1 Department of Old Age Psychiatry, Institute of Psychiatry, Psychology and Neuroscience, King's College London, London, UK. dag.aarsland@kcl.ac.uk.
2 Centre for Age-Related Medicine, Stavanger University Hospital, Stavanger, Norway. dag.aarsland@kcl.ac.uk.
3 Parkinson's Foundation Centre of Excellence, King's College Hospital and Institute of Psychiatry, Psychology and Neuroscience, King's College London, London, UK.
4 Brain and Mind Centre and Faculty of Medicine and Health School of Medical Sciences, University of Sydney, Sydney, New South Wales, Australia.
5 Amsterdam UMC, University of Amsterdam, Department of Medical Psychology, Amsterdam Neuroscience, Amsterdam, The Netherlands.
6 University of Exeter Medical School, Exeter, UK.
7 Departments of Psychiatry and Neurology, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA.
8 Parkinson's Disease Research, Education and Clinical Center (PADRECC), Corporal Michael J. Crescenz Veterans Affairs Medical Center, Philadelphia, PA, USA.