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Fig. 4. Resetting the phase of swimming by stimulating sint1. The firing
pattern in Lsint1 was recorded along with a record of behavior (upper
trace in each panel) during a continuous episode of swimming. (A–C)
Hyperpolarizing current pulses sufficient to prevent soma and axon spikes in
Lsint1 were applied via the recording electrode. The timing
and duration of pulses were varied (pulse timing indicated by solid lines
below the voltage traces). In each experiment, the interval between the
centers of Lsint1 bursts was measured during the 10 cycles preceding
the onset of the stimulus (indicated by vertical strokes above the voltage
recording). These measurements were used to calculate the means ±
S.D. of the swim period, which were then used to predict the time
of occurrence of the Lsint1 burst projected forward in time beyond
the period of stimulation, based on the assumption that stimulation of
Lint1 has no effect on pattern generation. The predicted times of the
center of Lsint1 bursts are shown as vertical lines above the voltage
recording, with the S.D. represented by horizontal tics through the
lines. The results show that the assumption fails and that the phase of
swimming behavior is reset by the stimulus. The difference between the
predicted and actual time of occurrence of the burst provides a quantitative
measure of phase resetting (see details in the text). (D) The experiment was
repeated with an extra burst driven in Lsint1. The extra burst also
reset the phase of swimming in a quantitative fashion (see text). The bridge
circuit used to deliver stimulating currents was imperfectly balanced and,
therefore, the absolute membrane voltage is not accurately represented during
periods of stimulation. This experiment was conducted 28 times in four
different whole animal preparations with consistent results.
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