Fig. 1.

The preparation and fictive swimming. (A) Schematic representation of a stage 42 Xenopus larva dissected for recording from three ventral roots VR L5, L12 (on the left) and VR R7 (on the right). Swimming was evoked by electrical stimulation of the caudal skin on the left side using a glass suction electrode (SE). (B) Characteristics of stimulus evoked swimming. (i) Single 1 ms electrical pulse (Stim) evoked an episode of swimming lasting ∼12 s. (ii) Expanded excerpt showing eight cycles of swimming with ventral root activity alternating between left (L5) and right (L7) sides, and propagating from head to tail with a brief delay (L5,L12). (iii) In each cycle of activity, burst durations of approximately 20 ms occurred at cycle periods of ∼50–100 ms. Frequency was calculated as 1000/cycle period in milliseconds.