A simplified diagram of the song system.Dashed lines indicate indistinct anatomical borders. AreasL1, L2a, L2b, and L3 are collectively called field L. The primary source of auditory input to HVc (via the shelf) is areas L1 and L3 (Kelley and Nottebohm, 1979; Fortune and Margoliash, 1995; Vates et al., 1996). Thalamic auditory areas project primarily throughout L2a andL2b (L2b connection not shown) (Vates et al., 1996). The other nuclei afferent to HVc, mMAN (medial magnocellular nucleus of the anterior neostriatum), NIf (nucleus interfacialis), and Uva (nucleus uvaeformis), have not been characterized physiologically, although NIf andUva are thought to be involved in song production (McCasland, 1987; Williams and Vicario, 1993). The diagram also shows that HVc is part of the descending motor control pathway; HVc projects toRA (robust nucleus of the archistriatum), which directly innervates the motor neurons of the vocal musculature in nXIIts(tracheosyringeal part of the hypoglossal nucleus).