Intrinsic and extrinsic contributions to auditory selectivity in a song nucleus critical for vocal plasticity

The development, maintenance, and perception of learned vocalizations in so ngbirds are likely to require auditory neurons that respond selectively to song. Neurons with song-selective responses have been described in several brain nuclei critical to singing, but the mechanisms by which such response properties arise, are modified, and propagate are poorly understood. The l ateral magnocellular nucleus of the anterior neostriatum (LMAN) is the outp ut of an anterior forebrain pathway (AFP) essential for learning and mainte nance of song, processes dependent on auditory feedback. Although neurons t hroughout this pathway respond selectively to auditory presentation of the bird's own song, LMAN is the last stage at which responses to this auditory information could be transformed before being transmitted to vocal motor a reas, where such responses may influence vocal production. Indeed, previous extracellular studies have indicated that LMAN's auditory selectivity is g reater than that at earlier stages of the AFP. To determine whether LMAN lo cal circuitry transforms or simply relays song-related auditory information to vocal control neurons, it is essential to distinguish local from extrin sic contributions to LMAN's auditory selectivity. In vivo intracellular rec ordings from LMAN projection neurons, coupled with local circuit inactivati on, reveal that much of LMAN's song selectivity is supplied by its extrinsi c inputs, but selective blockade of GABA receptors indicates that local inh ibition is required for the expression of song selectivity. Therefore, LMAN neurons receive highly song-selective information, but LMAN's local circui try can mask these selective inputs, providing a mechanism for context-depe ndent auditory feedback.