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:…neural network connectivity between brain regions increasingly has been proposed as a key characteristic underlying memory deficits in amnestic mild cognitive impairment (aMCI), which has a high risk of conversion to Alzheimer's disease (AD) (Bai et al., 2009a, 2009b; Sorg et al., 2007).
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