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:…stages of AD, neuropathologic changes are already present in medial temporal regions (hippocampal formations, parahippocampal gyrus, and entorhinal cortex), areas which are critical for long-term episodic memory (Blennow, de Leon, & Zetterberg, 2006; Morris et al., 2001; Sarazin et al., 2010).
Category: