Fig. 8. Widespread ultradian oscillation in clock neurons driven by xCEOs.

Among the 150 central clock neurons, many subtypes arborize their processes in the aMe and others do not. In each brain hemisphere, there is one set of xCEO neurons. The two sets of xCEO neurons mutually connect with each other via their dorsal commissure, producing synchronized ultradian bursting across the brain. By making monosynaptic connections with circadian clock neurons in the aMe, xCEOs pace synchronized ultradian bursting in most clock neuron subtypes to support free-running circadian locomotor rhythms.