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:Furthermore, to confirm that decreases in Fos expression were not simply caused by decreases in the total number of neurons within connected nuclei, we also quantified the number of neurons (labeled by the neuron-specific nuclear protein NeuN; Mullen et al., 1992) within each nucleus analyzed for Fos (Experiment 2).
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