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:This is supported by evidence that the degree of locomotion following administration of rewarding drugs correlates with extracellular DA levels in Nac (Miczek et al., 2011, Shimamoto et al., 2011, Valenti et al., 2012).
Category: