br Conclusions br Acknowledgements This

Conclusions
Acknowledgements This research was supported by Grant no. BMBF 01EV0711 (German Ministry of Education and Research) and by the IMAGEN Project (PL037286) of the European Commission\'s 6th Framework Program (LSHM-CT-2007-037286). We acknowledge support by the German Research Foundation and the Open Access Publication Funds of the Technische Universität Dresden. We would like to thank Thomas Huebner for the preparation and implementation of the paradigm, Kathrin U. Mueller for her help in recruitment and assessment, and Julius Steding for his help in reliability analysis. Also, we are grateful to our participants, especially the participating adolescents and their families.
Introduction Attention-deficit/hyperactivity disorder (ADHD) is the most common neurodevelopmental disorder in children and adolescent, with a worldwide prevalence rate between 5.3% and 7.1% (Polanczyk et al., 2007). Research on gender differences in ADHD suggests a male-to-female ratio of 3:1 in population-based studies (Gaub and Carlson, 1997; Barkley, 2006), and between 5:1–9:1 in clinical samples (Gaub and Carlson, 1997; Sandberg, 2002). Girls have been underrepresented in past studies on ADHD (Mahone and Wodka, 2008), probably due to the predominance of male subjects in clinical settings (Ramtekkar et al., 2010). Females with ADHD have fewer hyperactive/impulsive symptoms, more inattentive symptoms, present more commonly with the predominantly inattentive subtype and tend to be underdiagnosed when compared to boys with ADHD (Gaub and Carlson, 1997; Gershon, 2002; Hinshaw et al., 2006). Higher rates of anxiety, as well as lower rates of physical aggression and externalizing behaviors have also been found in girls when compared to boys with ADHD (Levy et al., 2005; Rucklidge, 2010; Skogli et al., 2013). Multiple structural magnetic resonance imaging (sMRI) studies have examined the structural src inhibitors correlates of childhood ADHD, but most of these studies included primarily or exclusively male participants. Early region-of interest (ROI) sMRI studies conducted in primarily male samples have revealed multiple regional grey matter (GM) volume abnormalities in children with ADHD, with the most consistent findings located in the prefrontal cortex, the right caudate and the cerebellum (Valera et al., 2007). More recent sMRI studies have relied on voxel-based morphometry (VBM), a whole brain, fully automated technique for characterizing regional brain volume on a voxel-wise basis (Good et al., 2001). In a meta-analysis encompassing seven pediatric VBM studies, as well as previous ROI studies examining the caudate nuclei volumes, children with ADHD presented with reduced right globus pallidus, caudate and putamen volumes when compared with typically developing children (Frodl and Skokauskas, 2012). The generalizability of these sMRI findings to girls with ADHD remains to be established. Only one VBM study to date included a sufficient number of boys and girls to examine gender effects in ADHD (Yang et al., 2008). Authors reported no interaction between diagnosis and gender, but several potential confounding factors were present: the study sample was characterized by a large age range (7–17 years), participants presented with various comorbidities, and most patients were receiving medication treatment. Three previous ROI structural studies also examined gender-by-diagnosis interactions in childhood ADHD (Mahone et al., 2011; Qiu et al., 2009; Dirlikov et al., 2014). Two of these studies were restricted to the frontal lobe, manually or automatically delimiting functionally relevant sub regions such as the primary motor cortex, the anterior cingulate cortex, the premotor region, the orbitofrontal cortex or the inferior prefrontal cortex (Mahone et al., 2011; Dirlikov et al., 2014). Mahone et al. (2011) reported significantly smaller left lateral premotor cortices in girls (but not boys) with ADHD when compared with TD participants (Mahone et al., 2011). Dirlikov et al. (2014) found widely distributed reductions of surface area in girls with ADHD in the bilateral dorsolateral prefrontal cortex, the left inferior lateral prefrontal cortex, the right medial prefrontal cortex and the right orbitofrontal cortex, while boys with ADHD showed reduced surface area in the right anterior cingulate cortex and in the left medial prefrontal cortex, when compared with TD children (Dirlikov et al., 2014). The third study examined the volumes of the caudate, putamen and globus pallidus, and reported significantly smaller basal ganglia volumes in boys with ADHD when compared with TD boys. No volume differences were reported in girls with ADHD when compared with TD girls (Qiu et al., 2009). Finally, in one previous study restricted to female participants, Castellanos et al. (2001) found no significant differences between girls with ADHD and TD girls when measuring the volumes of the caudate nucleus, globus pallidus, frontal lobe (total volume)) and cerebellum, while girls with ADHD exhibited decreased grey matter volumes of the posterior inferior lobule in the cerebellar vermis when compared to TD girls (Castellanos et al., 2001). This limited number of studies suggest that girls with ADHD may not exhibit the structural abnormalities of the basal ganglia consistently reported in predominantly male ADHD samples (Valera et al., 2007; Nakao et al., 2011; Frodl and Skokauskas, 2012).