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:It is unusual to have variability and asymmetries in Drosophila neural circuits
(Ohyama et al., 2015; Berck et al., 2016; Schlegel et al., 2016; Jovanic et al., 2016; Schneider-
Mizell et al., 2016) but it has been observed before (Takemura et al., 2015; Tobin et al., 2017;
Eichler et al., 2017).
Category: