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:Receptors containing the subunits 4 in the dentate gyrus, 5 in CA1 pyramidal cells, and 6 in the cerebellum are prominent examples of tonically activated GABAARs (Caraiscos et al., 2004; Farrant and Nusser, 2005).
Category: