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:…were aimed at confirming the presence of PLCb1 in close vicinity to postsynaptic densities as previously observed by biochemical (Taguchi et al., 2007) and ultrastructural approaches (Fukaya et al., 2008), as well as to define the precise location of nuclear PLCb1 in native nervous tissue.
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