Supplementary Figure 1: Short-term depression is an intrinsic property of ORN-to-PN synapses.

ORN axons in the antennal nerve were stimulated with a train of 20 stimuli at 10 Hz (as in Figure 1b,c). Evoked EPSCs were recorded from PNs in whole-cell voltage clamp mode, both before and after blocking synaptic inhibition (with bath application of 25 – 50 μM CGP54626 and 5 μM picrotoxin). a) EPSC amplitudes evoked by each stimulus in a 10 Hz train, normalized to the first EPSC in the train before averaging across PNs, mean ± s.e.m., n = 4 PNs). Blocking inhibition had little effect on the dynamics of short-term depression at this presynaptic firing rate. b) EPSCs evoked by the entire 10 Hz train (averaged across 4 PNs, 2-5 trials per PN). EPSCs were normalized to the amplitude of the first EPSC prior to averaging. c) The first EPSC evoked by the train (arrow indicates stimulus time; stimulus artifact is blanked and mended by interpolation. When inhibition was blocked, some EPSCs were contaminated with currents arising from unclamped spikes in the PN. We excluded experiments where the rate of unclamped spikes was particularly high, but it should be noted that the occurrence of some unclamped spikes makes it difficult to precisely estimate EPSC amplitudes under these conditions.