Figure 5. Residual internal pressure accounts for current amplitude in soft and stiff worms.

(A) Experimental data (dots) and the average theoretical prediction (lines) for force-indentation relations. Best fit of pooled data for soft worms gives ${\displaystyle p}$ = 1.6 kPa; individual values are variable, with estimated $p$ in the range 0.04–16kPa. (B) The vertical deformation profiles $u_z$ vs the position $y$ along the longitudinal axis for stiff (red) and soft (blue) animals. Note the widely differing profiles for the force-clamped curves. (C) Experimental (dots) and theoretical (mean value as continuous lines) peak current for force (top) and displacement-clamped (bottom) stimuli. The current is normalized by the mean peak in soft and stiff worms, respectively. (D) Peak current vs the pressure $p$, which shows that the model (continuous lines are the mean; dot-dashed lines are above/below one standard deviation) captures experimental trends (dots). Experimental data reproduced from Eastwood et al. (2015) and Eastwood et al. (2019) and derived from 4 and 21 recordings in the stiff (red) and soft (blue) conditions, respectively.