Avian auditory system. Ascending auditory inputs travel from hair cells to nucleus mesencephalicus lateralis pars dorsalis (MLD; avian homolog of mammalian central nucleus of the inferior colliculus), through auditory thalamus, nucleus Ovoidalis (Ov; avian homolog of mammalian medial geniculate nucleus). Ov then projects to forebrain region Field L2, thought to be homologous to thalamo-recipient layers III–IV of mammalian cortex (Wang et al., 2010; Dugas-Ford et al., 2012). Field L2 sends projections to adjacent areas, Field L1 and L3, which in turn project to the caudo-medial nidopallium (NCM) and caudal mesopallium (CLM and CMM). Reprinted by permission from Macmillan Publishers Ltd: Nature Reviews Neuroscience, Bolhuis et al., 2010.