Fig 3. Illustration of the PLM Response as in [11].

Constant stimulation of PLM neurons (corresponding to tail-touch) causes oscillation in body-wall motorneurons. This oscillation can be described as a 2D limit cycle, consistant with the observed 2D body shape dynamics of forward motion [29]. The center of this limit cycle is displaced in the full-dimensional space from the zero-input fixed point. We refer to the two oscillatory modes as the “plane modes”, and the displacement from the fixed point to the center of oscillation as the “displacement mode”.