Acknowledgements

This work was supported by an MRC Programme Grant (to BJE, TWR, and Anthony Dickinson) and a Wellcome Trust programme grant (to TWR, BJE, Angela C. Roberts, and Barbara J Sahakian), and was conducted within the MRC Co-operative for Brain, Behaviour and Neuropsychiatry. RNC was supported by the UK Medical Research Council and the University of Cambridge School of Clinical Medicine. JH was supported by Trinity College, Cambridge and the University of Cambridge School of Clinical Medicine.