Figure 2.

Action potentials in HVC_RA neurons evoke IPSPs in HVC_X neurons. A, Dual intracellular recordings show that DC-evoked action potentials in the HVC_RA neuron (bottom trace) can evoke IPSPs in the HVC_X neuron. B, An HVC_RA STA of the HVC_X neuron membrane potential, plotted relative to the HVC_RA action potential peak (0 ms; positive times follow the action potential), for the cell pair shown in A. A membrane hyperpolarization followed the HVC_RA action potential, indicating that HVC_RA neurons directly or indirectly drive IPSPs in the HVC_X cell. C, In some HVC_RA-HVC_X cell pairs, spike doublets in the HVC_RA neuron were necessary to drive IPSPs in the HVC_X cell (right traces), whereas single spikes failed to evoke any response (left traces), suggestive of disynaptic coupling.