A total of three studies (Gallinat et al. 2003; Tsai et al. 2003; Bramon et al. 2006) published between 2003 and 2006 and comprising six independent samples were identified by the search strategy and met the inclusion criteria (Table 6). Where data were not available in an appropriate format, we attempted to contact authors directly, which resulted in all available data being included in the meta-analysis.
