Behavioural Brain Research 177 (2007) 61–69 Research report Light experience and the development of behavioural lateralization in chicks III. Learning to distinguish pebbles from grains L.J. Rogers a,∗ , R.J. Andrew a,b , A.N.B. Johnston a,1 a Centre for Neuroscience and Animal Behaviour, University of New England, Armidale, NSW 2351, Australia b Sussex Centre for Neuroscience, University of Sussex, Brighton, Sussex BN1 9QG, UK Received 6 September 2006; received in revised form 30 October 2006; accepted 2 November 2006 Available online 4 December 2006 Abstract 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. © 2006 Elsevier B.V. All rights reserved. Keywords: Lateralization; Development; Chicks; Light exposure; Incubation in darkness; Embryo; Pebble-floor task; Visual pathways 1. Introduction Behavioural lateralization in mammals is accompanied by differences in levels of neurotransmitters between the left and right hemispheres (e.g. noradrenaline and dopamine [11,24,39]) and in the dendritic location of NMDA receptors between the left and right sides of the hippocampus [17]. Pervasive left/right differences in the ratio of grey and white matter in humans [14] appear to reflect differences in the effectiveness of short- and long-range communication between cortical areas. However, ∗ Corresponding author at: Centre for Neuroscience and Animal Behaviour, Building W28, University of New England, Armidale, NSW 2351, Australia. Tel.: +61 267 733 969; fax: +61 267 733 452. E-mail address: lrogers@une.edu.au (L.J. Rogers). 1 Present address: SoNM Eskitis Centre for Cell and Molecular Biology, Griffith University, Nathan Campus, Nathan, Qld. 4111, Australia. clear asymmetries in discrete neural pathways in the forebrain have not been described in mammals. This gives special interest to the asymmetry in the ascending thalamofugal visual projections of the domestic chick, asymmet- rical organization of which results from exposure of the embryo to light during the final stages of incubation [18,33,35]. At this stage of development (the final 4 days of incubation), the chick embryo’s head is turned so that the right eye (RE) looks out- wards towards the translucent eggshell, and the left eye (LE) is shielded by the chick’s body [26]. As a result, light enter- ing through the shell and membranes stimulates only the neural pathways and centres supplied by the RE. Reversed monocular stimulation (exposure of the embryo’s LE only to light) during the crucial period prior to hatching reverses the asymmetry in the thalamofugal visual pathway [35]. Strikingly, such reversal also reverses asymmetry in behavioural measures, as seen in chicks tested using the LE or RE on tasks that either involve finding food grains against a background of pebbles or the evocation of ago- 0166-4328/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.bbr.2006.11.002