Impaired consolidation of visuomotor adaptation in patients with multiple sclerosis.

BACKGROUND: Apart from inflammation and neurodegeneration, the individual clinical course of multiple sclerosis (MS) might be determined by differential adaptive capacities of the central nervous system. It has been postulated that the retention of adaptive training effects may be impaired in persons with MS (PwMS). OBJECTIVE: To investigate motor adaptation and consolidation capacities of people with MS in a visual motor adaptation task (VAT). METHODS: A total of 23 PwMS (Expanded Disability Status Scale (EDSS) score < 6) and 20 matched healthy controls were recruited. All participants completed three sessions of a VAT where a clockwise rotation angle of 30° was introduced as perturbation during the active learning part of the paradigm. The training session (T0 ) was repeated after 24 h (T1 ) and 72 h (T2 ). Directional errors and parameters of adaptation and retention were evaluated. RESULTS: PwMS showed similar adaptation and online learning abilities as controls. However, the retention ratio was significantly lower in patients compared to controls at T1 (p = 0.036) and T2 (p = 0.039). There was no significant correlation between the overall adaptation or retention ratio and the EDSS score, respectively. CONCLUSION: Our findings indicate intact adaptation, but limited consolidation, in patients with mild-to-moderate MS. Future studies are needed to define the neurobiological substrates of this plasticity and the extent to which it can influence clinical outcomes.

A Single Session of Anodal Cerebellar Transcranial Direct Current Stimulation Does Not Induce Facilitation of Locomotor Consolidation in Patients With Multiple Sclerosis.

Background: Multiple sclerosis (MS) may cause variable functional impairment. The discrepancy between functional impairment and brain imaging findings in patients with MS (PwMS) might be attributed to differential adaptive and consolidation capacities. Modulating those abilities could contribute to a favorable clinical course of the disease. Objectives: We examined the effect of cerebellar transcranial direct current stimulation (c-tDCS) on locomotor adaptation and consolidation in PwMS using a split-belt treadmill (SBT) paradigm. Methods: 40 PwMS and 30 matched healthy controls performed a locomotor adaptation task on a SBT. First, we assessed locomotor adaptation in PwMS. In a second investigation, this training was followed by cerebellar anodal tDCS applied immediately after the task ipsilateral to the fast leg (T0). The SBT paradigm was repeated 24 h (T1) and 78 h (T2) post-stimulation to evaluate consolidation. Results: The gait dynamics and adaptation on the SBT were comparable between PwMS and controls. We found no effects of offline cerebellar anodal tDCS on locomotor adaptation and consolidation. Participants who received the active stimulation showed the same retention index than sham-stimulated subjects at T1 (p = 0.33) and T2 (p = 0.46). Conclusion: Locomotor adaptation is preserved in people with mild-to-moderate MS. However, cerebellar anodal tDCS applied immediately post-training does not further enhance this ability. Future studies should define the neurobiological substrates of maintained plasticity in PwMS and how these substrates can be manipulated to improve compensation. Systematic assessments of methodological variables for cerebellar tDCS are urgently needed to increase the consistency and replicability of the results across experiments in various settings.