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:In mice transgenic for mutant human APP, the increase in amyloid-b peptides reduced cerebral blood flow through enhanced vasoconstriction, and impaired both functional hyperaemia and cerebral autoregulation (Niwa et al., 2001, 2002a, b).
Category: