Figure 1.

Sagittal diagrams of songbird brain. (a) Anatomical relations between song nuclei (white) in which ZENK expression was induced by the act of singing. Black arrows show the direct motor pathway that innervates the vocal organs and produces learned song. Shaded arrows show links between other song system nuclei (5). The connections between RA and mMAN are described elsewhere (6). (b) Anatomical relations between forebrain auditory relays (white) in which ZENK expression was induced by hearing song. Thick black arrows show the major ascending auditory pathway, which ends in L2; thin black and gray arrows show some of the connections between forebrain auditory regions and the channeling of this input into HVC. Though not shown, NCM and cHV are reciprocally connected (7). Expression in the 12th and cochlear nuclei was not investigated. DLM, medial nucleus of dorsolateral thalamus; nXIIts, tracheosyringeal portion of the hypoglossal (12th) nucleus; Ov, nucleus ovoidalis. Other abbreviations are as used in the text.