Combined blockade of AMPARs and NMDARs eliminates excitation in IC single units. Rate-level functions and PSTHs for two IC units showing combined effects of NBQX and CPP are depicted. A, Onset unit (BF, 23.7 kHz; MT, 59 dB SPL; minimum latency, 14. 8 ms). B, Sustained unit (BF, 57.7 kHz; MT, 34 dB SPL; minimum latency, 10. 6 ms). Responses were obtained before (PREDRUG), during (NBQX & CPP), and after (RECOVERY) drug application. PSTHs show responses at two sound levels for each test condition. Combined application of NBQX and CPP completely eliminated unit responses at each sound level tested. The bin width of PSTHs was 1 ms. The number in the bottom right of each PSTH represents total spikes. The tone duration (black bars) was 61 ms including 0.5 ms rise and fall. In all figures, spikes counts and PSTHs are based on 32 stimulus repetitions. Drug application times and currents are as follows: in A, NBQX & CPP, 18 min, −40 nA each; RECOVERY, 4 min; in B, NBQX & CPP, 15 min, −40 nA each; RECOVERY, 9 min. SPL, Sound pressure level.