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:…(SNPs) compose the VZ while intermediate progenitor cells (IPCs) and basal radial glia (bRG), which are derived from VZ cells, populate the SVZ (Noctor et al., 2001; Gal et al., 2006; Kowalczyk et al., 2009; Fietz et al., 2010; Hansen et al., 2010; Shitamukai et al., 2011; Wang et al., 2011).
Category: