Clustered temporal pattern of C. elegans egg-laying behavior and its neuronal control. A) Cartoon representation of egg-laying behavior. Each red vertical bar indicates one egg-laying event; egg-laying shows a clustered temporal pattern: short hyperactive periods (pink) are interspersed by longer quiescent periods (gray). The egg-laying intervals within active states are termed intra-cluster interval (τ1); the intervals between the last event of one cluster and the first one of the next cluster covering an inactive state are termed inter-cluster interval (τ2). B) Neuronal circuit inducing individual egg-laying events. HSN autonomous spiking activity will activate vulval muscles (vm1 and vm2), both directly and redundantly through VC neurons. Vulval muscles are of two types, vm1 and vm2, and are connected by gap junctions. Their simultaneous contraction leads to transient opening of the vulva and a single egg being laid. VC has also been found to have an inhibitory effect on HSN.