Light input and the reversal of functional lateralization in the chicken brain

The impact of early-life conditions on visual discrimination abilities in free-ranging laying hens

Conditions during incubation and rearing can greatly affect the developmental trajectory of chickens, in a positive and negative way. In this study, the effect of early-life conditions on the visual discrimination abilities of adult, free-ranging laying hens was examined. These early-life treatments entailed incubation in a 12/12h green light/dark cycle and rearing with Black soldier fly larvae (BSFL) as foraging enrichment. Through a modified pebble-floor test, 171 hens of 41 to 42 wk old, housed in mobile stables with outdoor access, were tested for their ability to discriminate between food and nonfood items (mealworms and decoy mealworms). Each hen was allowed 60 pecks during the trial, from which the overall success rate, as well as within-trial learning was investigated. The latter was accomplished by dividing the 60 pecks into 3 blocks of 20 pecks and comparing the success rate between these blocks. Due to another ongoing experiment on range use, roughly half the hens received range enrichment (mealworms) at the time of testing, so this was included as a covariate in the analysis. Incubation with green light did not have an effect on the visual discrimination abilities of adult laying hens. Rearing with BSFL did have a limited beneficial effect on the visual discrimination abilities, as evidenced by a higher success rate during the first block of the visual discrimination trial. These enhanced visual discrimination abilities might be useful in a more complex free-range setting, where the animals have more foraging opportunities. Hens that received range enrichment at the time of testing, also had a higher success rate during the visual discrimination test, though they had a lower degree of test completion, likely due to habituation to the mealworms as an enrichment. The positive effects of BSFL during rearing and mealworms during the laying period stress the importance of enrichment throughout the life of the hens.

Responses in the left and right entopallium are differently affected by light stimulation in embryo

Sensory stimulation during the prenatal period has been argued to be a main factor in establishing asymmetry in the vertebrate brain. However, though largely studied in behavior and neuroanatomy, nothing is known on the effects of light stimulation in embryo on the activities of single neurons. We performed single-unit recordings from the left and right entopallium of dark- and light-incubated chicks, following ipsi-, contra-, and bilateral visual stimulation. Light incubation increased the general responsiveness of visual neurons in both the left and the right entopallium. Entopallial responses were clearly lateralized in dark-incubated chicks, which showed a general right-hemispheric dominance. This could be suppressed or inverted after light incubation, revealing the presence of both spontaneous and light-dependent asymmetries. These results suggest that asymmetry in single-neuron activity is present at the onset and can be modulated by environmental stimuli such as light exposure in embryos.

Hemispheric dominance in HVC is experience-dependent in juvenile male zebra finches

Juvenile male zebra finches (Taeniopygia guttata) must be exposed to an adult tutor during a sensitive period to develop normal adult song. The pre-motor nucleus HVC (acronym used as a proper name), plays a critical role in song learning and production (cf. Broca's area in humans). In the human brain, left-side hemispheric dominance in some language regions is positively correlated with proficiency in linguistic skills. However, it is unclear whether this pattern depends upon language learning, develops with normal maturation of the brain, or is the result of pre-existing functional asymmetries. In juvenile zebra finches, even though both left and right HVC contribute to song production, baseline molecular activity in HVC is left-dominant. To test if HVC exhibits hemispheric dominance prior to song learning, we raised juvenile males in isolation from adult song and measured neuronal activity in the left and right HVC upon first exposure to an auditory stimulus. Activity in the HVC was measured using the immediate early gene (IEG) zenk (acronym for zif-268, egr-1, NGFI-a, and krox-24) as a marker for neuronal activity. We found that neuronal activity in the HVC of juvenile male zebra finches is not lateralized when raised in the absence of adult song, while normally-reared juvenile birds are left-dominant. These findings show that there is no pre-existing asymmetry in the HVC prior to song exposure, suggesting that lateralization of the song system depends on learning through early exposure to adult song and subsequent song-imitation practice.

The effect of light during embryonic development on laterality and exploration in Western Rainbowfish

Several factors affect the development of lateralization such as hormones and light exposure during early development. Laterality also often correlates with other behavioral traits. To examine whether there is a common mechanism underlying the development of laterality and other behaviors, we manipulated laterality by exposing embryos of the Western rainbowfish (Melatotaenia australis) to light or continuous darkness during early development and determined whether a shift in laterality was associated with a change in behavior in a novel environment test at two different ages. We found that exposing eggs to darkness led to offspring that displayed significantly less lateralized behavior in the mirror test two weeks after hatching than offspring from eggs exposed to light. Interestingly, the effects of rearing condition were lost by 3 months of age. These data suggest that exposure to light can influence laterality very early in development, but such bias can be overwritten by developmental processes post-hatch. Moreover, our manipulation of laterality apparently had no influence on exploration suggesting independent causal mechanisms. The experimental manipulation of light exposure during development could be a useful tool for enhancing individuals with a specific laterality and behavioral traits to aid future research into the causes and consequences of laterality.

Novel sound exposure drives dynamic changes in auditory lateralization that are associated with perceptual learning in zebra finches

Songbirds provide a model for adult plasticity in the auditory cortex as a function of recent experience due to parallels with human auditory processing. As for speech processing in humans, activity in songbirds' higher auditory cortex (caudomedial nidopallium, NCM) is lateralized for complex vocalization sounds. However, in Zebra finches exposed to a novel heterospecific (canary) acoustic environment for 4-9 days, the typical pattern of right-lateralization is reversed. We now report that, in birds passively exposed to a novel heterospecific environment for extended periods (up to 21 days), the right-lateralized pattern of epidural auditory potentials first reverses transiently then returns to the typical pattern. Using acute, bilateral multi-unit electrophysiology, we confirm that this dynamic pattern occurs in NCM. Furthermore, extended exposure enhances discrimination for heterospecific stimuli. We conclude that lateralization is functionally labile and, when engaged by novel sensory experience, contributes to discrimination of novel stimuli that may be ethologically relevant. Future studies seek to determine whether, (1) the dynamicity of lateralized processes engaged by novel sensory experiences recurs with every novel challenge in the same organism; (2) the dynamic pattern extends to other cortical, thalamic or midbrain structures; and (3) the phenomenon generalizes across sensory modalities.

The effect of androgen exposure on cerebral lateralization in the American alligator (Alligator mississippiensis)

The division of the brain manifests in lateralized physical behaviors, where specific tasks originate from one side of the body. Previous studies have shown that birds and reptiles mediate aggression in their right hemisphere and focus on opponents with their left eye. Degree of lateralization varies between sexes, likely due to androgen inhibition of lateralization in mammals, birds, and fish, but remains untested in herpetofauna. In this experiment, we investigated the effect of androgen exposure on cerebral lateralization in the American Alligator, Alligator mississippiensis. Alligator eggs were collected and incubated at female producing temperature with a subset dosed with methyltestosterone in ovo. Dosed hatchlings were randomly paired with control individuals and their interactions were recorded. The number of bites initiated by focus from each eye and the number of times an animal was bitten on each side of the body was recorded for each individual to elucidate cerebral lateralization in aggression. Control alligators had a significant bias towards left-eye bite initiation whereas androgen exposed alligators used both eyes indiscriminately. No significance was found in injury patterns. This study suggests that androgen exposure inhibits cerebral lateralization in alligator brains and corroborates right-hemisphere mediation of aggression, something previously unstudied in crocodilians.

Ecdysone signaling determines lateral polarity and remodels neurites to form Drosophila's left-right brain asymmetry

Left-right (LR) asymmetry of the brain is fundamental to its higher-order functions. The Drosophila brain's asymmetrical body (AB) consists of a structural pair arborized from AB neurons and is larger on the right side than the left. We find that the AB initially forms LR symmetrically and then develops LR asymmetrically by neurite remodeling that is specific to the left AB and is dynamin dependent. Additionally, neuronal ecdysone signaling inhibition randomizes AB laterality, suggesting that ecdysone signaling determines AB's LR polarity. Given that AB's LR asymmetry relates to memory formation, our research establishes AB as a valuable model for studying LR asymmetry and higher-order brain function relationships.

Unfolding a sequence of sensory influences and interactions in the development of functional brain laterality

Evidence of sensory experience influencing the development of lateralized brain and behavior is reviewed. The epigenetic role of light exposure during two specific stages of embryonic development of precocial avian species is a particular focus of the research discussed. Two specific periods of light sensitivity (in early versus late incubation), each depending on different subcellular and cellular processes, affect lateralized behavior after hatching. Auditory and olfactory stimulation during embryonic development is also discussed with consideration of interactions with light-generated visual lateralization.

Light-induced asymmetries in embryonic retinal gene expression are mediated by the vascular system and extracellular matrix

Left–right asymmetries in the nervous system (lateralisation) influence a broad range of behaviours, from social responses to navigation and language. The role and pathways of endogenous and environmental mechanisms in the ontogeny of lateralisation remains to be established. The domestic chick is a model of both endogenous and experience-induced lateralisation driven by light exposure. Following the endogenous rightward rotation of the embryo, the asymmetrical position in the egg results in a greater exposure of the right eye to environmental light. To identify the genetic pathways activated by asymmetric light stimulation, and their time course, we exposed embryos to different light regimes: darkness, 6 h of light and 24 h of light. We used RNA-seq to compare gene expression in the right and left retinas and telencephalon. We detected differential gene expression in right vs left retina after 6 h of light exposure. This difference was absent in the darkness condition and had already disappeared by 24 h of light exposure, suggesting that light-induced activation is a self-terminating phenomenon. This transient effect of light exposure was associated with a downregulation of the sensitive-period mediator gene DIO2 (iodothyronine deiodinase 2) in the right retina. No differences between genes expressed in the right vs. left telencephalon were detected. Gene networks associated with lateralisation were connected to vascularisation, cell motility, and the extracellular matrix. Interestingly, we know that the extracellular matrix—including the differentially expressed PDGFRB gene—is involved in morphogenesis, sensitive periods, and in the endogenous chiral mechanism of primary cilia, that drives lateralisation. Our data show a similarity between endogenous and experience-driven lateralisation, identifying functional gene networks that affect lateralisation in a specific time window.

Activation of the Nucleus Taeniae of the Amygdala by Umami Taste in Domestic Chicks (Gallus gallus)

In chickens, the sense of taste plays an important role in detecting nutrients and choosing feed. The molecular mechanisms underlying the taste-sensing system of chickens are well studied, but the neural mechanisms underlying taste reactivity have received less attention. Here we report the short-term taste behaviour of chickens towards umami and bitter (quinine) taste solutions and the associated neural activity in the nucleus taeniae of the amygdala, nucleus accumbens and lateral septum. We found that chickens had more contact with and drank greater volumes of umami than bitter or a water control, and that chicks displayed increased head shaking in response to bitter compared to the other tastes. We found that there was a higher neural activity, measured as c-Fos activation, in response to umami taste in the right hemisphere of the nucleus taeniae of the amygdala. In the left hemisphere, there was a higher c-Fos activation of the nucleus taeniae of the amygdala in response to bitter than in the right hemisphere. Our findings provide clear evidence that chickens respond differently to umami and bitter tastes, that there is a lateralised response to tastes at the neural level, and reveals a new function of the avian nucleus taeniae of the amygdala as a region processing reward information.

It Is Not Just in the Genes

Asymmetries in the functional and structural organization of the nervous system are widespread in the animal kingdom and especially characterize the human brain. Although there is little doubt that asymmetries arise through genetic and nongenetic factors, an overarching model to explain the development of functional lateralization patterns is still lacking. Current genetic psychology collects data on genes relevant to brain lateralizations, while animal research provides information on the cellular mechanisms mediating the effects of not only genetic but also environmental factors. This review combines data from human and animal research (especially on birds) and outlines a multi-level model for asymmetry formation. The relative impact of genetic and nongenetic factors varies between different developmental phases and neuronal structures. The basic lateralized organization of a brain is already established through genetically controlled embryonic events. During ongoing development, hemispheric specialization increases for specific functions and subsystems interact to shape the final functional organization of a brain. In particular, these developmental steps are influenced by environmental experiences, which regulate the fine-tuning of neural networks via processes that are referred to as ontogenetic plasticity. The plastic potential of the nervous system could be decisive for the evolutionary success of lateralized brains.

Long-Wavelength-Filtered Light Transiently Inhibits Negative Lens-Induced Axial Eye Growth in the Chick Myopia Model

Purpose

Eye growth and myopia development in chicks, and some other animal models, can be suppressed by rearing under near-monochromatic, short-wavelength blue light. We aimed to determine whether similar effects could be achieved using glass filters that transmit a broader range of short and middle wavelengths.

Methods

On day 6 or 7 post-hatch, 169 chicks were assigned to one of three monocular lens conditions (−10 D, +10 D, plano) and reared for 7 or 10 days under one of four 201-lux lighting conditions: (1) B410 long-wavelength–filtered light, (2) B460 long-wavelength–filtered light, (3) Y48 short-wavelength–filtered light, or (4) HA50 broadband light.

Results

At 7 days, B410 (but not B460) long-wavelength–filtered light had significantly inhibited negative lens induced axial growth relative to Y48 short-wavelength–filtered light (mean difference in experimental eye = −0.249 mm; P = 0.006) and HA50 broadband light (mean difference = −0.139 mm; P = 0.038). B410 filters also inhibited the negative lens-induced increase in vitreous chamber depth relative to all other filter conditions. Corresponding changes in refraction did not occur, and biometric measurements in a separate cohort of chicks suggested that the axial dimension changes were transient and not maintained at 10 days.

Conclusions

Chromatic effects on eye growth can be achieved using filters that transmit a broad range of wavelengths even in the presence of strong cues for myopia development.

Translational Relevance

Broad-wavelength filters that provide a more “naturalistic” visual experience relative to monochromatic light have potential to alter myopia development, although the effects shown here were modest and transient and require exploration in further species.

Prenatal and Early Postnatal Behavioural Programming in Laying Hens, With Possible Implications for the Development of Injurious Pecking

Injurious pecking (IP) represents a serious concern for the welfare of laying hens (Gallus gallus domesticus). The risk of IP among hens with intact beaks in cage-free housing prompts a need for solutions based on an understanding of underlying mechanisms. In this review, we explore how behavioural programming via prenatal and early postnatal environmental conditions could influence the development of IP in laying hens. The possible roles of early life adversity and mismatch between early life programming and subsequent environmental conditions are considered. We review the role of maternal stress, egg conditions, incubation settings (temperature, light, sound, odour) and chick brooding conditions on behavioural programming that could be linked to IP. Brain and behavioural development can be programmed by prenatal and postnatal environmental conditions, which if suboptimal could lead to a tendency to develop IP later in life, as we illustrate with a Jenga tower that could fall over if not built solidly. If so, steps taken to optimise the environmental conditions of previous generations and incubation conditions, reduce stress around hatching, and guide the early learning of chicks will aid in prevention of IP in commercial laying hen flocks.

Brain Lateralization and Cognitive Capacity

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

Light-incubation effects on lateralisation of single unit responses in the visual Wulst of domestic chicks

Since the ground-breaking discovery that in-egg light exposure triggers the emergence of visual lateralisation, domestic chicks became a crucial model for research on the interaction of environmental and genetic influences for brain development. In domestic chick embryos, light exposure induces neuroanatomical asymmetries in the strength of visual projections from the thalamus to the visual Wulst. Consequently, the right visual Wulst receives more bilateral information from the two eyes than the left one. How this impacts visual Wulst's physiology is still unknown. This paper investigates the visual response properties of neurons in the left and right Wulst of dark- and light-incubated chicks, studying the effect of light incubation on bilaterally responsive cells that integrate information from both eyes. We recorded from a large number of visually responsive units, providing the first direct evidence of lateralisation in the neural response properties of units of the visual Wulst. While we confirm that some forms of lateralisation are induced by embryonic light exposure, we found also many cases of light-independent asymmetries. Moreover, we found a strong effect of in-egg light exposure on the general development of the functional properties of units in the two hemispheres. This indicates that the effect of embryonic stimulation goes beyond its contribution to the emergence of some forms of lateralisation, with influences on the maturation of visual units in both hemispheres.

Sensitive periods for social development: Interactions between predisposed and learned mechanisms

We analysed research that makes use of precocial species as animal models to describe the interaction of predisposed mechanisms and environmental factors in early learning, in particular for the development of social cognition. We also highlight the role of sensitive periods in this interaction, focusing on domestic chicks as one of the main animal models for this field. In the first section of the review, we focus on the emergence of early predispositions to attend to social partners. These attentional biases appear before any learning experience about social stimuli. However, non-specific experiences occurring during sensitive periods of the early post-natal life determine the emergence of these predisposed mechanisms for the detection of social partners. Social predispositions have an important role for the development learning-based social cognitive functions, showing the interdependence of predisposed and learned mechanisms in shaping social development. In the second part of the review we concentrate on the reciprocal interactions between filial imprinting and spontaneous (not learned) social predispositions. Reciprocal influences between these two sets of mechanisms ensure that, in the natural environment, filial imprinting will target appropriate social objects. Neural and physiological mechanisms regulating the sensitive periods for the emergence of social predispositions and for filial imprinting learning are also described.

Brain Lateralization: A Comparative Perspective

Comparative studies on brain asymmetry date back to the 19th century but then largely disappeared due to the assumption that lateralization is uniquely human. Since the reemergence of this field in the 1970s, we learned that left-right differences of brain and behavior exist throughout the animal kingdom and pay off in terms of sensory, cognitive, and motor efficiency. Ontogenetically, lateralization starts in many species with asymmetrical expression patterns of genes within the Nodal cascade that set up the scene for later complex interactions of genetic, environmental, and epigenetic factors. These take effect during different time points of ontogeny and create asymmetries of neural networks in diverse species. As a result, depending on task demands, left- or right-hemispheric loops of feedforward or feedback projections are then activated and can temporarily dominate a neural process. In addition, asymmetries of commissural transfer can shape lateralized processes in each hemisphere. It is still unclear if interhemispheric interactions depend on an inhibition/excitation dichotomy or instead adjust the contralateral temporal neural structure to delay the other hemisphere or synchronize with it during joint action. As outlined in our review, novel animal models and approaches could be established in the last decades, and they already produced a substantial increase of knowledge. Since there is practically no realm of human perception, cognition, emotion, or action that is not affected by our lateralized neural organization, insights from these comparative studies are crucial to understand the functions and pathologies of our asymmetric brain.

Prenatal Visual Exposure to a Predator Influences Lateralization in Goldbelly Topminnows

The role of genetic and environmental factors in modulating the development of brain lateralization is far from being fully understood, and the presence of individual differences in several lateralized functions is still an open question. In goldbelly topminnows, the genetic basis of asymmetrical functions in the brain has been studied, and recently it has been found that light stimulation influences the expression of lateralization of newborns. Here, we investigated whether prenatal exposure to predators affects the development of lateralization in 10-day-old topminnows born from females exposed to a real or to a simulated predator during pregnancy. Offspring from females exposed to a real predator were lateralized in both visual and motor tests, whereas fish from females exposed to a simulated predator were not and did not differ from controls. Prenatal exposure to a real predator might promote the alignment of lateralization in the same direction in different individuals.

Light-dependent development of the tectorotundal projection in pigeons

Left-right differences in the structural and functional organization of the brain are widespread in the animal kingdom and develop in close gene-environment interactions. The visual system of birds like chicks and pigeons exemplifies how sensory experience shapes lateralized visual processing. Owing to an asymmetrical posture of the embryo in the egg, the right eye/ left brain side is more strongly light-stimulated what triggers asymmetrical differentiation processes leading to a left-hemispheric dominance for visuomotor control. In pigeons (Columba livia), a critical neuroanatomical element is the asymmetrically organized tectofugal pathway. Here, more fibres cross from the right tectum to the left rotundus than vice versa. In the current study, we tested whether the emergence of this projection asymmetry depends on embryonic light stimulation by tracing tectorotundal neurons in pigeons with and without lateralized embryonic light experience. The quantitative tracing pattern confirmed higher bilateral innervation of the left rotundus in light-exposed and thus, asymmetrically light-stimulated pigeons. This was the same in light-deprived pigeons. Here, however, also the right rotundus received an equally strong bilateral input. This suggests that embryonic light stimulation does not increase bilateral tectal innervation of the stronger stimulated left but rather decreases such an input pattern to the right brain side. Combined with a morphometric analysis, our data indicate that embryonic photic stimulation specifically affects differentiation of the contralateral cell population. Differential modification of ipsi- and contralateral tectorotundal connections could have important impact on the regulation of intra- and interhemispheric information transfer and ultimately on hemispheric dominance pattern during visual processing.

Asymmetry of Motor Behavior and Sensory Perception: Which Comes First?

By examining the development of lateralization in the sensory and motor systems of the human fetus and chick embryo, this paper debates which lateralized functions develop first and what interactions may occur between the different sensory and motor systems during development. It also discusses some known influences of inputs from the environment on the development of lateralization, particularly the effects of light exposure on the development of visual and motor lateralization in chicks. The effects of light on the human fetus are related in this context. Using the chick embryo as a model to elucidate the genetic and environmental factors involved in development of lateralization, some understanding has been gained about how these lateralized functions emerge. At the same time, the value of carrying out much more research on the development of the various types of lateralization has become apparent.

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.

Molecular and cellular determinants of motor asymmetry in zebrafish

Asymmetries in motor behavior, such as human hand preference, are observed throughout bilateria. However, neural substrates and developmental signaling pathways that impose underlying functional lateralization on a broadly symmetric nervous system are unknown. Here we report that in the absence of over-riding visual information, zebrafish larvae show intrinsic lateralized motor behavior that is mediated by a cluster of 60 posterior tuberculum (PT) neurons in the forebrain. PT neurons impose motor bias via a projection through the habenular commissure. Acquisition of left/right identity is disrupted by heterozygous mutations in mosaic eyes and mindbomb, genes that regulate Notch signaling. These results define the neuronal substrate for motor asymmetry in a vertebrate and support the idea that haploinsufficiency for genes in a core developmental pathway destabilizes left/right identity.

Many animals show individual left/right biases in motor behaviour, but underlying neural substrates have proven elusive. Here the authors describe neurons that maintain individual, context-dependent lateralisation of swimming behaviour in zebrafish.

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.

Prenatal light exposure influences gait performance and body composition in bobwhite quail chicks

Maternal nesting behavior, which includes periods of patterned inattention, provides key elements essential for avian embryonic development, including regulation of temperature and light. For example, avian research consistently shows the importance of prenatal light exposure for several developmental processes; however, this research has primarily focused on artificial light regimens (i.e. 24 hr, 0 hr light). Comparatively less is known about how exposure to naturally occurring light patterns during incubation influence motor performance, body composition (i.e. body mass, bone length), and developmental age (incubation length). Here we conducted two experiments which investigated the effects of prenatal light exposure on developmental age, body composition, and gait performance in 1-day-old bobwhite quail. Experiment 1 investigated crepuscular light exposure during the last two days of incubation under two light duration treatments (2 hr & 6 hr) compared to a 12 hr continuous light schedule. Results indicated crepuscular prenatal light experience extended the incubation period for 2 hr exposed embryos, but not for 6 hr exposed embryos and negatively influenced postnatal body composition and postnatal gait performance when compared to 12 hr continuous light embryos. Experiment 2 examined the influence of prenatal light duration (2 hr vs 6 hr) and light presentation (crepuscular vs sporadic). Results demonstrated sporadic light presentation improved gait performance in 2 hr exposed hatchlings, but not 6 hr exposed hatchlings, improved body composition in 6 hr exposed hatchlings, but not 2 hr exposed hatchlings, and did not alter incubation length when compared to crepuscular light counterparts. This study provides further evidence for the importance of maternally regulated sensory stimulation during the prenatal period on early postnatal motor development.

Does Functional Lateralization in Birds Have any Implications for Their Welfare?

We know a good deal about brain lateralization in birds and a good deal about animal welfare, but relatively little about whether there is a noteworthy relationship between avian welfare and brain lateralization. In birds, the left hemisphere is specialised to categorise stimuli and to discriminate preferred categories from distracting stimuli (e.g., food from an array of inedible objects), whereas the right hemisphere responds to small differences between stimuli, controls social behaviour, detects predators and controls attack, fear and escape responses. In this paper, we concentrate on visual lateralization and the effect of light exposure of the avian embryo on the development of lateralization, and we consider its role in the welfare of birds after hatching. Findings suggest that light-exposure during incubation has a general positive effect on post-hatching behaviour, likely because it facilitates control of behaviour by the left hemisphere, which can suppress fear and other distress behaviour controlled by the right hemisphere. In this context, particular attention needs to be paid to the influence of corticosterone, a stress hormone, on lateralization. Welfare of animals in captivity, as is well known, has two cornerstones: enrichment and reduction of stress. What is less well-known is the link between the influence of experience on brain lateralization and its consequent positive or negative outcomes on behaviour. We conclude that the welfare of birds may be diminished by failure to expose the developing embryos to light but we also recognise that more research on the association between lateralization and welfare is needed.

Evolution of cerebral asymmetry

The human brain is often characterized in terms of a duality, with the left and right brains serving complementary functions, and even individuals are sometimes classified as either "left-brained" or "right-brained." Recent evidence from brain imaging shows that hemispheric asymmetry is multidimensional, comprised of independent lateralized circuits. Cerebral asymmetries, which include handedness, probably arise in phylogenesis through the fissioning of ancestral systems that divided and lateralized with increasing demand for specialization. They also vary between individuals, with some showing absent or reversed asymmetries. It is unlikely that this variation is controlled by a single gene, as sometimes assumed, but depends rather on complex interplay among several, perhaps many, genes. Hemispheric asymmetry has often been regarded as a unique mark of being human, but it has also become evident that behavioral and cerebral asymmetries are not confined to humans, and are widespread among animal species. They nevertheless exist against a fundamental background of bilateral symmetry, suggesting a tradeoff between the two. Individual differences in asymmetry, moreover, are themselves adaptive, contributing to the cognitive and behavioral specializations necessary for societies to operate efficiently.

Spontaneous and light-induced lateralization of immediate early genes expression in domestic chicks

Exposure of domestic chicks' eggs to light during embryo incubation stimulates asymmetrically the two eye-systems, reaching selectively the right eye (left hemisphere) and inducing asymmetries at the behavioral and neural level. Surprisingly, though, some types of lateralization have been observed also in dark incubated chicks, especially at the behavioral level. Here we investigate the mechanisms subtending the development of lateralization, in the presence and in the absence of embryonic light exposure. We measured the baseline level of expression for the immediate early gene product c-Fos, used as an indicator of the spontaneous level of neural activity and plasticity in four areas of the two hemispheres (preoptic area, septum, hippocampus and intermediate medial mesopallium). Additional DAPI staining measured overall cell density (regardless of c-Fos expression), ruling out any confound due to underlying asymmetries in cell density between the hemispheres. In different brain areas, c-Fos expression was lateralized either in light- (septum) or in dark-incubated chicks (preoptic area). Light exposure increased c-Fos expression in the left hemisphere, suggesting that c-Fos expression could participate to the known effects of light stimulation on brain asymmetries. Interestingly, this effect was visible few days after the end of the light exposure, revealing a delayed effect of light exposure on c-Fos baseline expression in brain areas outside the visual pathways. In the preoptic area of dark incubated chicks, we found a rightward bias for c-Fos expression, revealing that lateralization of the baseline level of activity and plasticity is present in the developing brain also in the absence of light exposure.

A review of environmental enrichment for laying hens during rearing in relation to their behavioral and physiological development

Globally, laying hen production systems are a focus of concern for animal welfare. Recently, the impacts of rearing environments have attracted attention, particularly with the trend toward more complex production systems including aviaries, furnished cages, barn, and free-range. Enriching the rearing environments with physical, sensory, and stimulatory additions can optimize the bird's development but commercial-scale research is limited. In this review, "enrichment" is defined as anything additional added to the bird's environment including structurally complex rearing systems. The impacts of enrichments on visual development, neurobehavioral development, auditory stimulation, skeletal development, immune function, behavioral development of fear and pecking, and specifically pullets destined for free-range systems are summarized and areas for future research identified. Visual enrichment and auditory stimulation may enhance neural development but specific mechanisms of impact and suitable commercial enrichments still need elucidating. Enrichments that target left/right brain hemispheres/behavioral traits may prepare birds for specific types of adult housing environments (caged, indoor, outdoor). Similarly, structural enrichments are needed to optimize skeletal development depending on the adult layer system, but specific physiological processes resulting from different types of exercise are poorly understood. Stimulating appropriate pecking behavior from hatch is critical but producers will need to adapt to different flock preferences to provide enrichments that are utilized by each rearing group. Enrichments have potential to enhance immune function through the application of mild stressors that promote adaptability, and this same principle applies to free-range pullets destined for variable outdoor environments. Complex rearing systems may have multiple benefits, including reducing fear, that improve the transition to the layer facility. Overall, there is a need to commercially validate positive impacts of cost-effective enrichments on bird behavior and physiology.

Short term optical defocus perturbs normal developmental shifts in retina/RPE protein abundance

BACKGROUND

Myopia (short-sightedness) affects approximately 1.4 billion people worldwide, and prevalence is increasing. Animal models induced by defocusing lenses show striking similarity with human myopia in terms of morphology and the implicated genetic pathways. Less is known about proteome changes in animals. Thus, the present study aimed to improve understanding of protein pathway responses to lens defocus, with an emphasis on relating expression changes to no lens control development and identifying bidirectional and/or distinct pathways across myopia and hyperopia (long-sightedness) models.

RESULTS

Quantitative label-free proteomics and gene set enrichment analysis (GSEA) were used to examine protein pathway expression in the retina/RPE of chicks following 6 h and 48 h of myopia induction with - 10 dioptre (D) lenses, hyperopia induction with +10D lenses, or normal no lens rearing. Seventy-one pathways linked to cell development and neuronal maturation were differentially enriched between 6 and 48 h in no lens chicks. The majority of these normal developmental changes were disrupted by lens-wear (47 of 71 pathways), however, only 11 pathways displayed distinct expression profiles across the lens conditions. Most notably, negative lens-wear induced up-regulation of proteins involved in ATP-driven ion transport, calcium homeostasis, and GABA signalling between 6 and 48 h, while the same proteins were down-regulated over time in normally developing chicks. Glutamate and bicarbonate/chloride transporters were also down-regulated over time in normally developing chicks, and positive lens-wear inhibited this down-regulation.

CONCLUSIONS

The chick retina/RPE proteome undergoes extensive pathway expression shifts during normal development. Most of these pathways are further disrupted by lens-wear. The identified expression patterns suggest close interactions between neurotransmission (as exemplified by increased GABA receptor and synaptic protein expression), cellular ion homeostasis, and associated energy resources during myopia induction. We have also provided novel evidence for changes to SLC-mediated transmembrane transport during hyperopia induction, with potential implications for signalling at the photoreceptor-bipolar synapse. These findings reflect a key role for perturbed neurotransmission and ionic homeostasis in optically-induced refractive errors, and are predicted by our Retinal Ion Driven Efflux (RIDE) model.

Effect of yolk corticosterone on begging in the yellow-legged gull

Behavioral lateralization is widespread across vertebrates. The development of lateralization is affected by both genetic and environmental factors. In birds, maternal substances in the egg can affect offspring lateralization via activational and/or organizational effects. Corticosterone affects the development of brain asymmetry, suggesting that variation in yolk corticosterone concentration may also influence post-natal behavioral lateralization, a hypothesis that has never been tested so far. In the yellow-legged gull (Larus michahellis), we increased yolk corticosterone concentration within physiological limits and analyzed the direction of lateralization of hatchlings in reverting from supine to prone position ('RTP' response) and in pecking at dummy parental bills to solicit food provisioning ('begging' response). We found that corticosterone treatment negatively affected the frequency of begging and it may cause a slight leftward lateralization. However, the direction of lateralization of the RTP response was not affected by corticosterone administration. Thus, our study shows a maternal effect mediated by corticosterone on a behavioral trait involved in parent-offspring communication during food provisioning events. The findings on lateralization are not conclusive due to the weak effect size but provide information for further ecological and evolutionary studies, investigating mechanisms underlying the development of lateralization.

Visuospatial attention in the lateralised brain of pigeons - a matter of ontogenetic light experiences

The ontogenetic mechanisms leading to complementary hemispheric specialisations of the two brain halves are poorly understood. In pigeons, asymmetrical light stimulation during development triggers the left-hemispheric dominance for visuomotor control but light effects on right-hemispheric specialisations are largely unknown. We therefore tested adult pigeons with and without embryonic light experience in a visual search task in which the birds pecked peas regularly scattered on an area in front of them. Comparing the pecking pattern of both groups indicates that the embryonic light conditions differentially influence biased visuospatial attention under mono- and binocular seeing conditions. When one eye was occluded, dark-incubated pigeons peck only within the limits of the visual hemifield of the seeing eye. Light-exposed pigeons also peck into the contralateral field indicating enlarged monocular visual fields of both hemispheres. While dark-incubated birds evinced an attentional bias to the right halfspace when seeing with both eyes, embryonic light exposure shifted this to the left. Thus, embryonic light experience modifies processes regulating biased visuospatial attention of the adult birds depending on the seeing conditions during testing. These data support the impact of light onto the emergence of functional dominances in both hemispheres and point to the critical role of interhemispheric processes.

The Human Fetus Preferentially Engages with Face-like Visual Stimuli

In the third trimester of pregnancy, the human fetus has the capacity to process perceptual information [1-3]. With advances in 4D ultrasound technology, detailed assessment of fetal behavior [4] is now possible. Furthermore, modeling of intrauterine conditions has indicated a substantially greater luminance within the uterus than previously thought [5]. Consequently, light conveying perceptual content could be projected through the uterine wall and perceived by the fetus, dependent on how light interfaces with maternal tissue. We do know that human infants at birth show a preference to engage with a top-heavy, face-like stimulus when contrasted with all other forms of stimuli [6, 7]. However, the viability of performing such an experiment based on visual stimuli projected through the uterine wall with fetal participants is not currently known. We examined fetal head turns to visually presented upright and inverted face-like stimuli. Here we show that the fetus in the third trimester of pregnancy is more likely to engage with upright configural stimuli when contrasted to inverted visual stimuli, in a manner similar to results with newborn participants. The current study suggests that postnatal experience is not required for this preference. In addition, we describe a new method whereby it is possible to deliver specific visual stimuli to the fetus. This new technique provides an important new pathway for the assessment of prenatal visual perceptual capacities.

Coordinated movement is influenced by prenatal light experience in bobwhite quail chicks (Colinus virginianus)

Sensory-motor development begins early during embryogenesis and is influenced by sensory experience. Little is known about the prenatal factors that influence the development of motor coordination. Here we investigated whether and to what extent prenatal light experience can influence the development of motor coordination in bobwhite quail hatchlings. Quail embryos were incubated under four light conditions: no light (dark), 2h of total light (2HR), 6h of total light (6HR), and diffused sunlight (controls). Hatchlings were video recording walking down a runway at three developmental ages (12, 24, and 48h). Videos were assessed for forward locomotion, a measurement of motor coordination, falls, a measurement of motor instability, and motivation to complete the task. We anticipated a linear decline of coordination with a reduction in prenatal light experience and improved coordination with age. Furthermore, as motor coordination becomes more laborious we anticipated motivation to complete the task would decline. However, our findings revealed hatchlings did not uniformly improve with age as expected, nor did the reduction of light result in a linear reduction in motor coordination. Instead, we found a more complex relationship with 6HR and 2HR hatchlings showing distinct patterns of stability and instability. Similarly, we found a reduction in motivation within the 6HR light condition. It appears that prenatal light exposure influences the development of postnatal motor coordination and we discuss these finding in light of neurodevelopmental processes influenced by light experience.

Lateralization of Eye Use in Cuttlefish: Opposite Direction for Anti-Predatory and Predatory Behaviors

Vertebrates with laterally placed eyes typically exhibit preferential eye use for ecological activities such as scanning for predators or prey. Processing visual information predominately through the left or right visual field has been associated with specialized function of the left and right brain. Lateralized vertebrates often share a general pattern of lateralized brain function at the population level, whereby the left hemisphere controls routine behaviors and the right hemisphere controls emergency responses. Recent studies have shown evidence of preferential eye use in some invertebrates, but whether the visual fields are predominately associated with specific ecological activities remains untested. We used the European common cuttlefish, Sepia officinalis, to investigate whether the visual field they use is the same, or different, during anti-predatory, and predatory behavior. To test for lateralization of anti-predatory behavior, individual cuttlefish were placed in a new environment with opaque walls, thereby obliging them to choose which eye to orient away from the opaque wall to scan for potential predators (i.e., vigilant scanning). To test for lateralization of predatory behavior, individual cuttlefish were placed in the apex of an isosceles triangular arena and presented with two shrimp in opposite vertexes, thus requiring the cuttlefish to choose between attacking a prey item to the left or to the right of them. Cuttlefish were significantly more likely to favor the left visual field to scan for potential predators and the right visual field for prey attack. Moreover, individual cuttlefish that were leftward directed for vigilant scanning were predominately rightward directed for prey attack. Lateralized individuals also showed faster decision-making when presented with prey simultaneously. Cuttlefish appear to have opposite directions of lateralization for anti-predatory and predatory behavior, suggesting that there is functional specialization of each optic lobe (i.e., brain structures implicated in visual processing). These results are discussed in relation to the role of lateralized brain function and the evolution of population level lateralization.