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:They demonstrated by in vitro and ex vivo studies that ATP1A1 mutants showed loss of pump activity and strongly reduced affinity for potassium, causing inappropriate depolarization of the cells (Beuschlein et al. 2013).
Category: