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:Quinolinic acid (Sigma, St. Louis) was used to lesion the hippocampal formation and caudate nucleus (Schwartz et al., 1983) as described (Worley et al., 1986a).
Category: