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:…has already been described in the reactive astroglia of other brain areas (sahin Kaya et al. 1999; clarke et al. 1994; Krum and Rosenstein 1999; Eliasson et al. 1999; Frisen et al.1995; Kalman and ajtai 2001), although the articles are not concordant with how long it lasts after traumatic insults.
Category: