Development and function of lateralization in the avian brain

Lesion of the isthmo-optic nucleus impairs target selection for visually guided reaching

Neurons in the isthmo-optic nucleus (ION) of the avian midbrain receive input predominantly from the ipsilateral optic tectum and project to the contralateral retina. Therefore, lesion in the ION removes tectal efferent signals to the retina in birds. In the present study, we trained Japanese quail to reach a target stimulus on a touch-sensor monitor with their beak. ION lesions significantly decreased response accuracy when the target was presented simultaneously with distractors but not when presented alone. Thus the removal of the tectal efferent signals to the retina severely impaired target selection in a competitive visual search as if the ION-lesioning caused visual extinction, which is a neuropsychological deficit seen in human hemispatial neglect patients. We suggest that the avian tectum and its efferent path to the retina improve the accuracy of target selection for visual orienting and visually guided reaching with beak.

Threat perception in the chameleon (Chamaeleo chameleon): evidence for lateralized eye use

Chameleons are arboreal lizards with highly independent, large amplitude eye movements. In response to an approaching threat, a chameleon on a vertical pole moves so as to keep itself away from the threat. In so doing, it shifts between monocular and binocular scanning of the threat and of the environment. We analyzed eye movements in the Common chameleon, Chamaeleo chameleon, during avoidance response for lateralization, that is, asymmetry at the functional/behavioral levels. The chameleons were exposed to a threat, approaching horizontally from clockwise or anti-clockwise directions, and that could be viewed monocularly or binocularly. Our results show three broad patterns of eye use, as determined by durations spent viewing the threat and by frequency of eye shifts. Under binocular viewing, two of the patterns were found to be both side dependent, that is, lateralized and role dependent ("leading" or "following"). However, under monocular viewing, no such lateralization was detected. We discuss these findings in light of the situation not uncommon in vertebrates, of independent eye movements and a high degree of optic nerve decussation and that lateralization may well occur in organisms that are regularly exposed to critical stimuli from all spatial directions. We point to the need of further investigating lateralization at fine behavioral levels.

Hemispheric asymmetries: the comparative view

Hemispheric asymmetries play an important role in almost all cognitive functions. For more than a century, they were considered to be uniquely human but now an increasing number of findings in all vertebrate classes make it likely that we inherited our asymmetries from common ancestors. Thus, studying animal models could provide unique insights into the mechanisms of lateralization. We outline three such avenues of research by providing an overview of experiments on left-right differences in the connectivity of sensory systems, the embryonic determinants of brain asymmetries, and the genetics of lateralization. All these lines of studies could provide a wealth of insights into our own asymmetries that should and will be exploited by future analyses.

Auditory laterality in a nocturnal, fossorial marsupial (Lasiorhinus latifrons) in response to bilateral stimuli

Behavioural lateralisation is evident across most animal taxa, although few marsupial and no fossorial species have been studied. Twelve wombats (Lasiorhinus latifrons) were bilaterally presented with eight sounds from different contexts (threat, neutral, food) to test for auditory laterality. Head turns were recorded prior to and immediately following sound presentation. Behaviour was recorded for 150 seconds after presentation. Although sound differentiation was evident by the amount of exploration, vigilance, and grooming performed after different sound types, this did not result in different patterns of head turn direction. Similarly, left-right proportions of head turns, walking events, and food approaches in the post-sound period were comparable across sound types. A comparison of head turns performed before and after sound showed a significant change in turn direction (χ(2) (1)=10.65, p=.001) from a left preference during the pre-sound period (mean 58% left head turns, CI 49-66%) to a right preference in the post-sound (mean 43% left head turns, CI 40-45%). This provides evidence of a right auditory bias in response to the presentation of the sound. This study therefore demonstrates that laterality is evident in southern hairy-nosed wombats in response to a sound stimulus, although side biases were not altered by sounds of varying context.

Vision, touch and object manipulation in Senegal parrots Poicephalus senegalus

Parrots are exceptional among birds for their high levels of exploratory behaviour and manipulatory abilities. It has been argued that foraging method is the prime determinant of a bird's visual field configuration. However, here we argue that the topography of visual fields in parrots is related to their playful dexterity, unique anatomy and particularly the tactile information that is gained through their bill tip organ during object manipulation. We measured the visual fields of Senegal parrots Poicephalus senegalus using the ophthalmoscopic reflex technique and also report some preliminary observations on the bill tip organ in this species. We found that the visual fields of Senegal parrots are unlike those described hitherto in any other bird species, with both a relatively broad frontal binocular field and a near comprehensive field of view around the head. The behavioural implications are discussed and we consider how extractive foraging and object exploration, mediated in part by tactile cues from the bill, has led to the absence of visual coverage of the region below the bill in favour of more comprehensive visual coverage above the head.

Differential outcomes of unilateral interferences at birth

Behavioural modifications, including modifications of emotional reactivity, can occur following early experience such as handling (manual rubbing). Here, we investigated the effects of unilateral tactile stimulation at an early stage on emotional reactions later on. We handled newborn foals intensively on one side of their body. This early unilateral tactile experience had medium-term effects: the reactions of foals to a human approach, when they were 10 days old, differed according to the side stimulated at birth. Fewer right-handled foals accepted contact with humans, they delayed first contact longer and they evaded approaching humans sooner than did non-handled and left-handled foals. These results raise questions concerning the organization of neonatal care in animals and humans.

Determining the function of zebrafish epithalamic asymmetry

As in many fishes, amphibians and reptiles, the epithalamus of the zebrafish, Danio rerio, develops with pronounced left-right (L-R) asymmetry. For example, in more than 95 per cent of zebrafish larvae, the parapineal, an accessory to the pineal organ, forms on the left side of the brain and the adjacent left habenular nucleus is larger than the right. Disruption of Nodal signalling affects this bias, producing equal numbers of larvae with the parapineal on the left or the right side and corresponding habenular reversals. Pre-selection of live larvae using fluorescent transgenic reporters provides a useful substrate for studying the effects of neuroanatomical asymmetry on behaviour. Previous studies had suggested that epithalamic directionality is correlated with lateralized behaviours such as L-R eye preference. We find that the randomization of epithalamic asymmetry, through perturbation of the nodal-related gene southpaw, does not alter a variety of motor behaviours, including responses to lateralized stimuli. However, we discovered significant deficits in swimming initiation and in the total distance navigated by larvae with parapineal reversals. We discuss these findings with respect to previous studies and recent work linking the habenular region with control of the motivation/reward pathway of the vertebrate brain.

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.

Hemispheric specialization in Australian magpies (Gymnorhina tibicen) shown as eye preferences during response to a predator

Brain lateralization in birds is frequently expressed as a preference to view stimuli with one eye using the lateral monocular visual field. As few studies have investigated lateralized behaviour in wild birds, we scored eye preferences of Australian magpies (Gymnorhina tibicen) performing anti-predator responses. When animals deal with potential predators by mobbing them, constant assessment is needed to consider whether to approach, mob or withdraw. When presented with a taxidermic specimen of a monitor lizard, the magpies assembled on the ground close to the lizard and circled, pecked, jumped over, viewed and approached, or withdrew from it. Using video footage, the monocular fixations prior to or during performance of these activities were scored and the following significant eye preferences were found. Prior to withdrawing, the magpies viewed the lizard with the left eye (LE) (85% of events). Prior to approaching, the right eye (RE) was used (72%). Hence, the left hemisphere is used to process visual inputs prior to approaching the predator and the right hemisphere prior to withdrawing from it. This result is consistent with hemispheric specialization shown in other species, including humans. The LE was used also prior to jumping (73%) and prior to circling (65%), as well as during circling (58%) and for high alert inspection of the predator (72%). Mobbing and perhaps circling are agonistic responses controlled by the LE/right hemisphere, as also seen in other species. Alert inspection involves detailed examination of the predator and likely high levels of fear, known to be right hemisphere function.