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:SN hyperechogenicity is associated with local abnormal iron accumulation (Berg et al. 1999b, 2002; Zecca et al. 2005), decreased neuromelanin (Zecca et al. 2005), and microglia activation (Berg et al. 2010) in addition to remote brain changes.
Category: