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    • On the other hand larger

    2018-11-07

    On the other hand, larger volumes in the right ACC have been linked to harm avoidance, a temperamental disposition characterized by excessive worrying, pessimism and shyness, in both genders (Pujol et al., 2002). Women, who are known to be at higher risk for internalizing disorders (McLean et al., 2011), tend to exhibit larger volumes in the right ACC compared to men (Mann et al., 2011; Ruigrok et al., 2014). They also recruit more the right ventral ACC during emotional processing (Wrase et al., 2003); a finding confirmed in a quantitative meta-analysis of 65 neuroimaging studies of emotional processing (Wager et al., 2003). Based on these findings, it could be hypothesized that increased GM volumes in the right ventral ACC in girls with ADHD represent a risk factor for developing internalizing symptoms (Skogli et al., 2013). However, one must also note that reduced grey matter volumes in the ventral ACC have been consistently reported in patients suffering from internalizing disorders such as major depressive disorder or anxiety disorders, in both genders (Drevets et al., 2008; Van Tol et al., 2010). More studies in healthy children and adults are therefore needed to disentangle the relationships between grey matter volumes in the ventral ACC, pathological anxiety and temperamental anxiety. It may be that increased vs. decreased GM volumes in the ventral ACC represent both risk factors for anxiety symptoms, through different pathways (subtending, for example, a tendency to overthink vs. a lack of conscious integration of negative feelings (Bassett et al., 2015)); or that decreased GM volumes in the ventral ACC only appear in adult patients following a long-term history of depression or anxiety disorder, which would be consistent with the rna helicase neurotoxicity hypothesis (Treadway et al., 2009). Contrary to our hypotheses, we did not report decreased GM volumes in boys with ADHD when compared with TD boys in the basal ganglia. ADHD is a heterogeneous condition, involving multiple causal pathways (Sonuga-Barke and Halperin, 2010). Notably, findings from individual sMRI studies have been inconsistent, probably reflecting the neuropsychological and etiological heterogeneity of the disorder itself (Castellanos et al., 2006). Reduced GM volume in children with ADHD in the basal ganglia are one of the most replicated findings in sMRI studies (Nakao et al., 2011; Frodl and Skokauskas, 2012), but structural deficits in this region are not expected to be found in all subgroups of children with ADHD. Here, the lack of significant finding in the basal ganglia may also be related to the characteristics of our ADHD sample, which included boys with no psychiatric comorbidity, no learning disorder and a mean IQ of 105.7. Indeed, high-functioning samples presumably exhibit more subtle brain alterations that may be difficult to detect at a corrected statistical thresholding (Seidman et al., 2011). Similarly, we did not replicate previous findings from ROI structural studies reporting increased GM volumes in the left lateral premotor cortex, as well as decreased GM volumes in the posterior inferior lobule of the cerebellar vermis in girls with ADHD when compared to TD girls. Comparison between ROI and VBM findings can prove to be difficult. Indeed, ROI methods yield a single value for the volume of the region examined, obtained after averaging signal over the ROI. This signal averaging can cause a dilution of the measure of the volume difference, especially when this difference is only present in a limited part of the ROI (Voormolen et al., 2010). For this reason, VBM has been shown to outperform ROI methods when detecting focal differences in morphology (Voormolen et al., 2010). However, theoretically, ROI methods remain superior when between-group differences are distributed uniformly over a small ROI, since the ROI analysis at this spatial scale benefits from substantial signal averaging (Voormolen et al., 2010). Both methods can therefore provide different types of information and are considered as complementary (Giuliani et al., 2005).