Conflict of interest statement
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
Acknowledgments
This work was supported by the Swiss National Science Foundation (31003A_135631, grant to AH), the National Centre of Competence in Research (NCCR) SYNAPSY financed by the Swiss National Science Foundation (51AU40_125759), the International Foundation for Research on Paraplegia, and the Hans Wilsdorf Foundation.