Fig. 5. Inhibition of rhythmic swimming by manubrial stimulation. (A) Portions of a chart recording from one animal in which swims were recorded electromyographically using a suction pipette attached to the velum. Each swim was registered as a large downward deflection; shocks to the manubrium appear as small stimulus artefacts (downward in top series of traces, upward in bottom trace). Stimulus pulse trains were delivered at 3 Hz. The top traces show that a stimulus train containing two or more pulses caused a perceptible increase in the interval between successive swims. In the bottom trace, inhibition outlasted the 10.5 s stimulus by at least 6 s. (The swim deflections have been enhanced to improve clarity). (B) Relationship between the stimulus duration and the time interval from the end of the stimulus to the first post-stimulus swim; each data point was normalized by dividing it by the average pre-stimulus swim interval (N=3). The line drawn through the points was fitted by linear regression (slope, 1.3 of control swim interval/second of stimulus; y-intercept, 0.40 of control swim interval). (C) Relationship between the stimulus duration and the time interval between the first and second post-stimulus swim; data points were normalized as above. The line drawn through the points was fitted by linear regression (slope, 0.06 of control swim interval/second of stimulus; y-intercept, taken as 1.0 of control swim interval).