Anatomical Asymmetries Research Articles

Anatomic and functional asymmetries interactively shape human early visual cortex responses.

Early visual processing is surprisingly flexible even in the adult brain. This flexibility involves both long-term structural plasticity and online adaptations conveyed by top-down feedback. Although this view is supported by rich evidence from both human behavioral studies and invasive electrophysiology in nonhuman models, it has proven difficult to close the gap between species. In particular, it remains debated whether noninvasive measures of neural activity can capture top-down modulations of the earliest stages of processing in the human visual cortex. We previously reported modulations of retinotopic C1, the earliest component of the human visual evoked potential. However, these effects were selectively observed in the upper visual field (UVF). Here we test whether this asymmetry is linked to an interaction between differences in spatial resolution across the visual field and the specific stimuli used in previous studies. We measured visual evoked potentials in response to task-irrelevant, high-contrast textures of different densities in a comparatively large sample of healthy volunteers (N = 31) using high-density electroencephalogram. Our results show differential response profiles for upper and lower hemifields, with UVF responses saturating at higher stimulus densities. In contrast, lower visual field responses did not increase, and even showed a tendency toward a decrease at the highest density tested. We propose that these findings reflect feature- and task-specific pooling of signals from retinotopic regions with different sensitivity profiles. Such complex interactions between anatomic and functional asymmetries need to be considered to resolve whether human early visual cortex activity is modulated by top-down factors.

Contextual Modulation in Mammalian Neocortex is Asymmetric

Neural systems are composed of many local processors that generate an output given their many inputs as specified by a transfer function. This paper studies a transfer function that is fundamentally asymmetric and builds on multi-site intracellular recordings indicating that some neocortical pyramidal cells can function as context-sensitive two-point processors in which some inputs modulate the strength with which they transmit information about other inputs. Learning and processing at the level of the local processor can then be guided by the context of activity in the system as a whole without corrupting the message that the local processor transmits. We use a recent advance in the foundations of information theory to compare the properties of this modulatory transfer function with that of the simple arithmetic operators. This advance enables the information transmitted by processors with two distinct inputs to be decomposed into those components unique to each input, that shared between the two inputs, and that which depends on both though it is in neither, i.e., synergy. We show that contextual modulation is fundamentally asymmetric, contrasts with all four simple arithmetic operators, can take various forms, and can occur together with the anatomical asymmetry that defines pyramidal neurons in mammalian neocortex.

Human Anatomical Database for Forensic Analysis of Pre‐Mortem versus Post‐Mortem Exsanguination

This study was performed to address questions raised by an exsanguination homicide and to better understand the circumstances and patterns associated with cases of extreme blood loss. Few datasets applicable to exsanguination cases exist in the literature; thus, this work is also intended to expand the resources available for understanding human blood loss and blood removal more generally. A comprehensive dataset was generated analyzing variation in blood evacuation within a set of fourteen vascular structures from 105 human cadaveric bodies. Bodies were stored and embalmed using a standardized methodology, with both superficial and deep vessels, across a wide size range. Vessels were dissected and assessed for the presence of residual blood post‐embalming. Because the blood was flushed as part of the embalming procedure itself, these measurements are indicative of blood evacuation in a fresh tissue specimen (i.e. prior to embalming). Even with multiple points of perfusion, an external pump, and large volumes of embalming fluid, most vessels remained unevacuated of blood in all individuals.The intercostal arteries were by far the most commonly evacuated vessels, where a refined approach found that the fourth right posterior intercostal artery was empty of blood in over 30% of cases. The next most commonly evacuated vessels were the cephalic vein (3.81% aggregate) and the right coronary artery (RCA) (2.86% aggregate, 8.57% 2018 subset). Atria were individually empty at comparatively high rates (12.9%) but only in three cases were both the right and left atria empty in the same individual. A few sampled cardiovascular structures have significantly correlated rates of evacuation, though the correlation coefficients are not large. Cephalic and basilic vein evacuation are coupled (Pearson Coefficient of 0.56, p<0.0001), which is likely a result of their similar function, depth, and size. Atrial evacuation was correlated with both intercostal artery evacuation and RCA evacuation. Asymmetry in evacuation rates was noted between the left and right IJV (5.9% and 2.9%, respectively) and the left and right coronary arteries (0% and 8.6%, respectively). These patterns might be the result of asymmetry in injection site, anatomical asymmetry, or an interaction of the two factors.The overall aggregate rate of evacuation per vascular structure was only 1.97%. It was concluded that complete or nearly complete evacuation of intravascular blood volume is effectively impossible in a post‐mortem context without extraordinary circumstances. In conjunction with other lines of evidence, this controlled dataset could be useful as one standard of comparison for future cases involving death due to exsanguination. This database may also be of interest to anyone performing embalming, utilizing cadaveric human donors in medical education, or utilizing cadaveric samples as proxies for understanding vascular health.Support or Funding InformationAccess to donors and permission for their use in research was graciously provided by the Anatomical Gift Program of USC

Brain and Behavioral Asymmetry: A Lesson From Fish

It is widely acknowledged that the left and right hemispheres of human brains display both anatomical and functional asymmetries. For more than a century, brain and behavioral lateralization have been considered a uniquely human feature linked to language and handedness. However, over the past decades this idea has been challenged by an increasing number of studies describing structural asymmetries and lateralized behaviors in non-human species extending from primates to fish. Evidence suggesting that a similar pattern of brain lateralization occurs in all vertebrates, humans included, has allowed the emergence of different model systems to investigate the development of brain asymmetries and their impact on behavior. Among animal models, fish have contributed much to the research on lateralization as several fish species exhibit lateralized behaviors. For instance, behavioral studies have shown that the advantages of having an asymmetric brain, such as the ability of simultaneously processing different information and perform parallel tasks compensate the potential costs associated with poor integration of information between the two hemispheres thus helping to better understand the possible evolutionary significance of lateralization. However, these studies inferred how the two sides of the brains are differentially specialized by measuring the differences in the behavioral responses but did not allow to directly investigate the relation between anatomical and functional asymmetries. With respect to this issue, in recent years zebrafish has become a powerful model to address lateralization at different level of complexity, from genes to neural circuitry and behavior. The possibility of combining genetic manipulation of brain asymmetries with cutting-edge in vivo imaging technique and behavioral tests makes the zebrafish a valuable model to investigate the phylogeny and ontogeny of brain lateralization and its relevance for normal brain function and behavior.

EEG Effective Source Projections Are More Bilaterally Symmetric in Infants Than in Adults

Although anatomical brain hemispheric asymmetries have been clearly documented in the infant brain, findings concerning functional hemispheric specialization have been inconsistent. The present report aims to assess whether bilaterally symmetric synchronous activity between the two hemispheres is a characteristic of the infant brain. To asses cortical bilateral synchronicity, we used decomposition by independent component analysis (ICA) of high-density electroencephalographic (EEG) data collected in an auditory passive oddball paradigm. Decompositions of concatenated 64-channel EEG data epochs from each of 34 typically developing 6-month-old infants and from 18 healthy young adults participating in the same passive auditory oddball protocol were compared to characterize differences in functional brain organization between early life and adulthood. Our results show that infant EEG decompositions comprised a larger number of independent component (IC) effective source processes compatible with a cortical origin and having bilaterally near-symmetric scalp projections (13.8% of the infant data ICs presented a bilateral pattern vs. 4.3% of the adult data ICs). These IC projections could be modeled as the sum of potentials volume-conducted to the scalp from synchronous locally coherent field activities in corresponding left and right cortical source areas. To conclude, in this paradigm, source-resolved infant brain EEG exhibited more bilateral synchronicity than EEG produced by the adult brain, supporting the hypothesis that more strongly unilateral and likely more functionally specialized unihemispheric cortical field activities are concomitants of brain maturation.

Variation and Correlations in Departures from Symmetry of Brain Torque, Humeral Morphology and Handedness in an Archaeological Sample of Homo sapiens

The anatomical asymmetries of the human brain are the subject of a great deal of scientific interest because of their links with handedness and lateralized cognitive functions. Information about lateralization in humans is also available from the post-cranial skeleton, particularly the arm bones, in which differences in size and shape are related to hand/arm preference. Our objective here is to characterize the possible correlations between the endocranial and post-cranial asymmetries of an archaeological sample. This, in turn, will allow us to try to identify and interpret prospective functional traits in the archaeological and fossil records. We observe that directional asymmetry (DA) is present both for some endocranial and humeral traits because of brain lateralization and lateralized behaviors, while patterns of fluctuating asymmetry (FA) vary. The combined study of these anatomical elements and of their asymmetries can shed light on the ways in which the body responds to dependent asymmetrical stimuli across biologically independent anatomical areas. Variations in FA are, in this context, indicators of differences in answers to lateralized factors. Humeri tend to show a much larger range of variation than the endocast. We show that important but complex information may be extracted from the combined study of the endocast and the arms in an archaeological sample of Homo sapiens.

Visual field deficits following laser ablation of the hippocampus.

To qualify the incidence of and risk factors for visual field deficits (VFD) following laser interstitial thermal ablation (LITT) for mesial temporal lobe epilepsy (MTLE) and to relate this to anterior temporal lobectomy (ATL). Fifty-seven patients underwent LITT of the amygdalo-hippocampal complex (AH) for MTLE. Masks of ablation volumes, laser probe trajectories, and visual radiations (VRs) from individual subject space were transformed into standardized space using nonlinear registration. Voxel-wise statistics were performed to model relationships between VFDs vs ablation volumes, laser trajectories, VRs, and AH asymmetry. A review of VFDs following ATLs was performed. The incidence of VFD after LITT is much lower than after ATLs. A total of 37.5% of patients developed a VFD, with the probability of this being much higher after left (50%) vs right hemisphere LITT (10%) (Fisher test, p = 0.05). This laterality effect on VFDs is mirrored but underappreciated in ATL series. The most consistent LITT-VFD occurred in the superior vertical octant. Ablation of Meyer loop as well as the summed probability of VRs within laser trajectories correlated with VFDs (p < 0.05). Left and right hippocampi have significantly distinct orientations in axial and coronal planes, which may be one reason for the variation in VFD probability. LITT results in lower rates of and smaller VFDs-typically an octantanopsia. VRs are at greater risk during surgery for left than right MTLE. Anatomical asymmetries in hippocampal anatomy may explain the hemispheric differences in deficits, and should factor into trajectory planning and also into preoperative patient counseling. Overall the incidence and extent of visual deficits following LITT for MTLE is lower than the reported data following anterior temporal lobectomy. VF tractography incorporated into LITT planning may reduce the occurrence of VFDs.

Identifying and characterizing projections from the subthalamic nucleus to the cerebellum in humans

A connection between the subthalamic nucleus (STN) and the cerebellum which has been shown to exist in non-human primates, was recently identified in humans. However, its anatomical features, network properties and function have yet to be elucidated in humans. In the present study, we quantified the STN-cerebellum pathway in humans and explored its function based on structural observations. Anatomical features and asymmetry index (AI) were explored using high definition fiber tractography data of 30 individuals from the Massachusetts General Hospital – Human Connectome Project adult diffusion database. Pearson’s correlation analysis was performed to determine the interrelationship between the subdivisions of the STN-cerebellum and the global cortical-STN connections. The pathway was visualized bilaterally in all the subjects. Typically, after setting out from the STN, the STN-cerebellum projections incorporated into the nearby corticopontine tracts, passing through the cerebral peduncle, mediated by the pontine nucleus and then connecting in two opposite directions to join the bilateral middle cerebellar peduncle. On the group averaged level, 78.03% and 62.54% of fibers from the right and left STN respectively, distributed to Crus I in the cerebellum, part of the remaining fibers projected to Crus II, with most of the fibers crossing contralaterally. According to the AI evaluation, 60% of the participants were right STN dominant, 23% were left STN dominant, and 17% were relatively symmetric. Pearson’s correlation analysis further indicated that the number of pathways from mesial Brodmann area 8 to the STN (hyperdirect pathway associated with decision making) was positively correlated with the number of fibers from the right STN to Crus I. The insertion and termination, the right-side dominance, and the positive correlation with the hyperdirect pathway all suggest that the STN-cerebellum pathway might be involved in decision-making processes.

Chapter 10 - Development of handedness, anatomical and functional brain lateralization

The present chapter offers a report on the recent literature on the neural bases of hemispheric specialization (HS), anatomical and functional developmental timecourse of HS, and on the available knowledge of their relationships with the development of handedness. Strong anatomical asymmetries can be seen located along the end of the sylvian fissure and the superior temporal sulcus (STS) as soon as the 23rd gestational week. They correspond to a leftward sulcal depth asymmetry of the Sylvian fissure coupled with a rightward asymmetry of STS. These neonatal asymmetries targeting speech processing areas do not further change with development. Different from these anatomical asymmetries, the functional asymmetries of language areas develop during childhood. Such a development is characterized at birth by a predominant interhemispheric intrinsic connectivity between homotopic areas that will evolve toward left hemisphere intrahemispheric intrinsic connectivity between anterior and posterior language poles. The development of such a typical architecture of language networks in the left hemisphere dominant for language in more than 90% of humans translates into a continuous increase in the leftward asymmetries of activation during language production throughout childhood. With regard to the rightward cerebral lateralization for visuospatial functions, neuroimaging studies tend to indicate an increase in rightward lateralization of frontal-parietal network with age during visuospatial memory and visuospatial search tasks. In addition, the spatial-attentional behavioral asymmetries emerge early (in preschool children) and, then, can be modulated by factors linked to motor asymmetry and handedness. Finally, the study of manual lateralization in relation to language development has shown the importance of considering several characteristics of manual activities. In particular, the dissociation between manipulative activities and communicative gestures in young children may open further perspectives for future research on HS.

Bilateral asymmetries in male and female young elite fencers in relation to fencing performance

BACKGROUND: Data about lower extremities’ strength and power asymmetries in fencers, and their relationships to fencing performance are limited and inconsistent. OBJECTIVE: The aim of the present study was to investigate asymmetries, between dominant (D) and non-dom (ND) legs of elite young male and female fencers, in relation to performance in fencing specific tests. METHODS: Anthropometric characteristics, unilateral vertical-horizontal jumping, isokinetic strength, lunge and step lunge performances were evaluated in 16 male and 22 female elite fencers. RESULTS: Significant differences between genders were found for all anthropometric measurements (p&lt; 0.05). No significant bilateral asymmetries and gender x laterality effects were observed (p&gt; 0.05). Fencing performance was negatively correlated with the D leg’s flexion/extension (F/E) ratio at 300∘/s (r: -0.564 to -0.619, p&lt; 0.05). In addition, D leg’s F/E ratio at 300∘/s was positively related to lung peak velocity and power in female fencers (r: 0.562–0.649; p&lt; 0.05). Finally, only in female fencers, unilateral triple hop distance was significantly related to lung peak velocity and power (r: 0.442–0.500; p&lt; 0.05). CONCLUSIONS: The results of the present study suggest that the differential activation/movement pattern of the D and ND leg muscles do not lead to anatomical, dynamic and functional lower extremities asymmetries.

Simulations of particle tracking in the oligociliated mouse node and implications for left-right symmetry-breaking mechanics.

The concept of internal anatomical asymmetry is familiar-usually in humans the heart is on the left and the liver is on the right; however, how does the developing embryo know to produce this consistent laterality? Symmetry-breaking initiates with left-right asymmetric cilia-driven fluid mechanics in a small fluid-filled structure called the ventral node in mice. However, the question of what converts this flow into left-right asymmetric development remains unanswered. A leading hypothesis is that flow transports morphogen-containing vesicles within the node, the absorption of which results in asymmetrical gene expression. To investigate how vesicle transport might result in the situs patterns observe in wild-type and mutant experiments, we extend the open-source Stokes flow package, NEAREST, to consider the hydrodynamic and Brownian motion of particles in a mouse model with flow driven by one, two and 112 beating cilia. Three models for morphogen-containing particle released are simulated to assess their compatibility with observed results in oligociliated and wild-type mouse embryos: uniformly random release, localized cilium stress-induced release and localized release from motile cilia themselves. Only the uniformly random release model appears consistent with the data, with neither localized release model resulting in significant transport in the oligociliated embryo. This article is part of the Theo Murphy meeting issue 'Unity and diversity of cilia in locomotion and transport'.

No Alterations of Brain Structural Asymmetry in Major Depressive Disorder: An ENIGMA Consortium Analysis.

Asymmetry is a subtle but pervasive aspect of the human brain, and it may be altered in several psychiatric conditions. MRI studies have shown subtle differences of brain anatomy between people with major depressive disorder and healthy control subjects, but few studies have specifically examined brain anatomical asymmetry in relation to this disorder, and results from those studies have remained inconclusive. At the functional level, some electroencephalography studies have indicated left fronto-cortical hypoactivity and right parietal hypoactivity in depressive disorders, so aspects of lateralized anatomy may also be affected. The authors used pooled individual-level data from data sets collected around the world to investigate differences in laterality in measures of cortical thickness, cortical surface area, and subcortical volume between individuals with major depression and healthy control subjects. The authors investigated differences in the laterality of thickness and surface area measures of 34 cerebral cortical regions in 2,256 individuals with major depression and 3,504 control subjects from 31 separate data sets, and they investigated volume asymmetries of eight subcortical structures in 2,540 individuals with major depression and 4,230 control subjects from 32 data sets. T1-weighted MRI data were processed with a single protocol using FreeSurfer and the Desikan-Killiany atlas. The large sample size provided 80% power to detect effects of the order of Cohen's d=0.1. The largest effect size (Cohen's d) of major depression diagnosis was 0.085 for the thickness asymmetry of the superior temporal cortex, which was not significant after adjustment for multiple testing. Asymmetry measures were not significantly associated with medication use, acute compared with remitted status, first episode compared with recurrent status, or age at onset. Altered brain macro-anatomical asymmetry may be of little relevance to major depression etiology in most cases.

Anatomy of leaf edges in Marantaceae in the Neotropics: the relationship between vernation and leaf asymmetry and contributions to the systematics of the family

AbstractMarantaceae consist of species with asymmetric leaves of two types: those with either a wider left or right half; this asymmetry is related, respectively, to clockwise or counterclockwise convolute vernation. In this study, we analysed whether anatomical differences in the leaf edges, i.e. the anatomical asymmetry, were related to the orientation of the convolute vernation and to the asymmetry of leaf morphology, and whether these differences supported the organization of the clades in the family. Transverse sections of the mid third of the leaf buds expanded to the height of the right and left edges of the blades were prepared for 19 species belonging to 11 genera, using cyto-histological techniques. Anatomical analyses of the blade edges revealed that there is a relationship between morphological asymmetry and anatomical asymmetry that has never before been ascribed to the family. The anatomical data support differences between the arrangements in two of the three Neotropical informal groups. In the Calathea clade, Calathea showed much more similarity with Goeppertia than with Ischnosiphon and Monotagma, since they are the only genera that do not present with anatomical asymmetry. In the Maranta clade, Ctenanthe, Saranthe and Stromanthe appear to be related to one another, as they share strong anatomical asymmetry and fibrous edges. These characteristics, however, are not observed in Myrosma, which in turn is more anatomically similar to Maranta.

Characteristics of body balance disorder in children with unilateral lower limb shortening

Background. In modern orthopedics, the problem of unilateral shortening of the lower limbs in children is extremely important. In the process of child growth, there occurs progression of the shortened segment, which leads to anatomical asymmetry of the lower limbs and an increase in the imbalance of the limb load. Secondary deformities of the pelvis and spine aggravate the patients disability. The features of abnormal postural balance of the body depending on the etiology of the disease, such as congenital or acquired, as well as the degree of preservation of motor stereotypes in children with unilateral shortening of the lower limbs, are still understudied.&#x0D; Aim. The aims of this work are to study postural stability in children with unilateral shortening of the lower limbs and to assess the disorders of body balance depending on the etiology of the lesion.&#x0D; Materials and methods. The standard stabilometric values of 11 healthy children (average age, 11.9 0.73 years) were determined (group 1), as well as the statokinesiogram parameters in 22 patients with unilateral shortening of the lower limb. The second group included 11 children (average age, 11.9 1.05 years) with congenital shortening of the lower limb (average shortening, 4.8 0.8 cm). The third group also consisted of 11 children (average age, 12.2 0.78 years), but with acquired shortening of the lower limb (average shortening, 4.5 0.38 cm). Statistical research included correlation analysis.&#x0D; Results. A significant decrease in the stability of the vertical balance was observed in both groups of patients, which was demonstrated by pronounced deviations from the nominal values of stabilometric parameters, compared with healthy children: an increased center of pressure displacement, large values of the statokinesiogram area, and the length of the pressure displacement path. It was possible to determine the state of adaptive postural mechanisms for assessing the formation of the degree of adequacy of the motor strategy in patients with unilateral shortening of the lower limb, depending on the etiology of the lesion, owing to the method of stabilometry.&#x0D; Conclusion. An appropriate adaptive motor stereotype has been formed in patients with acquired shortening of the lower limb; in the new conditions, the system for ensuring postural balance is stabilized. There is a different strategy for maintaining posture stability characterized by a nonoptimal motor stereotype in patients with congenital shortening of the lower limb. The stabilometric assessment of the asymmetry of the lower limb load is a promising method for studying the formation of compensatory mechanisms for controlling the locomotion system, which is important when planning rehabilitation measures.

Hand preference and local asymmetry in cerebral cortex, basal ganglia, and cerebellar white matter.

Hand preference is a striking example of functional lateralization, with 90% of the population preferentially using their right hand. However, the search for brain structural correlates of this lateralization has produced inconsistent results. While large-scale neuroimaging studies using automated methods have largely failed to find local anatomical asymmetries associated with hand preference, other studies identifying specific motor regions have been able to find local morphological and functional differences. The present study looked at brain asymmetries in the brain's motor system using established cortical landmarks to identify the somatomotor hand region and extracted regional volumes of subcortical and cerebellar regions. Our results showed a strong left-right asymmetry in the cortical hand region, with weaker asymmetries appearing in the striatum and cerebellar white matter. Such asymmetries were much more pronounced in right-handers, whereas much weaker or absent lateralizing effects were observed in left-handed subjects. This study demonstrates the importance of local landmarks in studying individual anatomical differences. More generally, establishing structural correlates of hand preference is important, as this could further establish the origins of cerebral lateralization.

Multiple Pathways Act Together To Establish Asymmetry of the Ventral Nerve Cord in Caenorhabditis elegans.

The central nervous system of most animals is bilaterally symmetrical. Closer observation often reveals some functional or anatomical left-right asymmetries. In the nematode Caenorhabditis elegans, the most obvious asymmetry in the nervous system is found in the ventral nerve cord (VNC), where most axons are in the right axon tract. The asymmetry is established when axons entering the VNC from the brain switch from the left to the right side at the anterior end of the VNC. In genetic screens we identified several mutations compromising VNC asymmetry. This includes alleles of col-99 (encoding a transmembrane collagen), unc-52/perlecan and unc-34 (encoding the actin modulator Enabled/Vasodilator-stimulated phosphoproteins). In addition, we evaluated mutants in known axon guidance pathways for asymmetry defects and used genetic interaction studies to place the genes into genetic pathways. In total we identified four different pathways contributing to the establishment of VNC asymmetry, represented by UNC-6/netrin, SAX-3/Robo, COL-99, and EPI-1/laminin. The combined inactivation of these pathways in triple and quadruple mutants leads to highly penetrant VNC asymmetry defects, suggesting these pathways are important contributors to the establishment of VNC asymmetry in C. elegans.

Handedness in monkeys reflects hemispheric specialization within the central sulcus. An in vivo MRI study in right- and left-handed olive baboons

Handedness, one of the most prominent expressions of laterality, has been historically considered unique to human. This noteworthy feature relates to contralateral inter-hemispheric asymmetries in the motor hand area following the mid-portion of the central sulcus. However, within an evolutionary approach, it remains debatable whether hand preferences in nonhuman primates are associated with similar patterns of hemispheric specialization. In the present study conducted in Old world monkeys, we investigate anatomical asymmetries of the central sulcus in a sample of 86 olive baboons (Papio anubis) from in vivo T1 anatomical magnetic resonance images (MRI). Out of this sample, 35 individuals were classified as right-handed and 28 as left-handed according to their hand use responses elicited by a bimanual coordinated tube task. Here we report that the direction and degree of hand preference (left or right), as measured by this manual task, relates to and correlates with contralateral hemispheric sulcus depth asymmetry, within a mid-portion of the central sulcus. This neuroanatomical manifestation of handedness in baboons located in a region, which may correspond to the motor hand area, questions the phylogenetic origins of human handedness that may date back to their common ancestor, 25–40 millions years ago.

Motor Lateralization May Be Influenced by Long-Term Piano Playing Practice.

Motor lateralization is viewed as anatomical or functional asymmetry of the two sides of the body. Functional motor asymmetry can be influenced by musical practice. This study explored whether piano playing experience modulates motor asymmetry and leads to an altered pattern of hand selection, reflecting an altered handedness. We asked two groups of right-handed participants-piano players and non-piano players-to reach targets in their frontal space with both arms, and we tested the motor performance of each arm on this task and then on an arm preference test. As musical practice can decrease motor asymmetry between arms, we hypothesized that participants with piano playing experience would display less interlimb asymmetry and that this, in turn, would change their arm preference pattern, compared with participants without piano playing experience. We found support for both hypotheses, and we conclude that arm selection (preference) is not biologically fixed, but, rather, can be modulated through long-term piano playing.

Improved wide-field emmetropic human eye model based on ocular wavefront measurements and geometry-independent gradient index lens.

There is a need to better understand the peripheral optics of the human eye and their correction. Current eye models have some limitations to accurately predict the wavefront errors for the emmetropic eye over a wide field. The aim here was to develop an anatomically correct optical model of the human eye that closely reproduces the wavefront of an average Caucasian-only emmetropic eye across a wide visual field. Using an optical design program, a schematic eye was constructed based on ocular wavefront measurements of the right eyes of thirty healthy young emmetropic individuals over a wide visual field (from 40° nasal to 40° temporal and up to 20° inferior field). Anatomical parameters, asymmetries, and dispersion properties of the eye's different optical components were taken into account. A geometry-independent gradient index model was employed to better represent the crystalline lens. The RMS wavefront error, wavefront shapes, dominant Zernike coefficients, nasal-temporal asymmetries, and dispersion properties of the developed schematic eye closely matched the corresponding measured values across the visual field. The developed model can help in the design of wide-field ophthalmic instruments and is useful in the study and simulations of the peripheral optics of the human eye.

A thyroid hormone regulated asymmetric responsive centre is correlated with eye migration during flatfish metamorphosis

Flatfish metamorphosis is a unique post-embryonic developmental event in which thyroid hormones (THs) drive the development of symmetric pelagic larva into asymmetric benthic juveniles. One of the eyes migrates to join the other eye on the opposite side of the head. Developmental mechanisms at the basis of the acquisition of flatfish anatomical asymmetry remain an open question. Here we demonstrate that an TH responsive asymmetric centre, determined by deiodinase 2 expression, ventrally juxtaposed to the migrating eye in sole (Solea senegalensis) correlates with asymmetric cranial ossification that in turn drives eye migration. Besides skin pigmentation that is asymmetric between dorsal and ventral sides, only the most anterior head region delimited by the eyes becomes asymmetric whereas the remainder of the head and organs therein stay symmetric. Sub-ocular ossification is common to all flatfish analysed to date, so we propose that this newly discovered mechanism is universal and is associated with eye migration in all flatfish.