Global organization of functional brain connectivity in methamphetamine abusers Mehran Ahmadlou a,b,⇑ , Khodabakhsh Ahmadi c , Majid Rezazade d , Esfandiar Azad-Marzabadi c a Netherlands Institute for Neuroscience, Amsterdam, The Netherlands b Dynamic Brain Research Institute, Tehran, Iran c Behavioral Sciences Research Center, Baqiyatallah University of Medical Sciences, Tehran, Iran d Aids Prevention & Control Committee of Welfare Organization State, Tehran, Iran article info Article history: Accepted 7 December 2012 Available online xxxx Keywords: Coherence EEG Functional connectivity Methamphetamine Small-World Network Visibility graph similarity highlights  This is the first study on the effects of methamphetamine on the global organization of functional brain connectivity.  The normal Small-World brain network is disrupted at the gamma band in chronic methamphetamine abusers.  The global network deficit at gamma in methamphetamine abusers may imply on effects of the dis- rupted dopaminergic system on fast-spiking interneurons. abstract Objective: This study aimed to determine effects of chronic methamphetamine (MA) abuse on global organization of the functional brain connectivity. Methods: Eyes-closed resting-state EEGs of 36 MA abusers and 36 age-matched healthy subjects were recorded using a 32-channel system. The EEGs (1–60 Hz), after removing artifacts, were decomposed into the conventional EEG bands. Using visibility graph similarity (VGS) and coherence methods, the VGS and coherence matrices in each EEG band were constructed. Then the Small-World Network properties, clus- tering coefficient (C), mean path length (L) and C/L, of the VGS and coherence matrices, were computed in all EEG bands. Then using the Mann–Whitney test and an artificial neural network the differences of C, L and C/L between the two groups were evaluated. Results: The MA abusers showed higher C, lower L and higher C/L at the gamma band (p-value <0.005). An accuracy of 82.8% in discriminating the two groups was obtained by the classifier. Conclusions: The topology of the functional brain connectivity is disrupted in MA abusers, as depicted by deviation from Small-Worldness in the gamma band. Significance: This is the first but quasi-experimental study showing disrupted topology of the functional brain networks in MA abusers. Ó 2012 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved. 1. Introduction Methamphetamine (MA) is a highly addictive neuro-toxic and psycho-stimulant drug affecting the brain structurally and func- tionally (Belcher et al., 2009; Tobias et al., 2010; Iudicello et al., 2012). Compared with other addictive stimulants, MA is relatively inexpensive and easily synthesised (Newton et al., 2003; Kalech- stein et al., 2009), with substantially high risk of psychotic disor- ders (for the MA abusers) and a significant impact on public health (Glasner-Edwards et al., 2008; Henry et al., 2010). Also compared to opiate dependence, MA dependence causes greater impairment of cognitive functions (Feil et al., 2010). Moreover, the prevalence of MA use and abuse has increased over the past two decades (Polesskaya et al., 2011; Maxwell and Brecht, 2011). However, only a relatively small number of studies have investi- gated the effects of MA on the human brain (Feil et al., 2010). Decreased cerebral blood flow (Polesskaya et al., 2011), in- creased severity of white matter hyper-intensity signals (Bae et al., 2006), decreased grey matter density in bilateral insula and left middle frontal gyrus (Schwartz et al., 2010), reduced hippo- campal volume (Thompson et al., 2004) and abnormalities in regio- nal glucose metabolism (Belcher et al., 2009) are the main MA abuse effects on the human brain observed in imaging studies. The effects of the MA abuse on brain electrical activity have been reported also in some, but few, studies. 1388-2457/$36.00 Ó 2012 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved. http://dx.doi.org/10.1016/j.clinph.2012.12.003 ⇑ Corresponding author at: Netherlands Institute for Neuroscience, Amsterdam, The Netherlands. Tel.: +31 613750152; fax: +98 2188790869. E-mail addresses: m.ahmadlou@nin.knaw.nl, mehranahmadlou@gmail.com (M. Ahmadlou). Clinical Neurophysiology xxx (2013) xxx–xxx Contents lists available at SciVerse ScienceDirect Clinical Neurophysiology journal homepage: www.elsevier.com/locate/clinph Please cite this article in press as: Ahmadlou M et al. Global organization of functional brain connectivity in methamphetamine abusers. Clin Neurophysiol (2013), http://dx.doi.org/10.1016/j.clinph.2012.12.003