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Tomasi D, Volkow ND.Tomasi D, et al.Proc Natl Acad Sci U S A. 2010 May 25;107(21):9885-90. doi: 10.1073/pnas.1001414107. Epub 2010 May 10.Proc Natl Acad Sci U S A. 2010.PMID: 20457896Free PMC article.