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:Interestingly, recent studies demonstrate that co-administration of L-DOPA with a neuroprotective agent that inhibits excitotoxicity, oxidative stress, and neuroinflammation reduces LID in animal models of PD (Spinnewyn et al., 2011; Aron Badin et al., 2013).
Category: