In the funding statement one source of funding was missing. This is now rectified as follows:
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
The authors would like to thank Dr. Tracy K. McIntosh for carefully editing the manuscript. Financial support was provided by the Italian Ministry of Health, Young Investigators Award 2009 (GR-2008-1136044) and by Fondazione Cariplo (grant number 2012-0590). FO was funded by a fellowship in memory of Amalia Ghezzi.