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:, 1995) and in vitro (Fellous and Sejnowski, 2000), and their spike timing reliably shifts forward along the u-cycle phase during spatial behavior of the animals (O’Keefe and Recce, 1993).
Category: