Light-dependent development of asymmetry in the ipsilateral and contralateral thalamofugal visual projections of the chick

Effects of lighted incubation and foraging enrichment during rearing on individual fear behavior, corticosterone, and neuroplasticity in laying hen pullets

Environmental conditions during incubation and rearing can influence stress responsivity of laying hen pullets throughout their lifespan, and therefore have important implications for their welfare. In this study, a 12:12h green LED light-dark cycle during incubation and larvae provisioning as enrichment during rearing were tested as strategies to optimize early-life conditions and thereby decrease stress responsivity in ISA Brown laying hens. A combination of parameters was measured to indicate neuronal, physiological, and behavioral changes that may affect fear and stress. The proteins calbindin D28k (calbindin1), doublecortin (DCX), and neuronal nuclein protein (NeuN) were quantified after hatch as a proxy for brain plasticity. Plasma and feather corticosterone levels were measured after hatch and at the end of the rearing phase, and fearfulness was investigated through a series of behavioral tests (i.e., voluntary approach, open field, tonic immobility, and manual restraint tests). No effects of light during incubation were found on calbindin1, DCX, or NeuN. Neither of the treatments affected corticosterone levels in blood plasma and feathers. Light-incubated pullets showed less fearfulness towards humans in the voluntary approach test, but not in the other behavioral tests reported in this study. Larvae provisioning had no effect on behavior. Our study showed minor effects of light during incubation and no effects of enrichment during rearing on stress responsivity of laying hen pullets. The small effects may be explained by the enriched rearing conditions for all birds in this experiment (low stocking density, natural daylight, and 24/7 classical music). Given the promising results of lighted incubation in other studies, which were mostly performed in broiler chickens, and evidence regarding the positive effects of enrichment during rearing, the potential of these strategies to improve laying hen welfare needs to be explored further.

Early-life interventions to prevent feather pecking and reduce fearfulness in laying hens

Severe feather pecking, the pulling out of feathers of conspecifics, is a major welfare issue in laying hens. Possible underlying causes are fearfulness and lack of foraging opportunities. Because early life is a crucial stage in behavioral development, adapting the incubation and rearing environment to the birds' needs may reduce fearfulness and prevent the development of feather pecking. In a 2 × 2 factorial design study, we investigated whether a green light-dark cycle throughout incubation, which resembles natural incubation circumstances more than the standard dark incubation, and foraging enrichment with live larvae during rearing reduce fearfulness and feather pecking and increase foraging behavior of laying hen pullets from an early age onwards. In this 2-batch experiment, 1,100 ISA Brown eggs were incubated under either 0 h of light/24 h of darkness or 12 h of green LED light/12 h of darkness. After hatching, 400 female chicks (200 per batch) were housed in 44 pens (8-10 chicks per pen). During the entire rearing phase (0-17 wk of age), half of the pens received black soldier fly larvae in a food puzzle as foraging enrichment. We assessed fear of novel objects and humans, feather pecking, plumage condition, foraging behavior, and recovery time after a 3-fold vaccination (acute stressor). A slight increase in the number of foraging bouts was only seen with larvae provisioning (rate ratio 1.19, 95% CI 1.02-1.29, P = 0.008). Neither lighted incubation nor larvae provisioning affected fearfulness, feather pecking, plumage condition or recovery time after vaccination. In conclusion, the present study showed no effects of light during incubation and minor effects of foraging enrichment during rearing on the behavior of laying hen pullets. Further research is recommended on other welfare aspects.

Asymmetric activity of NetrinB controls laterality of the Drosophila brain

Left-Right (LR) asymmetry of the nervous system is widespread across animals and is thought to be important for cognition and behaviour. But in contrast to visceral organ asymmetry, the genetic basis and function of brain laterality remain only poorly characterized. In this study, we performed RNAi screening to identify genes controlling brain asymmetry in Drosophila. We found that the conserved NetrinB (NetB) pathway is required for a small group of bilateral neurons to project asymmetrically into a pair of neuropils (Asymmetrical Bodies, AB) in the central brain in both sexes. While neurons project unilaterally into the right AB in wild-type flies, netB mutants show a bilateral projection phenotype and hence lose asymmetry. Developmental time course analysis reveals an initially bilateral connectivity, eventually resolving into a right asymmetrical circuit during metamorphosis, with the NetB pathway being required just prior symmetry breaking. We show using unilateral clonal analysis that netB activity is required specifically on the right side for neurons to innervate the right AB. We finally show that loss of NetB pathway activity leads to specific alteration of long-term memory, providing a functional link between asymmetrical circuitry determined by NetB and animal cognitive functions.

Simplified Attachable EEG Revealed Child Development Dependent Neurofeedback Brain Acute Activities in Comparison with Visual Numerical Discrimination Task and Resting

The development of an easy-to-attach electroencephalograph (EEG) would enable its frequent use for the assessment of neurodevelopment and clinical monitoring. In this study, we designed a two-channel EEG headband measurement device that could be used safely and was easily attachable and removable without the need for restraint or electrode paste or gel. Next, we explored the use of this device for neurofeedback applications relevant to education or neurocognitive development. We developed a prototype visual neurofeedback game in which the size of a familiar local mascot changes in the PC display depending on the user's brain wave activity. We tested this application at a local children's play event. Children at the event were invited to experience the game and, upon agreement, were provided with an explanation of the game and support in attaching the EEG device. The game began with a consecutive number visual discrimination task which was followed by an open-eye resting condition and then a neurofeedback task. Preliminary linear regression analyses by the least-squares method of the acquired EEG and age data in 30 participants from 5 to 20 years old suggested an age-dependent left brain lateralization of beta waves at the neurofeedback stage (p = 0.052) and of alpha waves at the open-eye resting stage (p = 0.044) with potential involvement of other wave bands. These results require further validation.

The commissura anterior compensates asymmetries of visual representation in pigeons

This study was undertaken to understand what is transferred between hemispheres through the commissura anterior during a colour discrimination task in pigeons. We transiently blocked neuronal activity of the arcopallium of one hemisphere to interrupt interhemispheric communication. Before and during this intervention, we recorded from arcopallial neurons of the non-anaesthetized side while the animals discriminated stimuli ipsilateral to the recorded neurons. Due to the complete crossover of optic nerves in birds, we assumed that these neurons were at least in part requiring information from the other hemisphere to properly run the task. While lidocaine injections in both hemispheres caused some performance reductions, deficits of right arcopallial neurons were much larger when blocking interhemispheric transfer. Our results make it likely that visual information is exchanged through the commissura anterior in an asymmetrical manner with the left hemisphere providing the other side more information about the right visual half-field than vice versa.

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.

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.

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.

Early-infant diagnostic predictors of the neuro-behavioral development after neonatal care

Multidimensional diagnosis plays a central role in infant developmental care, which leads to the prediction of future disabilities. Information consolidated from objective and subjective, early and late, central and peripheral data may reveal neuro-pathological mechanisms and realize earlier and more precise preventive intervention. In the current study, we retrospectively searched correlating factors to the following neurological and behavioral development of 'Head Control' and 'Roll Over' using multivariate correlation analysis of differ-ent diagnostic domains over age, subject/object information of the patients who were previously admitted in our neonatal intensive care unit (NICU) and could be developmentally followed up in our outpatient clinic. Based on the hematologic and biochemical data, MRI brain anatomy during NICU hospitalization, we characterized all the acquired data distribution from 31 infants with either 'appeared neurologically normal (ANN, n = 21)’ or 'appeared neurologically abnormal (ANA, n = 10)’ pro tempore, with a physician's clinical judgment before discharge. Besides single factor comparisons between ANN and ANA, we examined their development difference by using the multidimensional information processing, principal component analysis (PCA). The diagnostic predictors of neuro-behavioral development were selected by regression analysis with variable selection. It resulted that hematological and brain anatomical factors seemed correlated to both ‘Head Control’ and ‘Roll Over’. This report suggested certain possibility of the cross-domain translational approach between subjective and objective developmental information through multivariate analyses, with candidate markers preliminarily to be evaluated in further studies.

Functional and structural comparison of visual lateralization in birds - similar but still different

Vertebrate brains display physiological and anatomical left-right differences, which are related to hemispheric dominances for specific functions. Functional lateralizations likely rely on structural left-right differences in intra- and interhemispheric connectivity patterns that develop in tight gene-environment interactions. The visual systems of chickens and pigeons show that asymmetrical light stimulation during ontogeny induces a dominance of the left hemisphere for visuomotor control that is paralleled by projection asymmetries within the ascending visual pathways. But structural asymmetries vary essentially between both species concerning the affected pathway (thalamo- vs. tectofugal system), constancy of effects (transient vs. permanent), and the hemisphere receiving stronger bilateral input (right vs. left). These discrepancies suggest that at least two aspects of visual processes are influenced by asymmetric light stimulation: (1) visuomotor dominance develops within the ontogenetically stronger stimulated hemisphere but not necessarily in the one receiving stronger bottom-up input. As a secondary consequence of asymmetrical light experience, lateralized top-down mechanisms play a critical role in the emergence of hemispheric dominance. (2) Ontogenetic light experiences may affect the dominant use of left- and right-hemispheric strategies. Evidences from social and spatial cognition tasks indicate that chickens rely more on a right-hemispheric global strategy whereas pigeons display a dominance of the left hemisphere. Thus, behavioral asymmetries are linked to a stronger bilateral input to the right hemisphere in chickens but to the left one in pigeons. The degree of bilateral visual input may determine the dominant visual processing strategy when redundant encoding is possible. This analysis supports that environmental stimulation affects the balance between hemispheric-specific processing by lateralized interactions of bottom-up and top-down systems.

A flexion period for attachment formation in isolated chicks to unfamiliar peers visualized in a developmental trajectory space through behavioral multivariate correlation analysis

Attachment formation is crucial for social animals to survive in natural environments. Predisposition and imprinting mechanisms have been well documented as a process of con-specific affiliation development. However, it is unclear how neonatal stage attachment formation leads to juvenile peer sociality. Here we have developed an animal model (Gallus gallus domesticus) and a method of quantitative behavioral analysis, to study the developmental trajectory from postnatal day (P) 3 through to P21. Domestic chicks were raised in either group or isolated conditions and we focused on social behavior during a two-minute meeting context with unfamiliar group peers at P3, 7, 13, 16, and 21. Results showed that relative to isolated chicks, group reared chicks were more active behaviorally, when facing peers at P3 and that this activity declined slightly over development, up to P13. Isolated chicks that had not met any animals except humans, exhibited a major change in social behavior around P7, in particular, with increasing activity (head moving velocity and rotation velocity) and distress calls. This modulation disappeared after P13, suggesting the existence of a sensitive window for behavior toward peers around P7. These findings in isolated chicks suggest the maturation of new neuronal substrates for peer-social emotion and cognition, resulting in a new combination of behavioral modules.

Asymmetry of different brain structures in homing pigeons with and without navigational experience

Homing pigeons (Columba livia f.d.) are well-known for their homing abilities, and their brains seem to be functionally adapted to homing as exemplified, e.g. by their larger hippocampi and olfactory bulbs. Their hippocampus size is influenced by navigational experience, and, as in other birds, functional specialisation of the left and right hemispheres (‘lateralisation’) occurs in homing pigeons. To show in what way lateralisation is reflected in brain structure volume, and whether some lateralisation or asymmetry in homing pigeons is caused by experience, we compared brains of homing pigeons with and without navigational experience referring to this. Fourteen homing pigeons were raised under identical constraints. After fledging, seven of them were allowed to fly around the loft and participated successfully in races. The other seven stayed permanently in the loft and thus did not share the navigational experiences of the first group. After reaching sexual maturity, all individuals were killed and morphometric analyses were carried out to measure the volumes of five basic brain parts and eight telencephalic brain parts. Measurements of telencephalic brain parts and optic tectum were done separately for the left and right hemispheres. The comparison of left/right quotients of both groups reveal that pigeons with navigational experience show a smaller left mesopallium in comparison with the right mesopallium and pigeons without navigational experience a larger left mesopallium in comparison with the right one. Additionally, there are significant differences between left and right brain subdivisions within the two pigeon groups, namely a larger left hyperpallium apicale in both pigeon groups and a larger right nidopallium, left hippocampus and right optic tectum in pigeons with navigational experience. Pigeons without navigational experience did not show more significant differences between their left and right brain subdivisions. The results of our study confirm that the brain of homing pigeons is an example for mosaic evolution and indicates that lateralisation is correlated with individual life history (experience) and not exclusively based on heritable traits.

Lateralization of social cognition in the domestic chicken (Gallus gallus)

In this paper, we report on the ongoing work in our laboratories on the effect of lateralization produced by light exposure in the egg on social cognition in the domestic chick (Gallus gallus). The domestic chick possesses a lateralized visual system. This has effects on the chick's perception towards and interaction with its environment. This includes its ability to live successfully within a social group. We show that there is a tendency for right brain hemisphere dominance when performing social cognitive actions. As such, chicks show a left hemispatial bias for approaching a signalled target object, tend to perceive gaze and faces of human-like masks more effectively when using their left eye, are able to inhibit a pecking response more effectively when viewing a neighbour tasting a bitter substance with their left eye, and are better able to perform a transitive inference task when exposed to light in the egg and when forced to use their left eye only compared to dark-hatched or right eye chicks. Some of these effects were sex specific, with male chicks tending to show an increased effect of lateralization on their behaviours. These data are discussed in terms of overall social cognition in group living.

Extrinsic embryonic sensory stimulation alters multimodal behavior and cellular activation

Embryonic vision is generated and maintained by spontaneous neuronal activation patterns, yet extrinsic stimulation also sculpts sensory development. Because the sensory and motor systems are interconnected in embryogenesis, how extrinsic sensory activation guides multimodal differentiation is an important topic. Further, it is unknown whether extrinsic stimulation experienced near sensory sensitivity onset contributes to persistent brain changes, ultimately affecting postnatal behavior. To determine the effects of extrinsic stimulation on multimodal development, we delivered auditory stimulation to bobwhite quail groups during early, middle, or late embryogenesis, and then tested postnatal behavioral responsiveness to auditory or visual cues. Auditory preference tendencies were more consistently toward the conspecific stimulus for animals stimulated during late embryogenesis. Groups stimulated during middle or late embryogenesis showed altered postnatal species-typical visual responsiveness, demonstrating a persistent multimodal effect. We also examined whether auditory-related brain regions are receptive to extrinsic input during middle embryogenesis by measuring postnatal cellular activation. Stimulated birds showed a greater number of ZENK-immunopositive cells per unit volume of brain tissue in deep optic tectum, a midbrain region strongly implicated in multimodal function. We observed similar results in the medial and caudomedial nidopallia in the telencephalon. There were no ZENK differences between groups in inferior colliculus or in caudolateral nidopallium, avian analog to prefrontal cortex. To our knowledge, these are the first results linking extrinsic stimulation delivered so early in embryogenesis to changes in postnatal multimodal behavior and cellular activation. The potential role of competitive interactions between the sensory and motor systems is discussed.

Breaking the balance: ocular BDNF-injections induce visual asymmetry in pigeons

In pigeons, asymmetric photic stimulation around hatch induces functional visual asymmetries that are accompanied by left-right differences in tectal cell sizes. Different aspects of light-dependent neuronal differentiation are known to be mediated by the brain-derived neurotrophic factor (BDNF). Therefore, we investigated by means of single or triple BDNF- or saline-injections into the right eye of dark-incubated pigeon hatchlings if ocular BDNF enrichment mimics the effects of biased visual input. As adults, the birds were tested in a grit-grain discrimination task to estimate the degree and direction of visual lateralization followed by a morphometric analysis of retinal and tectal cells. The grit-grain discrimination task demonstrated that triple BDNF-injections enhanced visuoperceptual and visuomotor functioning of the left eye system. Morphometric analysis showed bilateral cell-type dependent effects within the optic tectum. While single-BDNF injections increased cell body sizes of calbindin-positive efferent neurons, triple-injections decreased cell sizes of parvalbumin-positive cells. Moreover, single BDNF-injections increased retinal cell sizes within the contralateral eye. Analysis of BDNF-induced intracellular signaling demonstrated enhanced downstream Ras activation for at least 24 h within both tectal halves whereas activity changes within the contralateral retina could not be detected. This points to primarily tectal effects of ocular BDNF. In sum, exogenous BDNF modulates the differentiation of retinotectal circuitries and dose-dependently shifts lateralized visuomotor processing towards the noninjected side. Since these effects are opposite to embryonic light stimulation, it is unlikely that the impact of light onto asymmetry formation is mediated by retinal BDNF.

Development and function of lateralization in the avian brain

The avian brain is functionally lateralized. Different strategies of choice (within and between modalities) are adopted by each hemisphere. Visual lateralization has been studied most but attention to auditory, olfactory and magnetic cues is also lateralized. The left hemisphere (LH) focuses on cues that reliably separate pertinent stimuli from distracting stimuli (e.g. food from pebbles, odour cues from attractive visual cues, magnetic cues from other cues indicating location), whereas the right hemisphere (RH) has broad attention and is easily distracted by novel stimuli. The RH also controls fear and escape responses, as in reaction to predators. Exposure of the embryo to light just before hatching, when the posture adopted occludes the left eye (LE) but not the right eye (RE), leads to the development of asymmetry in the visual projections to the pallium and enhances the ability of the RE/LH to inhibit attention to distracting visual cues and of the LH to inhibit the RH, but has no effect on the RH's interest in novelty. Exposure to light before hatching has both short- and long-term consequences that are important for species-typical behaviour and survival. For example, on a food search task with a predator presented overhead, dark-incubated chicks perform poorly on both aspects of the task, whereas light-exposed chicks have no difficulty. Steroid hormone levels prior to hatching modulate light-dependent development of asymmetry in the visual projections and consequently affect neural competence for parallel processing and response inhibition. Differences between lateralization in the chick and pigeon are discussed.

Animal lateralization and social recognition: quails use their left visual hemifield when approaching a companion and their right visual hemifield when approaching a stranger

Quails were tested for leftward and rightward turning preferences in a detour task. When facing a mirror located behind a barrier composed of vertical bars, quails showed a striking population-level preference for turning leftward. In order to check whether the asymmetry reflected a motor or a sensory (i.e. visual hemifield) bias, in a second experiment quails were reared in pairs and then tested in the detour task with a familiar (companion) or an unfamiliar (stranger) conspecific as a target. Quails turned leftward when viewing the stranger, but they turned rightward when viewing the companion. These findings are discussed in relation to current evidence for brain lateralization in response to social stimuli in non-human animals.

Asymmetrical participation of the left and right hippocampus for representing environmental geometry in homing pigeons

Control, right and left HF lesioned homing pigeons (Columba livia) were trained to locate a goal in one corner of a rectangular enclosure with a distinctive feature cue. Probe tests revealed that all groups were able to encode in parallel geometric (enclosure shape) and feature information, and in the absence of one of them, they could us the other to locate the goal. However, left HF lesioned pigeons learned the task at a faster rate, and when the geometric and feature information were set in conflict, they relied more on the feature cue compared to control and right HF lesioned pigeons. It was also found that pigeons, independent of group, trained to a goal adjacent to the feature cue learned the task in fewer sessions and relied more on feature information compared to pigeons trained to a goal opposite the feature cue. The latter group relied more on geometric information. The results support the hypothesis that the left HF plays a more important role in the representation of a goal location with respect to environmental shape/geometry. We further propose that the observed functional asymmetry can be explained by the lateralized properties of the pigeon tectofugal visual system.

Light experience and the development of behavioural lateralization in chicks

Chicks searching for food grains against a background of unfamiliar pebbles usually peck pebbles less when using the right eye (RE), or both eyes, than when using the left eye (LE), provided that the embryo's RE has been exposed to light (Li), as is normal. When pecking is fast this right/left difference is mainly due to a heightened ability of RE chicks to inhibit premature pecks (and inappropriate responses in general). Dark incubation (Da) abolishes this ability in RE chicks, and RE and LE chicks show similar frequent pebble pecks. We show now that, under conditions that cause cautious pecking, both Li and Da chicks show a new effect: in both cases LE chicks peck pebbles more than RE chicks, probably because of the novelty of pebbles. Interest in novelty in LE chicks is known to be unaffected by light in incubation. Age-dependent effects are also important. RE and LE chicks, which had either the LE or RE exposed to light before hatching, were tested on days 3, 5, 8 or 12 post-hatching, under conditions giving normal fast pecking. Artificial exposure of the embryo's LE to light reversed the lateralization: in general, chicks using the light-exposed eye performed well at all ages. Irrespective of which eye system had heightened ability to inhibit pebble pecks, RE performance differed from usual on 2 days, whereas LE chicks showed no age-dependent changes. Changes confined to the RE system, therefore, affect behaviour independently of lateralization of the ability to inhibit inappropriate response.

Organization of telencephalotectal projections in pigeons: Impact for lateralized top-down control

Birds display hemispheric specific modes of visual processing with a dominance of the right eye/left hemisphere for detailed visual object analysis. In pigeons, this behavioral lateralization is accompanied by morphological left-right differences in the ascending tectofugal pathway. This system is also asymmetrically modulated by descending telencephalotectal input whereby the left forebrain displays a much more pronounced physiological control over ipsilateral left and contralateral right visual thalamic processes. In the present study we aimed to answer the question if this top-down asymmetry that up to now had been demonstrated in single cell recording studies is due to anatomical asymmetries in the size of the fiber systems descending from the telencephalon to the tectum. We approached this question by means of a quantitative retrograde tracing study. Cholera toxin subunit B (CtB) was injected unilaterally into either the left or right optic tectum of adult pigeons. After immunohistochemical detection of CtB-positive cells, the number of ipsi- and contralaterally projecting neurons was estimated. Retrogradely labeled cells were located within the arcopallium, the hyperpallium apicale (HA) and the temporo-parieto-occipital area (TPO). Descending projections from HA, arcopallium, and TPO were mainly or exclusively ipsilateral with the contralateral projection being extremely small. Moreover, there was no difference between left and right hemispheric projections. These anatomical data sharply contrast with behavioral and electrophysiological ones which reveal an asymmetric and bilateral top down control. Therefore, contralateral and lateralized forebrain influences onto tectofugal processing are possibly not the direct result of asymmetrical descending axon numbers. Those influences emerge by a lateralized intra- and/or interhemispheric integration of ascending and descending input onto the rotundus.

Behavioral and neural lateralization of vision in courtship singing of the zebra finch

Along with human speech and language processing, birdsong has been one of the best-characterized model systems for understanding the relationship of lateralization of brain function to behavior. Lateralization of song production has been extensively characterized, and lateralization of song perception has begun to be studied. Here we have begun to examine whether behavior and brain function are lateralized in relation to communicative aspects of singing, as well. In order to monitor central brain function, we assayed the levels of several activity dependent immediate early genes after directed courtship singing. Consistent with a lateralization of visual processing during communication, there were higher levels of expression of both egr-1 and c-fos in the left optic tectum after directed singing. Because input from the eyes to the brain is almost completely contralateral in birds, these results suggest that visual input from the right eye should be favored during normal singing to females. Consistent with this, we further found that males sang more when they could use only their right eye compared to when they could use only their left eye. Normal levels of singing, though, required free use of both eyes to view the female. These results suggest that there is a preference for visual processing by the right eye and left brain hemisphere during courtship singing. This may reflect a proposed specialization of the avian left hemisphere in sustaining attention on stimuli toward which a motor response is planned.

Mechanisms of hemispheric specialization: insights from analyses of connectivity

Traditionally, anatomical and physiological descriptions of hemispheric specialization have focused on hemispheric asymmetries of local brain structure or local functional properties, respectively. This article reviews the current state of an alternative approach that aims at unraveling the causes and functional principles of hemispheric specialization in terms of asymmetries in connectivity. Starting with an overview of the historical origins of the concept of lateralization, we briefly review recent evidence from anatomical and developmental studies that asymmetries in structural connectivity may be a critical factor shaping hemispheric specialization. These differences in anatomical connectivity, which are found both at the intra- and inter-regional level, are likely to form the structural substrate of different functional principles of information processing in the two hemispheres. The main goal of this article is to describe how these functional principles can be characterized using functional neuroimaging in combination with models of functional and effective connectivity. We discuss the methodology of established models of connectivity which are applicable to data from positron emission tomography and functional magnetic resonance imaging and review published studies that have applied these approaches to characterize asymmetries of connectivity during lateralized tasks. Adopting a model-based approach enables functional imaging to proceed from mere descriptions of asymmetric activation patterns to mechanistic accounts of how these asymmetries are caused.

Representing the richness of avian spatial cognition: properties of a lateralized homing pigeon hippocampus

Brain organization and its relationship to behavior in any extant species is a reflection of a long evolutionary history of adaptive change. Therefore, it follows that the relationship between the hippocampus and spatial cognition in any species or taxonomic group would be characterized by features adapted to its spatial ecology. Birds are the animal world's supreme navigators, and aspects of their navigational ability are dependent on the integrity of the hippocampal formation. Using the homing pigeon as a model species, we review an accumulating body of data indicating that the avian hippocampus is functionally lateralized. The spatial response properties of left hippocampal neurons, as recorded in freely moving pigeons in a laboratory environment, differ from the response properties of right hippocampal neurons. Left hippocampal lesions generally disrupt navigational behavior under field conditions more than right lesions, while right lesions are more likely to disrupt goal localization behavior under laboratory conditions. We propose that the available data are consistent with a hypothesis of a left hippocampus more involved in navigational processes, and a right hippocampus more involved in representing the locations of events. We also discuss the extent to which the observed hippocampal lateralization should be viewed as an intrinsic property of the hippocampus itself or imposed by the lateralized properties of visual inputs originating in other brain regions. Whatever the nature of the observed hippocampal lateralization, it is likely one adaptive variation in hippocampal organization that supports the extraordinary spatial behavior of birds.

Topological relation of chick thalamofugal visual projections with hyper pallium revealed by three color tracers

In birds, there are two visual projections from retina to higher pallium, i.e., tectofugal and thalamofugal pathways. The latter one is lateralized in chick and suggested to be involved in visually evoked social behavior, like recognition of novelty, predator, and conspecific animals. We wanted to establish functionally relevant topological connection map between thalamic nuclei and hyperpallium apicale (HA) and carried out tracing study with three color fluorescent tracers. The tracers were serially injected in HA either along with the medial-lateral (M-L) or anterior-posterior (A-P) axis. We found that M-L axis and A-P axis in HA were transferred into the dorsal-ventral axis and the medial-lateral axis, respectively within the nucleus geniculatus lateralis pars dorsalis (GLd). In another word, the medial part of nucleus dorsolateralis anterior thalami pars lateralis (DLLv) projected to anterior part of HA and the ventral part of nucleus dorsolateralis anterior thalami pars lateralis pas ventralis (DLLd) projects to lateral HA. This result suggests that thalamus would process information in parallel through each subnuclei and elaborate coordination among them in relation to topological map presented in higher pallium.

Asymmetrical modes of visual bottom-up and top-down integration in the thalamic nucleus rotundus of pigeons

The aim of this study was to separate bottom-up and top-down influences within cerebral asymmetries. This was studied in the lateralized visual system of pigeons by recording from single units of the left and right diencephalic nucleus rotundus of the tectofugal pathway while visually stimulating the ipsilateral and/or contralateral eye. Analyses of response latencies revealed rotundal neurons with short and/or late response components. Cells with short latencies very likely represent bottom-up neurons participating in the ascending retinotectorotundal system. Because lidocaine injections into the visual Wulst produced a significant reduction of late response components only, neurons with long latencies were probably activated via a top-down telencephalotectorotundal system. The distribution and response characteristics of bottom-up and top-down neurons provided insight into several asymmetries of ascending and descending pathways. Asymmetries of the ascending retinotectorotundal system (bottom-up) were characterized by longer periods of tonic activation in the left and shorter response latencies in the right rotundus. Left-right differences in these responses probably facilitate faster access to visual input to the right hemisphere and a prolonged processing of this input in the left. The descending telencephalotectorotundal system (top-down) revealed a completely different lateralized organization. This system was characterized by long latency responses that exclusively derived from the left hemisphere, regardless of whether recordings took place in the left or the right rotundus. We assume that asymmetrical modes of visual processing within both hemispheres of the ascending tectofugal system are ultimately directed to left hemispheric forebrain mechanisms that subsequently generate executive control over sensory and motor structures.

Corticosterone treatment of the chick embryo affects light-stimulated development of the thalamofugal visual pathway

By injecting a single 60 microg dose of corticosterone into the eggs of domestic chicks on day 18 of incubation, we have shown that elevated levels of this hormone affect the development of asymmetry in the visual projections from the thalamus to the Wulst regions in the left and right hemispheres of the forebrain. In vehicle-treated (control) embryos this visual pathway develops asymmetry in response to light stimulation during the final stages of incubation, when the embryo is oriented so that its left eye is occluded by its body and its right eye can be stimulated by light entering through the egg shell. Pre-hatching exposure to light leads to more projections from the left side of the thalamus to the right Wulst than from the right side of the thalamus to the left Wulst, as confirmed here by injection of the tracers Fluorogold and Rhodamine into the left and right Wulst followed by counting the number of labelled cell bodies in the thalamus (asymmetry greater in males than females). The chicks injected with corticosterone pre-hatching did not develop any group bias for asymmetry in response to light exposure before hatching. They were random with respect to presence/absence of lateralization and, when present, the lateralization was not as strong as in the controls and its direction was random. The corticosterone-treated group had fewer projections from the left side of the thalamus to the right Wulst than did the controls. The results are considered with respect to maternal deposits of the hormone in the yolk and pre-hatching stress of the embryo.

Light experience and the development of behavioural lateralisation in chicks

In late-stage embryos of domestic fowl, exposure of the right eye to light entering through the shell induces asymmetry of the thalamofugal visual pathway, together with differences in performance according to whether the right or left eye (RE, LE) is in use (Behav. Brain Res. 38 (1990) 211). Nevertheless, at least some of the main specialisations of the right and left eye systems (RES, LES) are not dependent on such exposure. Higher ability of LES to assess and respond to novelty is present in dark-incubated (Da) chicks. This is probably also true of RES ability to control response, and specifically to inhibit shift to an alternative response (i.e. to a novel stimulus). We imprinted chicks on red table-tennis balls with a horizontal, white strip on their equator. At test, they chose between this and a ball with a vertical, white strip. Da chicks showed clear choice with the LE, but not with the RE. Unexpectedly, light-incubated (Li) chicks failed to show LE/RE differences in choice. Exploratory pecks at a novel feature were greatly reduced in Li. Two effects of light exposure on RES are likely. The first is greater use of RES in the home-cage, affecting what is learned about the companion ball. This may make RES more competent in assessing ball properties, and so explain the enhanced choice by RE, that abolished the RE/LE difference in Li. Secondly, the ability of RES to inhibit shift to an alternative response is enhanced. Light exposure and being female similarly opposed shift to the novel feature, but probably via different mechanisms. The effects of exposure are discussed as an example of the generation of a range of behavioural phenotypes, which are sustained within a single population by varying or frequency-dependent selection.