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:For neuronal differentiation of the neurospheres, they were partially dissociated as above and seeded on polylysine/ laminin-coated coverslips in neurogenic medium containing DMEM/F12 (1:1), B27 supplement (1:50, Invitrogen,USA), glutamine 2 mM, 50 U/ml penicillin, 50 μg/ml streptomycin, and 10 ng/ml mNGF (Alomone), as previously reported in [21].
Category: