The CPGs distribute the control signals to each actuator from
a central unit, which can be prone to communication failures.
Another approach for joint-control locomotion is to run a cyclic
function on each module separately. To synchronize actions of the
modules, each module sends a message to its neighbors after a
fraction of the period is completed [27]. A similar approach is used
in role-based control in [28]. Synchronization can also be achieved
using artificial hormones [29,30], which flow though the modules
and trigger their actions. Another type of triggered synchronization
was proposed in [31]. More general types of motion can be achieved using non-cyclic functions, that can be derived
automatically using the concept of Genetic Programming [32,33].