Comparison of CBF between healthy volunteers and MS patients:
\- Arterial spin labelling (ASL) is used to investigate cerebral blood flow in patients with MS and healthy volunteers.
The effect of transcranial direct current stimulation (tDCS) on cerebral blood flow:
* ASL scans are performed before-, during-, and after tDCS
* Each subject will receive active and sham tDCS (seperated by at least two days) (cross-over design).
Follow-up visit:
* After two years, patients with MS are re-invited.
* This visit will include a new neuropsychological evaluation, blood sampling and additional brain scans.
