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:For example, cocaine affects dopamine (DA), norepinephrine (NE), and serotonin (5-HT) reuptake, and the enhanced monoaminergic signals lead to addictive behaviors (Ritz et al. 1990; Ritz et al. 1987).
Category: