Royal Society of NSW News & Events

Royal Society of NSW News & Events

1136th General Monthly Meeting

"Why did the vertebrate brain become lateralised?"

Lesley Rogers, Professor of Neuroscience and Animal Behaviour, University of New England

Wednesday 6 July 2005, 7 pm for 7.30
Conference Room 1, Darlington Centre, City Road, University of Sydney


Until recently it had been thought that specialization of the hemispheres to carry out different functions (i.e. brain lateralization) was a unique characteristic of humans, apparently explaining our ability for language and other superior cognitive abilities. We now know that lateralization of the brain evolved very early in vertebrates. Why did it evolve? This question is particularly pertinent when we consider that several species have been shown to detect an advancing predator more rapidly, and escape more readily, when the approach is from the left side (under the control of the right hemisphere). Predators could take advantage of this side bias. This obvious disadvantage must be counteracted by some advantage(s), and the latter may be found in social behaviour. This will be discussed and evidence for social species being lateralized at group level will be presented. The individual benefits from having a lateralized brain when several tasks have to be carried out at the same time (e.g. being vigilant for predators and searching for food) will also be discussed. In addition to these questions of function and evolution, the talk will cover the interactive influences of genes, hormones and experience on the development of brain lateralization.


Lesley Rogers is Professor of Neuroscience and Animal Behaviour at the University of New England, and coordinator of the Centre for Neuroscience and Animal Behaviour. She obtained her first degree (with Honours in zoology) at Adelaide University and her D. Phil. at Sussex University. Subsequently Sussex University awarded her a Doctor of Science. She is well known nationally and internationally for her research on the development and evolution of brain and behaviour, with a focus on hemispheric specialization (lateralization), and has published close to 200 scientific papers and 14 books. In fact, her discovery of lateralization in the brain showed that it is not a unique characteristic of humans and this work was among the few studies that established the now large field of research on lateralization in animals. She is a Fellow of the Australian Academy of Science and serves on its council. In addition to her interests in brain and behaviour, she is interested in higher cognition in animals and has played an active role in animal welfare, as Chair of her university's Animal Ethics Committee for a number of years and then as a member of the NSW Animal Research Review Panel. In 2004 the Royal Society of NSW awarded her the Clarke Medal for research in zoology.

Report on the General Monthly Meeting by Jak Kelly

It has been believed for centuries that our lateralized brains made us different from all other animals. A mounting body of field work and laboratory experiments over the last thirty years however indicates that the specialised lateralized brain evolved much further back in history than humans or even primates. Primates show hand preferences in feeding and tool use related to brain lateralization. It occurs in fish and is at present even being sought in invertebrates. Professor Rogers discussed her ground-breaking work on chickens. She found that they could be lateralized by exposing one eye to light, which they do naturally by turning their heads at day 18 to occlude the left eye and expose the right to light penetrating the translucent shell. Manipulating the chicken to reverse the eyes' exposure reverses the brain lateralization and hatching in the dark removes it. Injecting hormones into the shell also affects lateralization. The lateralization is thus a combination of genetics, hormones and training, with males being more asymmetric than females. Experiments with birds, and lizards and toads, show a clearly divided visual field with a tendency to attack if approached from the left. In general the right hemisphere [left eye] is used for rapid reaction events, such as escape from predators and the left hemisphere for activities that require more consideration, such as choosing food and prey capture. Species which have strong social interactions, such as fish which school and birds which flock have the same hemispheric bias. In many solitary animals bias tends to be randomly distributed. Why such asymmetry? It enables two tasks to be handled simultaneously with greater efficiency, as experiments show, and there are social advantages in having your companions react more predictably.

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