Lateralised brain function in anurans: comparison to lateralisation in other vertebrates.

In recent years researchers have begun to investigate lateralisation of behaviour in amphibians. Given the mounting evidence of lateralisation in birds and mammals, and even reptiles, over the past two or more decades, it is not surprising that amphibians have attracted attention in this context. In particular, the evidence for lateralisation in fish has provided a strong basis for this research. This paper summarises the currently available information on lateralisation in anuran amphibians and discusses it in comparison to lateralisation in other vertebrate species, beginning with examples of motor lateralisation and then discussing functional asymmetries that occur between the left and right sides of the brain. The latter are manifested as side biases in responding to different stimuli or, in a number of non-amphibian species, revealed by monocular testing. Most of the examples discussed refer to lateralisation present at the level of the forebrain hemispheres, and so represent hemispheric specialisation. Lateralisation usually refers to examples in which there is a population bias for the majority of individuals in a population to be lateralised in the same direction. In other words, there is a significant skew in the frequency distribution. Such population biases in lateralisation are now known to be widespread among the vertebrates and, as shown, there are some surprisingly similar patterns of lateralisation in those species of fish, amphibians, reptiles, birds, and mammals that have been studied so far. It is also noted that, despite their ubiquity in vertebrates, far from all forms of lateralisation develop solely, or even largely, according to genetic determinants. In fact, the clear and powerful influences of environmental stimulation on development of some kinds of lateralisation in birds provide a basis for similar investigations in anurans.