Compromised tDCS-induced facilitation of motor consolidation in patients with multiple sclerosis

To investigate whether consolidation after motor learning can be facilitated by offline (post-training) transcranial direct current stimulation (tDCS) in patients with multiple sclerosis (MS). In this cross-sectional double-blind interventional study, effects of tDCS on motor consolidation were examined in 14 patients with relapsing remitting MS [median Expanded Disability Status Scale score 2.0 (range 1-4)] and 14 age- and sex-matched healthy controls. tDCS with the anode placed over the left primary motor cortex and the cathode placed over the right supraorbital region was applied immediately after a training session of an explicit sequential finger-tapping task that was performed with the right (dominant) hand. Task performance was retested after an interval of 8 h to assess consolidation. Participants took part in two experimental sessions separated by at least 7 days which differed with respect to type of post-training tDCS, i.e., sham and verum stimulation. Patients with MS performed worse than controls in functional motor tests and the motor sequence task. However, learning speed and magnitude of online performance increments during the training session were comparable to controls. While post-training tDCS facilitated motor consolidation in controls, patients with MS did not benefit from this type of intervention. Absence of post-training tDCS-induced facilitation of consolidation in patients with MS suggests that the interaction of tDCS with the motor consolidation network is inefficient. Identification of the underlying disease-related mechanisms will have important implications for the design of studies aiming to promote motor recovery in MS by non-invasive brain stimulation.