aChair of Neurophysiology, Center of Biomedicine and Medical Technology Mannheim, Medical Faculty Mannheim, University of Heidelberg, Mannheim 68167, Germany
bDepartment of Neurology, Philipps-University, Marburg, Germany
cSomnomar, Institute for Medical Research and Sleep Medicine, Marburg, Germany
* Tel.: +49 621 383 5070.
Received September 26, 2013
Accepted September 29, 2013