Figure 1.

Experimental setup and analysis. (A) Diagram illustrating the closed-loop experimental setup. A moving grating is shown to a head-restrained larva (the grating speed is represented by the red arrow) and its behavior is monitored. A closed-loop environment is created such that, for a gain setting different from 0, swimming results in a deceleration of the grating. The scale bar at the bottom right is 1 mm. (B) Eight frames showing the automated reconstruction of the tail of a larva as it swims. The tail is reconstructed with 10 points. The frames shown are extracted from the full 10 s rep shown in (D). In particular, every second frame is shown from the start of the sixth bout, the full extent of which is shown in (C). The cumulative sums of the angles of the three most rostral and caudal tail segments can be obtained from this reconstruction and are plotted in (C) and (D) in red and black, respectively. The analysis can automatically detect the beginning and end of bouts, shown by green and blue vertical lines respectively, and the extrema of the tail angles, labeled with circles on the more caudal trace. These extrema are used to determine the instantaneous tail beat frequency, which is plotted for the entire 10 s trial in (F). This particular rep was carried out in low gain. The forward speed of the grating throughout the rep is shown in (E).