Figure 1

(A1) Voltage-sensitive dye recording of dorsal and a ventral excitatory longitudinal motor neurons, as well as a nerve, on which dorsal excitatory motor neuron bursts are recorded, in midbody ganglion 15. (Data in Figure 1A were kindly provided by Kevin Briggman from experiments described in [30].) Initially, in phase oscillations of the dorsal longitudinal excitatory (DE) and ventral longitudinal excitatory (VE) motor neurons with a period of about 20 seconds indicate fictive crawling. At the end of the recording, fictive swimming behavior commences. (A2) Zoom of fictive swimming motor pattern from (A1): DE and VE motor neurons oscillate out of phase and with a period of about one second. (B) Dorsal posterior (DP) nerve recordings from multiple ganglia during crawling demonstrate the phase lag between ganglia from front to rear. Downward arrows and lines indicate the start of a motor neuron burst for a selected cycle of fictive crawling. (Data kindly provided by Karen Mesce and Joshua Puhl.) (C) Simplified circuit schematic of a segmental oscillator of the swimming CPG and its intersegmental connectivity: component neurons are broken down into three phase groups, 0, 0.33 and 0.67, with the inter- and intrasegmental connectivity indicated. Less important elements are omitted from the schematic, that is, cells VI-2 and VI-119. The anterior projections are replications of the intrasegmental connectivity, whereas the posterior projections differ. Inhibitory motor neurons DI-102 and DI-1 participate in and can strongly influence the pattern produced. Only cells 28 and 27 have strictly reciprocal connectivity. (Original artwork adapted from [12], Figure 10, and from [5], Figure 15.)