Extensive evidence has demonstrated that hemispheric specialization and behavioural lateralization are widespread among all vertebrate classes, and can not at all be any longer considered as unique to the human brain. Animal models can though now be used to look at the neuronal processes governing lateralized functions and to try and answer questions concerning the function, other than the structure, of cerebral lateralization. Birds provide a most interesting animal model, as the virtually complete decussation at the optic chiasm enables selective engagement of left and right cerebral structures. We report data recently obtained in our own and in several other laboratories from birds (mostly from the domestic chick, but also from pigeons and other avian, but not only, species) observed in monocular conditions of vision (i.e., through the use of eye patches, or by simply scoring the bird's spontaneous lateral fixations). A lateralised bias in behaviour is found in many complex tasks, bettering our understanding of the cognitive aspects of animal brain lateralization: the left and right cerebral structures are differentially involved in the different tasks, such as those involving visual perception of objects, representation of space, working memory, etc. Striking similarities are found between data coming from the different animal species and our own. Ontogenetic and phylogenetic aspects of animal brain lateralization are also discussed.
Keywords: cerebral lateralization, brain asymmetry, brain lateralization, lateralization, laterality, evolution of lateralization, development of lateralization.