Fig. 1.

Schematic of the recording design used in this study. A: a 16-channel, 4-tetrode recording array was placed in the cortical song nucleus HVC in the zebra finch brain. Bipolar stimulating electrodes were placed in its efferent projection targets, the song motor nucleus RA, and song basal ganglia, Area X. Arrows denote a subset of connections among song system nuclei. B: a simplified diagram of HVC shows the tetrode configuration. Tetrode shanks were placed 150 μm apart along the rostral-caudal axis. HVC neurons may project to either RA or Area X but not both. The axons of a 3rd group, interneurons (I), ramify solely within HVC. For this study, axons that terminated in Area X or RA were stimulated to antidromically identify single units in the context of a functioning forebrain network. LMAN, lateral magnocellular nucleus of the nidopallium; DLM, medial dorsolateral nucleus of the thalamus; nXIIts, tracheosyringeal portion of the hypoglossal nucleus.