Functional changes in field L complex during song development of juvenile male zebra finches

The field L complex is the highest station of the ascending auditory pathway and is thought to be the input stage of auditory information into the song system in birds. Multi-unit recordings were performed in awake, socially reared zebra finches, 30 and 60 days of age. The responses of the field L complex to synthetic and natural stimuli during important periods of song learning were investigated. According to neural responses in field L, three different functional areas could be distinguished, NA-L(30), NA2b(30) and NA2c(30,) in 30 days old birds. In 60 days old birds five different functional areas, NA-L(60), NA2a(60), NA2b(60), NA2c(60) and NA3(60), were recognised. Especially, NA-L increases its functional volume between the developmental stages. The different areas showed already mature neuronal response behaviours. No preference for a certain song type could be found at all ages. The incomplete functional organisation of the field L complex in young birds (30 days) is a possible reason for the nonselectivity in the song system at this age.