This article has been retracted at the request of the Editors: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). REASON: Key results are based on invalid data, according to a recent notification by the authors. The findings of the article are significantly related to dopamine D2 receptor occupancy data, obtained from a Positron Emission Tomography (PET) scan in five individuals. According to new evidence, PET data of two out of these individuals did not show a reliable signal at all, while the PET results of the remaining three subjects are partly invalid. As a result, the reported findings are most likely incorrect. The Journal of Psychiatric Research is dedicated to the highest scientific standards, therefore, this article has been retracted. The Editors regret if any misleading conclusions have been drawn from this publication, and apologies are offered to the readers of the journal.