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:Such a process favors local systems to take over on long-distance brain connections and decreases intellectual abilities, (van den Heuvel et al., 2009) which lead to a hypothesis of a continuum in the intrinsic network degradation from normal aging to mild cognitive impairment to AD dementia.
Category: