1. a Department of Integrative Medical Biology, Section of Physiology , Umeå University , Umeå, 901 87, Sweden E-mail:
2. b Department of Biokinesiology & Physical Therapy , University of Southern California , 1540 East Alcazar Street, CHP 155, Los Angeles, California, 90089–9006
3. c Institute of Neuroscience and Physiology, Department of Physiology , Göteborg University , Göteborg, 405 30, Sweden