Acknowledgements: This research was funded by the Wellcome Trust (Grant 104631/Z/14/Z to T.W.R.). A pilot study was funded by the NIHR Cambridge Biomedical Research Centre (BRC-1215-20014 to P.B.). For the purpose of open access, the author has applied a CC BY public copyright licence to any Author Accepted Manuscript version arising from this submission. This work was further supported by MHRUK and Angharad-Dodds Bursaries to M.B.; a Sir Henry Wellcome Trust Postdoctoral Research Fellowship (Grant 204727/Z/16/Z) to P.B.; Medical Research Council [MR N013433-1] and the Vice Chancellor's Awards to M.P.H.; Wellcome Trust Senior Investigator Award to T.W.R. supporting E.K. as a research assistant; CAPES, Angharad-Dodds and Grindley funds to A.M.F.L.P.S.; and an Alexander von Humboldt Fellowship for senior researchers (GBR 1202805 HFST-E) to K.D.E. The magnet and support staff were also funded by the NIHR Cambridge Biomedical Research Centre. The views expressed are those of the author(s) and not necessarily those of the NHS, the NIHR or the Department of Health and Social Care. The Cambridge 7T MRI facility is co-funded by the University of Cambridge and the Medical Research Council (MR/M008983/1). C.T.R. was funded by a Sir Henry Dale Fellowship from the Wellcome Trust and the Royal Society [098436/Z/12/B]. We thank all participants for their contributions to this study. We would also like to acknowledge all our collaborators for their contributions to our research, particularly Professor Angela C Roberts, Professor Edward T Bullmore, Alexander G. Murley, Polytimi Frangou, Uzay Emir, Dinesh Deelchand and the staff at Wolfson Brain Imaging Centre for their help and support.