Task complexity matters: investigating behavioural lateralization in rats

Behavioural lateralization, such as hand and paw preferences, is a widespread phenomenon among humans and nonhuman animals. Task complexity is assumed to have an influence on behavioural lateralization, that is the strength of lateralization increases with increasing task complexity. However, systematic comparisons of different lateralized tasks in nonprimate species are rare. Therefore, this study aimed to investigate the influence of task complexity on paw preference in a rodent species, the laboratory rat, Rattus norvegicus f. domestica. Male and female rats were tested in five different paw preference tests, including complex tasks, such as food reaching, tool use or string pulling, and simple routine behaviours, such as climbing and standing. For all tests, the distribution of paw preferences was assessed, and the differences in strength and direction of lateralization were tested among the tests. The temporal consistency of paw preference was also investigated, and it was examined whether the paw used first indicates an individual's overall preference. Results showed that a large number of rats were strongly lateralized for two complex tasks (food reaching and tool use), whereas the vast majority was ambilateral for string pulling, climbing and standing. Furthermore, only food reaching and tool use were temporally consistent in the direction and strength of lateralization. Overall, strength decreased over time. Sex showed no effect, but individuals that used the left paw first were more strongly lateralized. In conclusion, task complexity can affect behavioural lateralization in rats; however, other attributes, such as task novelty, should also be considered. Moreover, artificial test situations, which favour the use of a single paw, likely reveal paw preferences, whereas routine behaviours or alternating paw use are associated with ambilaterality. These findings complement existing studies that focused on food reaching tests and underline the need for investigating behavioural lateralization in different contexts and test situations.