmental disabilities based on caregivers' reports and individuals with ASD were more non-right-handed compared to individuals with ID based on the caregivers' report. Hence similar difference was not seen between the ASD and ID groups when HDTP was applied as a diagnostic scale. While left-handedness in the ASD and ID group was similar (23-24%), mixed-handedness in the ASD group was 38% compared to 33% in the ID group.

Conclusions and implications

The Hand-Preference Demonstration Test (HPDT) was a valid way to determine the hand preference of individuals with ASD and ID. It is concluded that parental reports on their offspring with ASD's hand preference need to be approved through the application of a scale and caregivers and professionals need to be more aware of early motor symptoms such as handedness. Further research should focus on the role of handedness in the development of fine motor skills and eye-hand coordination in children with differing developmental disabilities and variations among those differing impairments.

Fingerprint patterns in relation to an altered neurodevelopment in patients with autism spectrum disorder

Dermatoglyphic patterns are permanently established and matured before the 24th week of gestation. Their frequencies and localization might be a good indicator of developmental instability in individuals with an altered neurodevelopment and show potential as biomarkers of autism spectrum disorder (ASD). In this study, fingerprint pattern counts and fluctuating asymmetry in the distribution of patterns are compared between 67 boys diagnosed with ASD (aged 5.11 ± 2.51 years) and 83 control boys (aged 8.58 ± 3.14 years). Boys with ASD had a higher rate of discordance in their fingerprint patterns (p = .0026), showing more often bilateral differences in the occurrence of certain patterns. A chi-square test revealed that the difference in pattern frequencies between boys with ASD and the control group is the most significant in frequencies of whorls, tented arches, and ulnar loops. Boys with ASD have significantly fewer ulnar loops, significantly more whorls, and tented arches in the right hand. The achieved results are in favor of the suggestion that prenatal influences, which play a role in the development of bilateral differences in fingerprint patterns up to the 24th week of gestation, may be a potential cause of an altered neurodevelopment in ASD individuals.

Evidence for a left ear bias in incidence of Meniere's disease

OBJECTIVE

To explore a side of lesion differences in Meniere's disease (MD).

DESIGN

A retrospective review (2019-2021) was conducted of patients with definite MD, as defined by 2015 Bárány Society diagnostic criteria. Testing information included pure tone audiometry, tympanometry, and extra-tympanic electrocochleography (ECochG). Normative ECochG data from healthy subjects determined the 95% cut-off value for clinical abnormality.

STUDY SAMPLE

107 patients with definite MD were included in the study and 40 healthy controls.

RESULTS

The review identified 75 patients with unilateral MD and 32 patients with bilateral MD according to their clinical histories. 79% of unilateral cases were found to have MD on the L ear. 94% of bilateral MD cases had L ears more affected than R ears. Objective ECochG testing indicated a greater incidence of elevated SP/AP area curve and amplitude ratios in L ears. On binomial testing, all results indicate a highly significant bias of MD to the L side.

CONCLUSIONS

Unilateral MD appears more common on the L side than the R, suggesting that the disease process underlying MD is not symmetrical. MD also appears more common in females than males. It appears that there is a physiological asymmetry in the progression/cause of MD.

Modulation of rhythmic visual stimulation on left-right attentional asymmetry

The rhythmic visual stimulation (RVS)-induced oscillatory brain responses, namely steady-state visual evoked potentials (SSVEPs), have been widely used as a biomarker in studies of neural processing based on the assumption that they would not affect cognition. However, recent studies have suggested that the generation of SSVEPs might be attributed to neural entrainment and thus could impact brain functions. But their neural and behavioral effects are yet to be explored. No study has reported the SSVEP influence on functional cerebral asymmetry (FCA). We propose a novel lateralized visual discrimination paradigm to test the SSVEP effects on visuospatial selective attention by FCA analyses. Thirty-eight participants covertly shifted their attention to a target triangle appearing in either the lower-left or -right visual field (LVF or RVF), and judged its orientation. Meanwhile, participants were exposed to a series of task-independent RVSs at different frequencies, including 0 (no RVS), 10, 15, and 40-Hz. As a result, it showed that target discrimination accuracy and reaction time (RT) varied significantly across RVS frequency. Furthermore, attentional asymmetries differed for the 40-Hz condition relative to the 10-Hz condition as indexed by enhanced RT bias to the right visual field, and larger Pd EEG component for attentional suppression. Our results demonstrated that RVSs had frequency-specific effects on left-right attentional asymmetries in both behavior and neural activities. These findings provided new insights into the functional role of SSVEP on FCAs.

Taking Sides: Asymmetries in the Evolution of Human Brain Development in Better Understanding Autism Spectrum Disorder

Confirmation from structural, functional, and behavioral studies agree and suggest a configuration of atypical lateralization in individuals with autistic spectrum disorders (ASD). It is suggested that patterns of cortical and behavioral atypicality are evident in individuals with ASDs with atypical lateralization being common in individuals with ASDs. The paper endeavors to better understand the relationship between alterations in typical cortical asymmetries and functional lateralization in ASD in evolutionary terms. We have proposed that both early genetic and/or environmental influences can alter the developmental process of cortical lateralization. There invariably is a “chicken or egg” issue that arises whether atypical cortical anatomy associated with abnormal function, or alternatively whether functional atypicality generates abnormal structure.

Greater volumes of a callosal sub-region terminating in posterior language-related areas predict a stronger degree of language lateralization: A tractography study

Language lateralization is the most intriguing trait of functional asymmetry for cognitive functions. Nowadays, ontogenetic determinants of this trait are largely unknown, but there are efforts to find its anatomical correlates. In particular, a white matter interhemispheric connection-the corpus callosum-has been proposed as such. In the present study, we aimed to find the association between the degree of language lateralization and metrics of the callosal sub-regions. We applied a sentence completion fMRI task to measure the degree of language lateralization in a group of healthy participants balanced for handedness. We obtained the volumes and microstructural properties of callosal sub-regions with two tractography techniques, diffusion tensor imaging (DTI) and constrained spherical deconvolution (CSD). The analysis of DTI-based metrics did not reveal any significant associations with language lateralization. In contrast, CSD-based analysis revealed that the volumes of a callosal sub-region terminating in the core posterior language-related areas predict a stronger degree of language lateralization. This finding supports the specific inhibitory model implemented through the callosal fibers projecting into the core posterior language-related areas in the degree of language lateralization, with no relevant contribution of other callosal sub-regions.

Hemispheric asymmetries for emotions in non-human primates: A systematic review

A systematic review of investigations evaluating hemispheric asymmetries for emotions in primates was undertaken to individuate the most consistent lines of research allowing to check the hypothesis of a continuum in emotional lateralization across vertebrates. We reviewed studies on the lateralization of emotional expression (N = 31) and perception (N = 32) and of markers of emotional activation (N = 9), trying to distinguish those which had given respectively more consistent or more conflicting outcomes. Furthermore, we tried to identify the most strongly supported model of emotional lateralization. The most consistent results were obtained in studies investigating asymmetries in emotional expression at the facial level and in the perception of emotional facial expressions, whereas the most disappointing data were obtained in investigations evaluating possible neurophysiological markers of lateralized emotional activation. These results supported more the hypothesis of a continuity between humans and non-human primates than the more general hypothesis of a continuum between humans and all vertebrates. Furthermore, results supported more the 'right hemisphere' than the 'valence' model of emotional lateralization.

Heritability and cross-species comparisons of human cortical functional organization asymmetry

The human cerebral cortex is symmetrically organized along large-scale axes but also presents inter-hemispheric differences in structure and function. The quantified contralateral homologous difference, that is asymmetry, is a key feature of the human brain left-right axis supporting functional processes, such as language. Here, we assessed whether the asymmetry of cortical functional organization is heritable and phylogenetically conserved between humans and macaques. Our findings indicate asymmetric organization along an axis describing a functional trajectory from perceptual/action to abstract cognition. Whereas language network showed leftward asymmetric organization, frontoparietal network showed rightward asymmetric organization in humans. These asymmetries were heritable in humans and showed a similar spatial distribution with macaques, in the case of intra-hemispheric asymmetry of functional hierarchy. This suggests (phylo)genetic conservation. However, both language and frontoparietal networks showed a qualitatively larger asymmetry in humans relative to macaques. Overall, our findings suggest a genetic basis for asymmetry in intrinsic functional organization, linked to higher order cognitive functions uniquely developed in humans.

A Weak Shadow of Early Life Language Processing Persists in the Right Hemisphere of the Mature Brain

Studies of language organization show a striking change in cerebral dominance for language over development: We begin life with a left hemisphere (LH) bias for language processing, which is weaker than that in adults and which can be overcome if there is a LH injury. Over development this LH bias becomes stronger and can no longer be reversed. Prior work has shown that this change results from a significant reduction in the magnitude of language activation in right hemisphere (RH) regions in adults compared to children. Here we investigate whether the spatial distribution of language activation, albeit weaker in magnitude, still persists in homotopic RH regions of the mature brain. Children aged 4-13 (n = 39) and young adults (n = 14) completed an auditory sentence comprehension fMRI (functional magnetic resonance imaging) task. To equate neural activity across the hemispheres, we applied fixed cutoffs for the number of active voxels that would be included in each hemisphere for each participant. To evaluate homotopicity, we generated left-right flipped versions of each activation map, calculated spatial overlap between the LH and RH activity in frontal and temporal regions, and tested for mean differences in the spatial overlap values between the age groups. We found that, in children as well as in adults, there was indeed a spatially intact shadow of language activity in the right frontal and temporal regions homotopic to the LH language regions. After a LH stroke in adulthood, recovering early-life activation in these regions might assist in enhancing recovery of language abilities.

From Hemispheric Asymmetry through Sensorimotor Experiences to Cognitive Outcomes in Children with Cerebral Palsy

Recent neuroimaging studies allowed us to explore abnormal brain structures and interhemispheric connectivity in children with cerebral palsy (CP). Behavioral researchers have long reported that children with CP exhibit suboptimal performance in different cognitive domains (e.g., receptive and expressive language skills, reading, mental imagery, spatial processing, subitizing, math, and executive functions). However, there has been very limited cross-domain research involving these two areas of scientific inquiry. To stimulate such research, this perspective paper proposes some possible neurological mechanisms involved in the cognitive delays and impairments in children with CP. Additionally, the paper examines the ways motor and sensorimotor experience during the development of these neural substrates could enable more optimal development for children with CP. Understanding these developmental mechanisms could guide more effective interventions to promote the development of both sensorimotor and cognitive skills in children with CP.

Behavioral and Evolutionary Perspectives on Visual Lateralization in Mating Birds: A Short Systematic Review

The division of cognitive processing between the two hemispheres of the brain causes lateralized eye use in various behavioral contexts. Generally, visual lateralization is shared among vertebrates to a greater extent, with little interspecific variation. However, previous studies on the visual lateralization in mating birds have shown surprising heterogeneity. Therefore, this systematic review paper summarized and analyzed them using phylogenetic comparative methods. The review aimed to elucidate why some species used their left eye and others their right to fixate on individuals of the opposite sex, such as mating partners or prospective mates. It was found that passerine and non-passerine species showed opposite eye use for mating, which could have stemmed from the difference in altricial vs. precocial development. However, due to the limited availability of species data, it was impossible to determine whether the passerine group or altricial development was the primary factor. Additionally, unclear visual lateralization was found when studies looked at lek mating species and males who performed courtship. These findings are discussed from both evolutionary and behavioral perspectives. Possible directions for future research have been suggested.

Modulation of Auditory Perception Laterality under Anxiety and Depression Conditions

The objective of this work is to confirm the asymmetry in non-linguistic auditory perception, as well as the influence of anxiety-depressive disorders on it. Eighty-six people were recruited in the emotional well-being group, fifty-six in the anxiety group, fourteen in the depression group, and seventy-seven in the mixed group. In each group, audiograms were obtained from both ears and the differences were statistically analyzed. Differences in hearing sensitivity were found between both ears in the general population, such differences increased in people with anxiety-depressive disorders. When faced with anxiety-depressive disorders, the right ear suffered greater hearing loss than the left, showing peaks of hyper-hearing at the frequency of 4000 Hz in the anxiety subgroup, and hearing loss in the depression subgroup. In relation to anxiety, the appearance of the 4:8 pattern was observed in the right ear when the person had suffered acute stress in the 2 days prior to the audiometry, and in both ears if they had suffered stress in the 3–30 days before said stress. In conclusion, the advantage of the left ear in auditory perception was increased with these disorders, showing a hyperaudition peak in anxiety and a hearing loss in depression.

Evidence That Methylphenidate Treatment Evokes Anxiety-Like Behavior Through Glucose Hypometabolism and Disruption of the Orbitofrontal Cortex Metabolic Networks

Methylphenidate (MPH) has been widely misused by children and adolescents who do not meet all diagnostic criteria for attention-deficit/hyperactivity disorder without a consensus about the consequences. Here, we evaluate the effect of MPH treatment on glucose metabolism and metabolic network in the rat brain, as well as on performance in behavioral tests. Wistar male rats received intraperitoneal injections of MPH (2.0 mg/kg) or an equivalent volume of 0.9% saline solution (controls), once a day, from the 15th to the 44th postnatal day. Fluorodeoxyglucose-18 was used to investigate cerebral metabolism, and a cross-correlation matrix was used to examine the brain metabolic network in MPH-treated rats using micro-positron emission tomography imaging. Performance in the light-dark transition box, eating-related depression, and sucrose preference tests was also evaluated. While MPH provoked glucose hypermetabolism in the auditory, parietal, retrosplenial, somatosensory, and visual cortices, hypometabolism was identified in the left orbitofrontal cortex. MPH-treated rats show a brain metabolic network more efficient and connected, but careful analyses reveal that the MPH interrupts the communication of the orbitofrontal cortex with other brain areas. Anxiety-like behavior was also observed in MPH-treated rats. This study shows that glucose metabolism evaluated by micro-positron emission tomography in the brain can be affected by MPH in different ways according to the region of the brain studied. It may be related, at least in part, to a rewiring in the brain the metabolic network and behavioral changes observed, representing an important step in exploring the mechanisms and consequences of MPH treatment.

Cellular bases of olfactory circuit assembly revealed by systematic time-lapse imaging

Neural circuit assembly features simultaneous targeting of numerous neuronal processes from constituent neuron types, yet the dynamics is poorly understood. Here, we use the Drosophila olfactory circuit to investigate dynamic cellular processes by which olfactory receptor neurons (ORNs) target axons precisely to specific glomeruli in the ipsi- and contralateral antennal lobes. Time-lapse imaging of individual axons from 30 ORN types revealed a rich diversity in extension speed, innervation timing, and ipsilateral branch locations and identified that ipsilateral targeting occurs via stabilization of transient interstitial branches. Fast imaging using adaptive optics-corrected lattice light-sheet microscopy showed that upon approaching target, many ORN types exhibiting "exploring branches" consisted of parallel microtubule-based terminal branches emanating from an F-actin-rich hub. Antennal nerve ablations uncovered essential roles for bilateral axons in contralateral target selection and for ORN axons to facilitate dendritic refinement of postsynaptic partner neurons. Altogether, these observations provide cellular bases for wiring specificity establishment.

Hand Preference in Adults’ Referential Gestures during Storytelling: Testing for Effects of Bilingualism, Language Ability, Sex and Age

Previous studies have shown that gestures are mediated by the left hemisphere. The primary purpose of this study was to test whether most gestures are also asymmetrical, i.e., produced with the right hand. We also tested four predictors of the degree of right-hand gesture use: bilingualism, language ability, sex, and age. These factors have been related to differences in the degree of language lateralization. English monolinguals, French–English bilinguals, and French monolinguals watched a cartoon and told the story back. For the gestures they produced while speaking, we calculated the percentage produced with the right hand. As predicted, the majority of gestures were right-handed (60%). Bilingualism, language ability, and age were not significantly related to hand choice in either English or French. In English, males tended to produce more right-handed gestures than females. These results raise doubts as to whether hand preference in gestures reflects speech lateralization. We discuss possible alternative explanations for a right-hand preference.

Predation shapes behavioral lateralization: insights from an adaptive radiation of livebearing fish

Hemispheric brain lateralization can drive the expression of behavioral asymmetry, or laterality, which varies notably both within and among species. To explain these left–right behavioral asymmetries in animals, predator-mediated selection is often invoked. Recent studies have revealed that a relatively high degree of lateralization correlates positively with traits known to confer survival benefits against predators, including escape performance, multitasking abilities, and group coordination. Yet, we still know comparatively little about 1) how consistently predators shape behavioral lateralization, 2) the importance of sex-specific variation, and 3) the degree to which behavioral lateralization is heritable. Here, we take advantage of the model system of the radiation of Bahamas mosquitofish (Gambusia hubbsi) and measure behavioral lateralization in hundreds of wild fish originating from multiple blue holes that differ in natural predation pressure. Moreover, we estimated the heritability of this trait using laboratory-born fish from one focal population. We found that the degree of lateralization but not the particular direction of lateralization (left or right) differed significantly across high and low predation risk environments. Fish originating from high-predation environments were more strongly lateralized, especially females. We further confirmed a genetic basis to behavioral lateralization in this species, with significant additive genetic variation in the population examined. Our results reveal that predation risk represents one key ecological factor that has likely shaped the origin and maintenance of this widespread behavioral phenomenon, even potentially explaining some of the sex-specific patterns of laterality recently described in some animals.

Horses show individual level lateralisation when inspecting an unfamiliar and unexpected stimulus

Animals must attend to a diverse array of stimuli in their environments. The emotional valence and salience of a stimulus can affect how this information is processed in the brain. Many species preferentially attend to negatively valent stimuli using the sensory organs on the left side of their body and hence the right hemisphere of their brain. Here, we investigated the lateralisation of visual attention to the rapid appearance of a stimulus (an inflated balloon) designed to induce an avoidance reaction and a negatively valent emotional state in 77 Italian saddle horses. Horses’ eyes are laterally positioned on the head, and each eye projects primarily to the contralateral hemisphere, allowing eye use to be a proxy for preferential processing in one hemisphere of the brain. We predicted that horses would inspect the novel and unexpected stimulus with their left eye and hence right hemisphere. We found that horses primarily inspected the balloon with one eye, and most horses had a preferred eye to do so, however, we did not find a population level tendency for this to be the left or the right eye. The strength of this preference tended to decrease over time, with the horses using their non-preferred eye to inspect the balloon increasingly as the trial progressed. Our results confirm a lateralised eye use tendency when viewing negatively emotionally valent stimuli in horses, in agreement with previous findings. However, there was not any alignment of lateralisation at the group level in our sample, suggesting that the expression of lateralisation in horses depends on the sample population and testing context.

Spinal and Cerebral Integration of Noxious Inputs in Left-handed Individuals

Some pain-related information is processed preferentially in the right cerebral hemisphere. Considering that functional lateralization can be affected by handedness, spinal and cerebral pain-related responses may be different between right- and left-handed individuals. Therefore, this study aimed to investigate the cortical and spinal mechanisms of nociceptive integration when nociceptive stimuli are applied to right -handed vs. left -handed individuals. The NFR, evoked potentials (ERP: P45, N100, P260), and event-related spectral perturbations (ERSP: theta, alpha, beta and gamma band oscillations) were compared between ten right-handed and ten left-handed participants. Pain was induced by transcutaneous electrical stimulation of the lower limbs and left upper limb. Stimulation intensity was adjusted individually in five counterbalanced conditions of 21 stimuli each: three unilateral (right lower limb, left lower limb, and left upper limb stimulation) and two bilateral conditions (right and left lower limbs, and the right lower limb and left upper limb stimulation). The amplitude of the NFR, ERP, ERSP, and pain ratings were compared between groups and conditions using a mixed ANOVA. A significant increase of responses was observed in bilateral compared with unilateral conditions for pain intensity, NFR amplitude, N100, theta oscillations, and gamma oscillations. However, these effects were not significantly different between right- and left-handed individuals. These results suggest that spinal and cerebral integration of bilateral nociceptive inputs is similar between right- and left-handed individuals. They also imply that pain-related responses measured in this study may be examined independently of handedness.

Nine-month old infants' hand preference shows no link to concurrent or later vocabulary

Previous studies have shown a link between language abilities and right hand preference (RHP) for both object manipulation and pointing between 10 and 18 months of age. For infants, RHP can still be unstable. The purpose of the present study was to test whether the link between vocabulary and RHP exists among 9-month-old infants. The study included 88 infants who were observed in videotaped free-play interactions with their mothers at 9 months of age. The infants' hand preference was coded for touching objects and pointing. The children's vocabulary was measured at 9, 12, and 18 months of age. The results showed a small and significant RHP for touching objects and no significant RHP for pointing. The degree of RHP was not correlated with vocabulary scores at any age. One interpretation of these results is that, for the infants in this study, the lateralization for motor abilities was still stabilizing and therefore showed no relationship with their vocabulary. If so, this result is consistent with the argument that language lateralization builds on the lateralization for skilled and/or communicative movement.

How does hemispheric specialization contribute to human-defining cognition?

Uniquely human cognitive faculties arise from flexible interplay between specific local neural modules, with hemispheric asymmetries in functional specialization. Here, we discuss how these computational design principles provide a scaffold that enables some of the most advanced cognitive operations, such as semantic understanding of world structure, logical reasoning, and communication via language. We draw parallels to dual-processing theories of cognition by placing a focus on Kahneman's System 1 and System 2. We propose integration of these ideas with the global workspace theory to explain dynamic relay of information products between both systems. Deepening the current understanding of how neurocognitive asymmetry makes humans special can ignite the next wave of neuroscience-inspired artificial intelligence.

Age-Related Differences in Functional Asymmetry During Memory Retrieval Revisited: No Evidence for Contralateral Overactivation or Compensation

Brain asymmetry is inherent to cognitive processing and seems to reflect processing efficiency. Lower frontal asymmetry is often observed in older adults during memory retrieval, yet it is unclear whether lower asymmetry implies an age-related increase in contralateral recruitment, whether less asymmetry reflects compensation, is limited to frontal regions, or predicts neurocognitive stability or decline. We assessed age-related differences in asymmetry across the entire cerebral cortex, using functional magnetic resonance imaging data from 89 young and 76 older adults during successful retrieval, and surface-based methods allowing direct homotopic comparison of activity between cortical hemispheres . An extensive left-asymmetric network facilitated retrieval in both young and older adults, whereas diverse frontal and parietal regions exhibited lower asymmetry in older adults. However, lower asymmetry was not associated with age-related increases in contralateral recruitment but primarily reflected either less deactivation in contralateral regions reliably signaling retrieval failure in the young or lower recruitment of the dominant hemisphere-suggesting that functional deficits may drive lower asymmetry in older brains, not compensatory activity. Lower asymmetry predicted neither current memory performance nor the extent of memory change across the preceding ~ 8 years in older adults. Together, these findings are inconsistent with a compensation account for lower asymmetry during retrieval and aging.

Intra- and interhemispheric symmetry of subcortical brain structures: a volumetric analysis in the aging human brain

Here, we address the hemispheric interdependency of subcortical structures in the aging human brain. In particular, we investigated whether subcortical volume variations can be explained by the adjacency of structures in the same hemisphere or are due to the interhemispheric development of mirror subcortical structures in the brain. Seven subcortical structures in each hemisphere were automatically segmented in a large sample of 3312 magnetic resonance imaging (MRI) studies of elderly individuals in their 70s and 80s. We performed Eigenvalue analysis, and found that anatomic volumes in the limbic system and basal ganglia show similar statistical dependency whether considered in the same hemisphere (intrahemispherically) or different hemispheres (interhemispherically). Our results indicate that anatomic bilaterality of subcortical volumes is preserved in the aging human brain, supporting the hypothesis that coupling between non-adjacent subcortical structures might act as a mechanism to compensate for the deleterious effects of aging.

A novel virtual reality approach for functional lateralization in healthy adults

Functional lateralization relates to a natural asymmetry in the dominance right or left body side, and is a fundamental principle of the brain. The hemispheres of the brain control the contralateral body side, and show subtle, yet striking, anatomical asymmetries and functional lateralization. Innovative technologies, including Virtual Reality (VR), are entering the areas of experimental research, modeling and simulation related to the study of lateralization, with new perspectives of different applications in modern medical practice. Researchers/clinicians note that there are fewer VR studies with healthy participants, and which are important in evaluating/interpreting clinical outcomes, and testing the usefulness, limitations, and sensitivity of VR. The presented influence of the domination of upper/lower limbs on the performance of VR exercises was studied in healthy right-handed adults. Virtual testing sessions were performed independently with both/ dominant/ non-dominant hands, and the similar VR sessions were conduced on a Wii Balance Board (WBB) with the choice of body side, at different levels of the difficulty. The obtained results are consistent with other studies which show that cognitive-motor training in VR with the WBB platform is a very sensitive and promising tool for recognizing/assessing functional asymmetries of the right-left body side not only in disturbed lateralization, but also in the test training of healthy subjects.

Neural silences can be localized rapidly using noninvasive scalp EEG

A rapid and cost-effective noninvasive tool to detect and characterize neural silences can be of important benefit in diagnosing and treating many disorders. We propose an algorithm, SilenceMap, for uncovering the absence of electrophysiological signals, or neural silences, using noninvasive scalp electroencephalography (EEG) signals. By accounting for the contributions of different sources to the power of the recorded signals, and using a hemispheric baseline approach and a convex spectral clustering framework, SilenceMap permits rapid detection and localization of regions of silence in the brain using a relatively small amount of EEG data. SilenceMap substantially outperformed existing source localization algorithms in estimating the center-of-mass of the silence for three pediatric cortical resection patients, using fewer than 3 minutes of EEG recordings (13, 2, and 11mm vs. 25, 62, and 53 mm), as well for 100 different simulated regions of silence based on a real human head model (12 ± 0.7 mm vs. 54 ± 2.2 mm). SilenceMap paves the way towards accessible early diagnosis and continuous monitoring of altered physiological properties of human cortical function.

Evaluating cortical responses to speech in children: A functional near-infrared spectroscopy (fNIRS) study

Functional neuroimaging of speech processing has both research and clinical potential. This work is facilitating an ever-increasing understanding of the complex neural mechanisms involved in the processing of speech. Neural correlates of speech understanding also have potential clinical value, especially for infants and children, in whom behavioural assessments can be unreliable. Such measures would not only benefit normally hearing children experiencing speech and language delay, but also hearing impaired children with and without hearing devices. In the current study, we examined cortical correlates of speech intelligibility in normally hearing paediatric listeners. Cortical responses were measured using functional near-infrared spectroscopy (fNIRS), a non-invasive neuroimaging technique that is fully compatible with hearing devices, including cochlear implants. In nineteen normally hearing children (aged 6 - 13 years) we measured activity in temporal and frontal cortex bilaterally whilst participants listened to both clear- and noise-vocoded sentences targeting four levels of speech intelligibility. Cortical activation in superior temporal and inferior frontal cortex was generally stronger in the left hemisphere than in the right. Activation in left superior temporal cortex grew monotonically with increasing speech intelligibility. In the same region, we identified a trend towards greater activation on correctly vs. incorrectly perceived trials, suggesting a possible sensitivity to speech intelligibility per se, beyond sensitivity to changing acoustic properties across stimulation conditions. Outside superior temporal cortex, we identified other regions in which fNIRS responses varied with speech intelligibility. For example, channels overlying posterior middle temporal regions in the right hemisphere exhibited relative deactivation during sentence processing (compared to a silent baseline condition), with the amplitude of that deactivation being greater in more difficult listening conditions. This finding may represent sensitivity to components of the default mode network in lateral temporal regions, and hence effortful listening in normally hearing paediatric listeners. Our results indicate that fNIRS has the potential to provide an objective marker of speech intelligibility in normally hearing children. Should these results be found to apply to individuals experiencing language delay or to those listening through a hearing device, such as a cochlear implant, fNIRS may form the basis of a clinically useful measure of speech understanding.

Asymmetry of Muscle Mass Distribution and Grip Strength in Professional Handball Players

Handball is among the disciplines that impose a significant degree of asymmetry on the body movement. The aim of the study is to assess the influence of physical effort on the occurrence of asymmetry in body musculature and in isometric strength of handball players. The study examined 36 professional handball players. Players' height and body mass were measured as to calculate their body mass indexes (BMIs). Segmental bioelectrical impedance analysis (SBIA) was used to assess: the percentage of fat mass, total muscle mass (MM), musculature of the right and left side of the body, and body segments (trunk, upper and lower limbs). Moreover, grip strength was also measured. The assessment confirmed the existence of discrepancies in the right and left sides of players' bodies for the majority of the parameters. Cross-asymmetry and significant bilateral discrepancies in trunk musculature were also observed. Morphological asymmetry may impact performance in sports since it can cause unfavorable functional changes, which in turn increase the risk of injury and conditions caused by overexertion. Therefore, we believe it is important to emphasize the importance of individualized symmetrization during sports practice and consistent monitoring of the asymmetries occurring in different body parts; this should both improve one's sports results and minimize the risk of injury.

Laterality in the Cape mole-rat, Georychus capensis

Behavioural lateralization, the differential use one side of the body, and/or the bilateral use of sensory organs or limbs, is common in many vertebrates. One way in which behavioural lateralization can be detected in animals is through turning biases, which is an inherent preference to either turn left or right. Mole-rats are a unique group of mammals that demonstrate a wide range of social organizations ranging from solitary to eusociality. Behavioural asymmetry has not previously been investigated in mole-rats. In this study, captive and wild solitary Cape-mole rats (Georychus capensis) were investigated for individual (relative laterality (L_R)) and population-level (absolute laterality (L_A)) laterality. Mole-rats in the captive group were in the laboratory for at least one year, whereas the wild group were captured and experimented on within 2 weeks of capture. Animals were placed in a Y-maze facing away from the centre of the maze, and the turn towards the centre of the maze was evaluated to determine individual turning biases. Lateralized individual turning biases were more apparent in wild (7/9), compared to captive (3/10) individuals. Both captive and wild populations demonstrated a left bias, which was higher in wild animals, but not significantly so. Cape mole-rats are extremely xenophobic and aggressive, and this aggressive behaviour may underlie the turning biases in these animals, as aggression is primarily a right hemisphere dominant process. The reduced lateralization observed in captive animals may be due to a reduced need for these behaviours as a result of different environments in captivity.

The effects of hand preference and sex on right-left asymmetry in dorsal digit lengths among adults and children

BACKGROUND

Right-hand preference is related to stronger right-directional asymmetry in the length of proximal upper-limb bones, although the relationships of hand preference with directional asymmetry in phalangeal bone lengths are not known. Furthermore, dorsal digit length is an easy-to-measure, faithful proxy of X-rayed phalangeal bone length (which is costly and difficult to measure).

AIM

To study the effects of hand preference, sex, and age on right-left (R-L) asymmetry in dorsal digit lengths.

METHODS

We measured all dorsal digit lengths (except the thumb) in comparable numbers of left-handers and right-handers in samples of adults (N = 151, age: M = 22.6 years, SD = 3.3) and children (N = 65, age: M = 5.0 years, SD = 1.0).

RESULTS

Right-handers and adults had stronger right-directional asymmetry in digit lengths than left-handers and children. A Bayesian analysis yielded an 'extremely strong likelihood' of no sex differences in the R-L asymmetry of dorsal digit lengths 2 and 4.

CONCLUSIONS

The effects of hand preference, sex, and age on R-L asymmetry appear to be similar for phalangeal bone length and other (proximal) upper-limb bone lengths. Two distinct biologic mechanisms (i.e., a general right-directional asymmetry mechanism and a handedness-related directional asymmetry mechanism) may contribute to observed R-L asymmetry in limbs. Fingertip fat and bone digit length do not seem to contribute to sex differences in the R-L asymmetry (Dr-l) of the widely studied second-to-fourth digit ratio (2D:4D).

Do dolphins really have a rightward lateralization for action? The importance of behavior-specific and orientation-neutral coding

Because each side of the vertebrate body is controlled by a different side of the brain, studies of behavioral lateralization can provide insight into functional cerebral asymmetries in humans and other animals. The current study examined behavioral lateralization for a variety of behaviors in a group of 26 dolphins, in order to assess the claim that cetaceans show strong rightward action asymmetries indicative of a left-hemisphere specialization for action. We distinguished between side asymmetries and whole body turning actions, and devised a new coding system to counter the problem that previous studies of rolling behaviors (i.e., rotations around the long axis) have used contradictory coding systems depending on species' typical orientation. Our results did not support a generalized population-level rightward action asymmetry across multiple behaviors. Instead, we suggest that many dolphin behavioral asymmetries may be better explained as a result of perceptual processing asymmetries common across many vertebrates.

Comparison of Surface Area and Cortical Thickness Asymmetry in the Human and Chimpanzee Brain

Comparative study of the structural asymmetry of the human and chimpanzee brain may shed light on the evolution of language and other cognitive abilities in humans. Here we report the results of vertex-wise and ROI-based analyses that compared surface area (SA) and cortical thickness (CT) asymmetries in 3D MR images obtained for 91 humans and 77 chimpanzees. The human brain is substantially more asymmetric than the chimpanzee brain. In particular, the human brain has 1) larger total SA in the right compared with the left cerebral hemisphere, 2) a global torque-like asymmetry pattern of widespread thicker cortex in the left compared with the right frontal and the right compared with the left temporo-parieto-occipital lobe, and 3) local asymmetries, most notably in medial occipital cortex and superior temporal gyrus, where rightward asymmetry is observed for both SA and CT. There is also 4) a prominent asymmetry specific to the chimpanzee brain, namely, rightward CT asymmetry of precentral cortex. These findings provide evidence of there being substantial differences in asymmetry between the human and chimpanzee brain. The unique asymmetries of the human brain are potential neural substrates for cognitive specializations, and the presence of significant CT asymmetry of precentral gyrus in the chimpanzee brain should be further investigated.

Four meta-analyses across 164 studies on atypical footedness prevalence and its relation to handedness

Human lateral preferences, such as handedness and footedness, have interested researchers for decades due to their pronounced asymmetries at the population level. While there are good estimates on the prevalence of handedness in the population, there is no large-scale estimation on the prevalence of footedness. Furthermore, the relationship between footedness and handedness still remains elusive. Here, we conducted meta-analyses with four different classification systems for footedness on 145,135 individuals across 164 studies including new data from the ALSPAC cohort. The study aimed to determine a reliable point estimate of footedness, to study the association between footedness and handedness, and to investigate moderating factors influencing footedness. We showed that the prevalence of atypical footedness ranges between 12.10% using the most conservative criterion of left-footedness to 23.7% including all left- and mixed-footers as a single non-right category. As many as 60.1% of left-handers were left-footed whereas only 3.2% of right-handers were left-footed. Males were 4.1% more often non-right-footed compared to females. Individuals with psychiatric and neurodevelopmental disorders exhibited a higher prevalence of non-right-footedness. Furthermore, the presence of mixed-footedness was higher in children compared to adults and left-footedness was increased in athletes compared to the general population. Finally, we showed that footedness is only marginally influenced by cultural and social factors, which play a crucial role in the determination of handedness. Overall, this study provides new and useful reference data for laterality research. Furthermore, the data suggest that footedness is a valuable phenotype for the study of lateral motor biases, its underlying genetics and neurodevelopment.

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.

Handedness and White Matter Networks

The development and persistence of laterality is a key feature of human motor behavior, with the asymmetry of hand use being the most prominent. The idea that asymmetrical functions of the hands reflect asymmetries in terms of structural and functional brain organization has been tested many times. However, despite advances in laterality research and increased understanding of this population-level bias, the neural basis of handedness remains elusive. Recent developments in diffusion magnetic resonance imaging enabled the exploration of lateralized motor behavior also in terms of white matter and connectional neuroanatomy. Despite incomplete and partly inconsistent evidence, structural connectivity of both intrahemispheric and interhemispheric white matter seems to differ between left and right-handers. Handedness was related to asymmetry of intrahemispheric pathways important for visuomotor and visuospatial processing (superior longitudinal fasciculus), but not to projection tracts supporting motor execution (corticospinal tract). Moreover, the interindividual variability of the main commissural pathway corpus callosum seems to be associated with handedness. The review highlights the importance of exploring new avenues for the study of handedness and presents the latest state of knowledge that can be used to guide future neuroscientific and genetic research.

Asymmetry of Musculature and Hand Grip Strength in Bodybuilders and Martial Artists

The functional preference for the upper limb influences the occurrence of bilateral differences in other segments of the human body. The aim of the study is to assess the influence of the applied fighting technique and targeted physical effort on the occurrence of asymmetry in body musculature and isometric strength in bodybuilders and competitors of selected martial arts. Academic athletes practicing judo (J), jiu-jitsu (JJ), and bodybuilding (BB) were examined. The control group (C) consisted of students who do not practice any sports. The assessment of the body structure was conducted through segmental bioelectrical impedance analysis. Moreover, the study took into account the measurements of left- and right-hand grip strength. In judo, the uneven physical exertion of the right and left sides of the body further increases both directional and absolute asymmetry. Bilateral asymmetry of musculature in jiu-jitsu competitors and bodybuilders occurs to a lesser extent. The control group was characterized by cross-asymmetry. So as to avoid the risk of injury of sportsmen, it is important to consistently supervise and correct their body structure, which also includes the symmetrical participation of the active muscle mass in particular segments. The symmetrisation process should be individualized since each particular sportsman has their own side-to-side body morphology.

The relationship between problem-solving ability and laterality in cats

The association between hemispheric asymmetries and cognitive ability is one of the key areas of comparative laterality research. In several animal species, individual limb preferences correlate with perceptual, cognitive, or motor abilities, possibly by increasing dexterity of one limb and minimizing response conflicts between hemispheres. Despite this wealth of research, the association between laterality and cognitive abilities in the cat (Felis catus) is not well understood. Therefore, it was the aim of the present study to investigate the relationship between laterality and problem-solving ability in cats. To this end, strength and direction of paw preferences in 41 cats were measured using two novel food reaching tasks in which the animals needed to open a lid in order to reach the food reward. We found that cats that showed a clear preference for one paw were able to open more lids succesfully than ambilateral animals. Moreover, cats that preferred to interact with the test apparatus with their paw from the beginning, opened more lids than cats the first tried to interact with the test apparatus using their heads. Results also suggested a predictive validity of the first paw usage for general paw usage. It was also shown that the cats' individual paw preferences were stable and task-independent. These results yield further support to the idea that lateralization may enhance cognitive abilities.

Evidence for asymmetric inhibitory activity during motor planning phases of sensorimotor synchronization

Sensorimotor synchronization (SMS) is frequently dependent on coordination of excitatory and inhibitory activity across hemispheres, as well as the cognitive control over environmental distractors. However, the timing (motor planning versus execution) and cortical regions involved in these processes remain actively debated. Functional magnetic resonance imaging data were therefore analyzed from 34 strongly right-handed healthy adults performing a cued (to initiate motor planning) SMS task with either their right or left hand (motor execution phase) based on spatially congruent or incongruent visual stimuli. Behavioral effects of incongruent stimuli were limited to the first stimulus. Functionally, greater activation was observed in left sensorimotor cortex (SMC) and right cerebellar Lobule V for congruent versus incongruent stimuli. A negative blood-oxygen level dependent response, a putative marker of neural inhibition, was present in bilateral SMC, right supplemental motor area (SMA) and bilateral cerebellar Lobule V during the motor planning, but not execution phase. The magnitude of the inhibitory response was greater in right cortical regions and cerebellar Lobule V. Homologue connectivity was associated with inhibitory activity in the right SMA, suggesting that individual differences in intrinsic connectivity may mediate transcallosal inhibition. In summary, results suggest increased inhibition (i.e., greater negative BOLD response) within the right relative to left hemisphere, which was released once motor programs were executed. Both task and intrinsic functional connectivity results highlight a critical role of the left SMA in interhemispheric inhibition and motor planning.

Fluctuating asymmetry in patients with schizophrenia is related to hallucinations and thought disorganisation

Fluctuating asymmetry represents the degree to which the right and left side of the body are asymmetrical, and is a sign of developmental instability. Higher levels of fluctuating asymmetry have been observed in individuals within the schizophrenia spectrum. We aimed to explore the associations of fluctuating asymmetry with psychotic and affective symptoms in schizophrenia patients, as well as with propensity to these symptoms in non-clinical individuals. A measure of morphological fluctuating asymmetry was calculated for 39 patients with schizophrenia and 60 healthy individuals, and a range of clinical and subclinical psychiatric symptoms was assessed. Regression analyses of the fluctuating asymmetry measure were conducted within each group. In the patient cohort, fluctuating asymmetry was significantly associated with the hallucination and thought disorganisation scores. T-test comparisons revealed that the patients presenting either hallucinations or thought disorganisation were significantly more asymmetrical than were the healthy individuals, while the patients without these key symptoms were equivalent to the healthy individuals. A positive association with the anxiety score emerged in a subsample of 36 healthy participants who were rated on affective symptoms. These findings suggest that fluctuating asymmetry may be an indicator of clinical hallucinations and thought disorganisation rather than an indicator of schizophrenia disease.

A function for the bicameral mind

Why do the left and right sides of the brain have different functions? Having a lateralized brain, in which each hemisphere processes sensory inputs differently and carries out different functions, is common in vertebrates, and it has now been reported for invertebrates too. Experiments with several animal species have shown that having a lateralized brain can enhance the capacity to perform two tasks at the same time. Thus, the different specializations of the left and right sides of the brain seem to increase brain efficiency. Other advantages may involve control of action that, in Bilateria, may be confounded by separate and independent sensory processing and motor outputs on the left and right sides. Also, the opportunity for increased perceptual training associated with preferential use of only one sensory or motoric organ may result in a time advantage for the dominant side. Although brain efficiency of individuals can be achieved without the need for alignment of lateralization in the population, lateral biases (such as preferences in the use of a laterally-placed eye) usually occur at the population level, with most individuals showing a similar direction of bias. Why is this the case? Not only humans, but also most non-human animals, show a similar pattern of population bias (i.e., directional asymmetry). For instance, in several vertebrate species (from fish to mammals) most individuals react faster when a predator approaches from their left side, although some individuals (a minority usually ranging from 10 to 35%) escape faster from predators arriving from their right side. Invoking individual efficiency (lateralization may increase fitness), evolutionary chance or simply genetic inheritance cannot explain this widespread pattern. Using mathematical theory of games, it has been argued that the population structure of lateralization (with either antisymmetry or directional asymmetry) may result from the type of interactions asymmetric organisms face with each other.

Cerebral asymmetry during development using linear measures from MRI

Asymmetry of the human brain is a well-known phenomenon, but the nature and extent of these differences throughout postnatal development have not been examined. Accordingly, linear measurements of the brains of 121 infants, children, and adolescents were determined to ascertain cerebral hemispheric asymmetries. Using multiple statistical methods, the results showed that: 1) the frontal lobe is wider on the right, while the occipital lobe is wider on the left; 2) there are no side to side differences in cerebral hemispheric length or height; and 3) there are no major sex differences. Especially notable is the lack of any correlation between side to side differences in length, width, or height and increasing age, which was also the case for cerebral hemispheric area or volume with increasing age. Regarding petalias: 1) the right frontal petalia occurs in 61%, the left occipital in 60%, and both petalias in 36% of the cohort; 2) the right frontal and left occipital petalias are of similar lengths; 3) the distances of both petalias increase with advancing age but not when scaled to either cerebral hemispheric area or volume, indicating that petalias are equally prominent early in postnatal life compared to later development; and 4) there are no major sex differences in the frequency or magnitude of either petalia. These findings provide comprehensive new information regarding age and sex related cerebral hemispheric asymmetries during development.

From Science to Practice: A Review of Laterality Research on Ungulate Livestock

In functional laterality research, most ungulate livestock species have until recently been mainly overlooked. However, there are many scientific and practical benefits of studying laterality in ungulate livestock. As social, precocial and domestic species, they may offer insight into the mechanisms involved in the ontogeny and phylogeny of functional laterality and help to better understand the role of laterality in animal welfare. Until now, most studies on ungulate livestock have focused on motor laterality, but interest in other lateralized functions, e.g., cognition and emotions, is growing. Increasingly more studies are also focused on associations with age, sex, personality, health, stress, production and performance. Although the full potential of research on laterality in ungulate livestock is not yet exploited, findings have already shed new light on central issues in cognitive and emotional processing and laid the basis for potentially useful applications in future practice, e.g., stress reduction during human-animal interactions and improved assessments of health, production and welfare. Future research would benefit from further integration of basic laterality methodology (e.g., testing for individual preferences) and applied ethological approaches (e.g., established emotionality tests), which would not only improve our understanding of functional laterality but also benefit the assessment of animal welfare.

Laterality as a Tool for Assessing Breed Differences in Emotional Reactivity in the Domestic Cat, Felis silvestris catus

Simple Summary

Cat breeds differ enormously in their emotional reactivity, a factor that can impact upon the success of the pet-owner relationship, with indirect consequences for animal welfare. Traditional methods of assessing emotional reactivity in cats have focused largely on questionnaire-based assessments of breed-specific behavioural profiles. We explored whether paw preferences, which have been linked to emotional reactivity in animals, are related to cat breed. The paw preferences of 4 commonly owned cat breeds were tested on a food-reaching challenge. Cats’ paw preferences differed between the breeds. Bengal cats were more likely to show a left-sided paw preference than other breeds, whilst Persians showed the weakest paw preferences, veering more heavily towards ambilaterality. Results confirmed our earlier work in showing a strong tendency for left paw use in male cats and right paw use in females. We propose that paw preference measurement could provide a useful method for assessing emotional reactivity in domestic cats, adding to our currently limited artillery of tools for determining breed-specific profiles. Such information would be of benefit to individuals considering the acquisition of a new cat, and, in the longer term may help to foster more successful cat-owner relationships, leading to indirect benefits to feline welfare.

Abstract

Cat breeds differ enormously in their behavioural disposition, a factor that can impact on the pet-owner relationship, with indirect consequences for animal welfare. This study examined whether lateral bias, in the form of paw preference, can be used as a tool for assessing breed differences in emotional reactivity in the cat. The paw preferences of 4 commonly owned breeds were tested using a food-reaching challenge. Cats were more likely to be paw-preferent than ambilateral. Maine Coons, Ragdolls and Bengals were more likely to be paw-preferent than ambilateral, although only the Bengals showed a consistent preference for using one paw (left) over the other. The strength of the cats’ paw use was related to cat breed, with Persians being more weakly lateralised. Direction of paw use was unrelated to feline breed, but strongly sex-related, with male cats showing a left paw preference and females displaying a right-sided bias. We propose that paw preference measurement could provide a useful method for assessing emotional reactivity in domestic cats. Such information would be of benefit to individuals considering the acquisition of a new cat, and, in the longer term, may help to foster more successful cat-owner relationships, leading to indirect benefits to feline welfare.

Evaluating time-reversed speech and signal-correlated noise as auditory baselines for isolating speech-specific processing using fNIRS

Evidence using well-established imaging techniques, such as functional magnetic resonance imaging and electrocorticography, suggest that speech-specific cortical responses can be functionally localised by contrasting speech responses with an auditory baseline stimulus, such as time-reversed (TR) speech or signal-correlated noise (SCN). Furthermore, these studies suggest that SCN is a more effective baseline than TR speech. Functional near-infrared spectroscopy (fNIRS) is a relatively novel, optically-based imaging technique with features that make it ideal for investigating speech and language function in paediatric populations. However, it is not known which baseline is best at isolating speech activation when imaging using fNIRS. We presented normal speech, TR speech and SCN in an event-related format to 25 normally-hearing children aged 6-12 years. Brain activity was measured across frontal and temporal brain areas in both cerebral hemispheres whilst children passively listened to the auditory stimuli. In all three conditions, significant activation was observed bilaterally in channels targeting superior temporal regions when stimuli were contrasted against silence. Unlike previous findings in infants, we found no significant activation in the region of interest over superior temporal cortex in school-age children when normal speech was contrasted against either TR speech or SCN. Although no statistically significant lateralisation effects were observed in the region of interest, a left-sided channel targeting posterior temporal regions showed significant activity in response to normal speech only, and was investigated further. Significantly greater activation was observed in this left posterior channel compared to the corresponding channel on the right side under the normal speech vs SCN contrast only. Our findings suggest that neither TR speech nor SCN are suitable auditory baselines for functionally isolating speech-specific processing in an experimental set up involving fNIRS with 6-12 year old children.