Amphetamine-type stimulants (ATS) refer to a group of drugs whose principal members include amphetamine, methamphetamine and 3,4-methylenedioxymethamphetamine (MDMA). Worldwide, ATS are among the most common illicit drugs. Therefore, understanding whether and to what extent ATS exposure affects brain structure and functioning in recreational users has become a critical public health issue. We studied gray and white matter densities in 20 experienced users of ATS (more than 100 units MDMA and/or 50 g of amphetamine lifetime dose), 42 low exposure users with very limited ATS experience (less than 5 units lifetime dose) and 16 drug-naive controls. A tract-based spatial statistics (TBSS) analysis of fractional anisotropy images was applied to diffusion magnetic resonance imaging (MRI) data. Furthermore, alignment invariant white matter tract representations acquired from the TBSS analysis were used as a reference for inter-subject brain registrations in a voxel-based morphometry (VBM) analysis of gray matter volume, reducing characteristic alignment inaccuracies associated with this voxel-wise gray matter investigation approach. Between-group white matter comparison revealed no significant results. However, compared to low exposure users, experienced users showed several regions of lower gray matter volume in medial frontal regions, in particular the orbital and medial frontal cortex. Differences are likely to reflect effects of repeated ATS exposure even in recreational users. However, differences in pre-existing or confounding factors might also account for between-group differences.
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