Fig. 2: Direction selectivity is caused by the asymmetry of sound-evoked postsynaptic charge between FM directions.

a In vivo whole-cell recording schematic. b EPSCs (left) and IPSCs (right) evoked by FM sweeps with different rates. Traces are an average of six trials. Red lines, sound onsets and offsets. Black arrowheads, fast EPSCs. Open arrowheads, fast IPSCs. Asterisks, network suppression. c Magnified EPSCs and IPSCs from (b) at +20 oct/s (left) and −20 oct/s (right) FM sweeps. Orange (EPSC) and purple (IPSC) shaded areas highlight sound-evoked fast postsynaptic currents which are prominent only in preferred direction. d Quantitative analysis for the cell shown in (b) at each absolute FM rate. Left, the total charge of fast postsynaptic currents. Right, DSI_EPSC and DSI_IPSC calculated from the charge. No data point is shown for rates that did not trigger postsynaptic currents. e DSI_EPSC and DSI_IPSC averaged across cells (EPSC, n = 5 mice, 9 cells; IPSC, n = 4 mice, 7 cells). Results are mean ± SEM. f DSI_EPSC and DSI_IPSC are correlated (R = 0.522; p = 0.0031, two-sided t-test; n = 30 cell-rate pairs with DSI values for both EPSCs and IPSCs). Red line, regression curve. g Predicted timings of EPSCs, IPSCs, and spikes triggered by preferred and non-preferred FM sweeps in the temporal offset model. Dotted lines, peak timings of EPSCs. h EPSCs and IPSCs evoked by preferred (10 oct/s; top) and non-preferred (−10 oct/s; bottom) FM sweeps in another representative cell. i Magnified view of traces within gray boxes in (h). j Time by which EPSC peak precedes IPSC peak is not significantly different from zero in either direction (preferred: n = 30 cell-rate pairs, p = 0.976; non-preferred: n = 14, p = 0.800; preferred vs non-preferred: p = 0.817, two-sided t-test). Red lines indicate mean. k The time by which EPSC onset precedes IPSC onset is not significantly different from zero in either direction (preferred: p = 0.100; non-preferred: p = 0.549; preferred vs non-preferred: p = 0.153, two-sided t-test).