Fig. 7.

Rear premotor interneurons are coordinated with the heartbeat CPG and switch phase relations with the other HN interneurons. A: extracellular recordings from the front premotor HN(L,4) interneuron, middle premotor HN(L,6) interneuron, and both rear premotor HN interneurons, also on the left side. Dashed lines mark the position of the middle spike in the HN(4) (top trace), the reference, and are provided to facilitate observation of relative phasing. Color-coded different symbols above each burst denote the middle spikes of the other interneurons. Standard colors are used for the HN interneurons (see methods). The recording starts in the synchronous mode with the HN(4) interneuron leading, followed by the HN(6) interneuron and then by the HN(15) and HN(16) interneurons. After the switch into the peristaltic mode (arrow), the rear HN(15) and HN(16) interneurons are leading, followed by the HN(6) interneuron and, after a delay, by the HN(4) interneuron. B: the actogram demonstrates the timing relationship for the middle spike of 38 consecutive bursts across the switch between the 2 coordination modes (same symbols as in A). Note that the rear HN interneurons fire nearly in phase in both coordination modes. The shaded box represents the bursts shown in A. Time 0 corresponds to the cycle period (7.1 s).