Attribution 3.0 United States

This is an open access article, originally published at https://doi.org/10.1186/s10194-018-0896-5
Med mindre annet er angitt, så er denne innførselen lisensiert som Attribution 3.0 United States This is an open access article, originally published at https://doi.org/10.1186/s10194-018-0896-5