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:Amyloid-b peptides were reported to enhance vasoconstriction, reduce cerebral blood flow and
impair both functional hyperaemia and cerebral autoregulation in mice transgenic for mutant human amyloid-b precursor protein (APP) (Niwa et al., 2001, 2002a, b).
Category: