Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:In many species, rhythmic movements have been proved to be the output of dedicated neural circuitries, the Central Pattern Generator(s) (CPGs1) (Marder, 2000; Marder and Bucher, 2001).
Category: