Fig. 2.

Current injection into R3b1 elicits either the crawling or the swimming motor pattern. In isolated nerve cords, 3–4 nA of current was injected into R3b1 during the times indicated bygray bars at the top of each set of traces. Current injection caused increased spiking of R3b1, as monitored in the extracellular connective (conn 5/6) recording in each trace. Spikes were counted manually, and the spike frequency (measured in 2 sec bins) is indicated in each set of traces. a, Schematic drawing of the isolated nerve cord preparation. b, Intracellular recording of a CV neuron and extracellular recording of a DP nerve exhibit the crawling motor pattern. Black bars below DP trace indicate time of fictive contraction, based on peak firing of cell 3. c, Stimulation of R3b1 in a different preparation produced approximately the same firing frequency in R3b1 but elicited the swim motor pattern. CV and cell 3 spikes (in the DP recording) increase in frequency and then occur as bursts as swimming begins. In this case, swimming continued for many cycles after current injection ceased. Note that the period of swimming is much shorter than that of crawling. A portion of the DP trace has been expanded to show details of the burst pattern in cell 3.