Fig. 7.

Silencing local LMAN circuitry with GABA reveals persistently song-selective extrinsic inputs. A, GABA treatment inactivated the entire extent of LMAN, as indicated by examples from two birds (cases 1,2). All stained LMAN neurons shown were silenced by GABA application (darkspotsabove LMAN mark the drug bolus from the stationary pipette). B,LMAN neurons maintained selective subthreshold responses when the local circuit was inactivated with GABA. Selective subthreshold and suprathreshold responses to BOS versus reversed BOS (data not shown, but see C) are visible pre- and post-GABA. Although no spontaneous, song- or DC-evoked spiking occurred during GABA application, the same cell maintained selective subthreshold responses despite a greatly reduced amplitude of synaptic activity. Positive currents (+1 nA; 0.5 sec) injected after each playback evoked action potentials before and after GABA treatment but only small depolarizations in GABA. d′ values compare BOS (depicted) with reversed BOS (data not shown) responses. Thebottomrow depicts the timing of song playback and current injection. C, Normalized song-evoked responses from B reveal similar shapes and time courses of BOS responses with and without local circuit activity. The twotraces on theright contrast forward and reversed BOS responses in GABA (d′ = 1.18). The vertical scale bar on the right (1 mV) applies to middle andrightpanels. Verticaldottedlines in B andC mark the onset of song-evoked response from theleftmosttrace (pre-GABA).L, Lateral; M, medial;N/A, not available; R, rostral;V, ventral.