EFFECT OF BRAIN ASYMMETRY ON LEARNING AND FEEDING IN CHICKENS LESLEY J. ROGERS SUMMARY This paper suggests that asymmetry of brain function may have important implications for display patterns and social organisation in chickens. The functions known to be asymmetrically organised in the chicken brain are discussed together with the techniques which have been used to reveal these asymmetries. Hemispheric and eye-eye asymmetries have been demonstrated. The latter are manifest in behaviour of the whole animal, such that attack and copulation responses are more likely to be elicited by stimuli in the left visual field, and the right eye is better in performing visual discrimination learning to feed. Suggestions are made for management relating to the use of polypeepers and position of feeders in the cage. The effects of domestication, incubation conditions and hormonal treatment on asymmetry are discussed. I 0 INTRODUCTION The left and right hemispheres of the chicken brain have been shown to have different functions in the control of many behaviours. Such asymmetry of brain function has now been reported for a number of species (Harnard et al. 1977; Denenberg 19811, but in avian species it has special relevance to the behaviour of the whole animal. The reason for this is that the optic nerve fibres decussate completely in birds, and birds have no major interhemispheric connecting system such as the corpus callosum of mammals. Thus information received by one eye is processed largely by contralateral side of the brain (Rogers 1985). In other words, information processing by the left-eye-system, LES, differs from that of the right-eye-system, RES, and therefore the left and right eyes look at different worlds and direct different behavioural sequences. That is, in birds, asymmetry of brain function becomes manifest at the perceptual level and, for the visual system at least, it becomes an asymmetrical template imposed upon the space surrounding the animal. As a consequence of this, asymmetry of brain function may have become manifest in social behaviour, and so play a role in the management of commercial chicken flocks. II . ASYMMETRY IN THE CHICKEN BRAIN Asymmetry of function in the chicken brain (australorp x leghorn) was' first demonstrated by unilateral administration of cycloheximide (CXM), an inhibitor of ribosomal protein synthesis, into either the right or left forebrain hemisphere on day 2 of post-hatching life (Rogers and Anson 1979). Treatment of both hemispheres or of the left hemisphere alone was found to retard learning of a visual discrimination task, in which the chicken has to search for grains of food mash scattered on a background of small pebbles (Rogers et al. 19741, Treatment of the ,right hemisphere with CXM was found to have no effect on this learning performance; these birds learnt as well as saline-treated controls. The learning deficit which follows treatment of the left hemisphere can be detected long after the CXM has ceased to inhibit protein synthesis. Learning performance is usually measured in the second Physiology Department , University of New England, Armidale, New South Wales 2351, Australia.