An electrophysiological and kinematic model of Paramecium, the “swimming neuron”
Fig 9
Simulation of the avoiding reaction.
A, Velocity v as a function of intraciliary calcium concentration [Ca2+] in the model. B, Angle θ of the rotation axis as a function of [Ca2+] in the model. C, Spinning speed ω as a function of [Ca2+] in the model. Angle and spinning speed increase at intermediate Ca2+ concentration, as implied by the spherical model in Fig 8F and 8D, Simulated model trajectory with three 2 ms current pulse stimulations of increasing amplitude. Images are shown at 400 ms intervals. Without stimulation, the organism swims in spiral, with the oral groove facing the spiral axis. A very small stimulation deviates the trajectory. Stronger stimulations produce avoiding reactions, with backward swimming and turning. E, Example of an observed Paramecium trajectory showing a directional change without backward swimming (right), followed by a full avoiding reaction (left). Images are shown at 400 ms intervals, starting on the right. F, Backward swimming duration (F1) and reorientation angle (F2) as a function of current amplitude for 2 ms pulses. Red and black curves show results for the same model but different initial positions of the oral groove, differing by a quarter of a cycle. G, Backward swimming duration (G1) and reorientation angle (G2) as a function of current pulse duration T with 100 pA amplitude. H, Reorientation angle vs. backward swimming duration in n = 1138 spontaneous avoiding reactions of Paramecium, showing a positive correlation (linear regression r = 0.2, p ≈ 10−11). About 15% of data points are not represented (larger angle or duration). Colors represent contour lines of the distribution.