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:…metabotropic and ionotropic glutamate receptors and the emergence of theta-rhythm and sharp-wave-related network activity, all of which promote state-dependent bidirectional effects on synaptic transmission and plasticity (Qin et al. 2005, Hu et al. 2007, Seol et al. 2007, Vyazovskiy et al. 2008).
Category: