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:The neuro-protective efficacy of this drug has been reported after different types of lesions in-vitro (Hutter-Paier et al., 1996a,b) and in-vivo (Akai et al., 1992; Masliah et al., 1999; Schwab et al., 1997).
Category: