Functional organization of the forebrain auditory centres of the European starling: a study based on natural sounds

The field L complex is thought to be the highest auditory centre and the input in the song vocal nuclei. Different anatomical and functional subdivisions have been described in field L. Auditory neurons of field L are well activated by natural sounds and especially by species-specific sounds. A complex sound coding appears to exist in field L. However, until now, the spatial organization of the different functional subdivisions has been described only using artificial sounds. Here, we investigated the spatial distribution of neuronal responses in field L to species-specific songs. Starlings seemed to be a very appropriate species for this investigation, both because of their complex vocal behaviour that implies different levels of categorization and their neuronal responses towards complex song elements. Multi-unit recordings were performed in wild starlings that were awake. The method of backward correlation was used to visualize the functional organization and we represented the neuronal responses as both activity maps and correlation maps. The use of natural sounds allowed us to define several functional sub-areas with different neuronal processing. These results show that field L is involved in a more complex task than simple frequency processing.