Figure 3. Model for RIA function in gradient navigation. (A) In an isotropic environment, RIA monitors head movement via input from SMD class motor neurons and mediates negative feedback, limiting head deflection via compartmentalized Ca²⁺ signals of nrV and nrD that correlate with head bending. In gar-3 mutants, compartmentalized signaling is lost, leading to an increase in gait amplitude. (B) When perpendicular to a gradient, sensory changes across head swings cause global Ca²⁺ changes that are in phase with head bends in the unfavorable direction and antiphase with the favorable direction. This increases Ca²⁺ signaling and damps head bending in the unfavorable direction and extends it in the favorable direction. This asymmetry leads to curvature of locomotion in the favorable direction.