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:Based on previous studies, bothmGluR1 andmGluR5 were very important for the regulation of pyramidal cell excitability (Mannaioni et al., 2001; Ireland and Abraham, 2002).
Category: