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:With regard to open studies, all of the open studies investigating the cognitive effects of rTMS in depression stimulated the left DLPFC via high frequency rTMS (Triggs et al., 1999; Martis et al., 2003; Fabre et al., 2004; O’Connor et al., 2005; Kuroda et al., 2006; Bloch et al., 2008; Vanderhasselt et al., 2009; Holtzheimer et al., 2010; Harel et al., 2011, in press; Leyman et al., 2011).
Category: