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:…of the most abundant synaptic proteins, Ca2+/calmodulindependent protein kinase II (CaMKII), is concentrated at postsynaptic densities (PSDs) in spines (Kennedy et al., 1983), along with downstream substrates, including NMDA receptors (NMDA-Rs) and AMPA-receptors (AMPA-Rs) (Yoshimura et al., 2000).
Category: