Figure 1.

Possible sources of song-related synaptic inputs onto HVC projection neurons. A, Schematic view of the forebrain premotor nucleus HVC (in red) and three afferent feedback streams that may have an impact on HVC projection cell activity during singing (in orange). B, C, Hypothetical intracellular traces during singing for the HVC projection neurons outlined in black. The synaptic potentials observed may be caused by sensory feedback (B; sensory model) or by premotor activity (C; motor model).