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:…however, nothing is known about the manufacture of E-CSF, although it has been demonstrated that this fluid plays a crucial role in early brain development, through the set of specific proteins and morphogens it contains (Gato et al., 2005; Parada et al., 2005a,
2008a,b; Martin et al., 2006).
Category: