Figure 4. Controlling AIY activity is sufficient to evoke chemotactic behavior.

a, Virtual light gradient algorithm (see supplementary method). At each time t, AIY::ChR2 animals (pttx-3::ChR2) are stimulated with 480 nm blue light with an intensity (I(n_x,n_y)) of the virtual gradient at the nose-tip position (n_x,n_y). b, Trajectories of AIY::ChR2 animals moving in a virtual light gradient (as in (a)) with a gradient direction at 45 degrees (black tick: mean direction of trajectory, grey bar: s.d., n=10). c, Top: A sample trajectory of an animal in (b). Bottom: Snapshots of the animal making a gradual turn to reorient itself to the gradient direction (pseudocolor: same as (a)). d, Magnitude of A_I (black), and S_I (blue, right axis), over a head swing, as a function of numbers of head swings during a gradual turn (n=5, from trajectories in (b), error bar: 1 s.d.). e, Model for chemotaxis in the virtual light gradient. f, Trajectories of center of mass of animals when the gradient direction was suddenly rotated (at times when the animal reached the red dots) by 180, 120 or 90 degrees.