Figure 6.

A rapid depolarization in HS cells leads to steering in a stride-dependent manner

(A) dVm/dt (right HS cells) in segments drifting leftwards (−200 < Va < −150°/s) as a function of the stride cycle (left front leg) in 5-40^Leg > TNT (red, grand mean ± SEM, n = 8 fly cell pairs) or control (black, n = 6 fly cell pairs) flies.

(B) Mean dVm/dt before peak Vf as a function of the drift attenuation after peak Vf (see Figure 5) per walking segment (5-40^Leg > TNT, red: n = 18,319 segments; control, black: n = 3,065 segments). Linear regression fits are indicated (5-40^Leg > TNT: R = −0.01, p = 0.41; control: R = 0.38, p < 10⁻¹⁶, Student’s t test).

(C) Analysis in (B) was performed per fly (p = 0.0013, the rank-sum test).

(D) Schematic of the experimental configuration. The inlet shows ReaChR-expressing HS cells’ response to light (red shades) at different timescales (n = 9 cells).

(E) Confocal image of the split-HS line expressing ReaChR.

(F) Va traces in experimental (magenta, n = 11 flies) and control (gray, n = 8 flies) flies triggered at light stimulation.

(G) Mean change in Va (ΔVa) per fly upon light stimulation (p = 0.0091, the rank-sum test).

(H) Schematic of the experimental configuration.

(I) The leg’s horizontal position (n = 11 flies) and the fly’s Va (baseline subtracted per fly, n = 7 flies), triggered at light stimulation (red shade). Va traces are separated by the stride-cycle phase of the leg at stimulation, either in swing (light purple) or stance (dark purple). The inlet highlights the onset steering response, with the red arrowhead indicating the offset between the traces.

(J) Mean shift in leg position (Δposition) per fly (p = 0.0020, n = 11 flies, the rank-sum test).

(K) Steering onset latency for stimulation at swing (light purple) or stance (dark purple, p = 0.031, n = 7 flies, the signed-rank test).

(L) Mean stance duration of five consecutive strides around light stimulation (strides preceding versus at stimulation: p = 0.0020, n = 11 flies, the signed-rank test). Colored lines show individual fly data and green indicate the grand mean.

(M) Mean stance duration of strides preceding versus at light delivery, in strides with shorter (p = 0.0010, left) or longer (p = 0.32, right) preceding stance duration. n = 11 flies, signed-rank test.

See also Video S2.