Behavioural and neural lateralisation of vision in courtship singing of the zebra finch
Résumé
Lateralised function has been observed in a number of animal species. Most studies on the lateralisation of visually guided behaviour indicate a preferential use of the right eye/left hemisphere in food discrimination in chicks, pigeons and zebra finches. One study reported a right eye/left hemisphere dominance in courtship behaviour of male zebra finches, but this result was later disputed. Here we provide clear evidence of lateralised visual function in zebra finch courtship singing, and initial evidence for neural lateralisation. Behavioural experiments using the temporary occlusion of one eye showed that, when presented with a female, male birds tended to start singing later and sang significantly less in both monocular conditions than in binocular condition. Most importantly, birds sang 1.2 times more when using their right than left eye, and they especially sang significantly more motifs. At the central level, the evaluation of the density of ZENK- or Fos-positive cells in the optic tectum showed that the expression of these immediate early genes was significantly higher in several layers of the left than the right optic tectum. The fact that birds sang significantly more motifs when using their right than left eye suggests that there is a preference for visual processing by the right eye during courtship singing. A functional predominance of the left hemisphere processing is further supported by the significantly higher level of expression of immediate early genes in the left optic tectum. Both of these results are consistent with the proposed specialization of the avian left hemisphere in sustaining attention on stimuli, in this context the female zebra finch, to which a motor response is planned. In the future, simultaneous recordings of neuronal activity from both hemispheres will allow us to further characterize such hemispheric specialization.