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:Together with our earlier experiments demonstrating that Bdnf promoter IV transcription is induced upon activity-dependent CREB phosphorylation (Tao et al., 1998), these findings strongly suggest that the impairment in neuronal-activity dependent induction of Bdnf expression in CREmKI mice is due…
Category: