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:Although early studies linked cFos expression to neuronal activity (Sommer et al., 1993, 1996), only recently these neurons were directly implicated in internal representation and behavioral expression of distinct memories (Cruz et al., 2013, 2014a).
Category: