den Braber, Anouk [1] ; van ‘t Ent, Dennis [1] ; Stoffers, Diederick [2] ; Linkenkaer-Hansen, Klaus [3] ; I. Boomsma, Dorret [1] ; J.C. de Geus, Eco [1] [1] Department of Biological Psychology, VU University Amsterdam, The Netherlands. [2] Department of Sleep and Cognition, Netherlands Institute for Neuroscience, Amsterdam, The Netherlands. [3] Department of Integrative Neurophysiology, Center for Neurogenomics and Cognitive Research, Neuroscience Campus Amsterdam, VU University, The Netherlands.