Figure 5. Synaptic currents evoked by mechanical stimuli.
(A)Synaptic currents evoked by step displacements in four example cells (dark: +3 μm step, light: −3 μm step). Step onset occurs at the start of the first trace, step offset at the start of the second trace. The B1-high cell and the first B1-mid/low cell are “positive cells”. The second B1-mid/low cell is a “negative cell”. Scales are identical for all B1 cells.
(B) Synaptic currents evoked by sinusoidal stimuli (0.45 μm). Insets are expanded 10× horizontally and rescaled to arbitrary values in the vertical axis.
(C) Tuning curves showing synaptic current versus frequency, normalized to the maximum for each cell. For A2 cells, the response is measured as the average change in holding current during the stimulus (n=6 cells). For B1 cells, the response is calculated as the magnitude of the Fourier component of the holding current at the stimulus frequency (B1-high: n=7 cells; B1-mid/low: n=7 cells). Stimuli are 0.45 μm in amplitude. Note the similar tuning of synaptic currents in all the B1 cells (comparing currents in fru-Gal4 cells versus VT27938-Gal4 cells, p=0.2, bootstrapped K-S distance). Arrowheads represent modal best frequency for B1-high and B1-mid/low.
(D)Tuning curves for voltage responses recorded in the same cell types (recorded in current-clamp mode with voltage-gated conductances intact). In B1-high cells, voltage tuning is shifted to higher frequencies, as compared to synaptic current tuning (comparing voltage with current in fru-Gal4 cells, p<10−3, bootstrapped K-S distance). By contrast, in B1-mid/low cells, tuning is shifted to lower frequencies (comparing voltage with current in VT27938-Gal4 cells, p<10−4, bootstrapped K-S distance). Stimuli are 0.45 μm. This panel shows a subset of the B1 data in Figure 2 (here, n=5 A2 cells, 7 B1-high, 8 B1-mid, 6 B1-low); these are the data obtained from fru-Gal4 (B1-high) and VT27938-Gal4 (B1-mid/low).