1 Stroke Research Centre, UCL Queen Square Institute of Neurology, First Floor, Russell Square House, 10-12 Russell Square, London, WC1B 5EH, UK. philip.nash@ucl.ac.uk.
2 The National Hospital for Neurology and Neurosurgery, Queen Square, London, UK. philip.nash@ucl.ac.uk.
3 Stroke Research Centre, UCL Queen Square Institute of Neurology, First Floor, Russell Square House, 10-12 Russell Square, London, WC1B 5EH, UK.
4 The National Hospital for Neurology and Neurosurgery, Queen Square, London, UK.