Cognitive Improvement Through tDCS for Patients With Multiple Sclerosis

Multiple sclerosis (MS) is a chronic inflammatory autoimmune disease characterized by a multitude of symptoms, which greatly reduce the quality of life of patients. In addition to sensory and visual sensory disorders, movement disorders, paresis, fatigue and other physical symptoms, 65-95% of patients with MS also suffer from cognitive impairments. These cognitive impairments develop in the later course of the disease and express themselves in slower processing speed, delays in learning and memory performance, and executive dysfunction. In recent years, non-pharmacological approaches aimed at improving cognitive performance in MS have increasingly come into focus, including the transcranial direct current stimulation (tDCS). TDCS has only been investigated in a few studies that had the aim to improve cognitive performance in MS. Further, it has only been carried out in combination with cognitive training paradigms and repeated stimulation sessions. Mattioli and colleagues (2016) could e.g. show that after 10 sessions of cognitive training with tDCS stimulation of the dorsolateral prefrontal cortex, there was greater improvement in symbol-digit modalities test (SDMT) in the experimental group than in the control group. Similarly, Charvet and colleagues (2018) showed that after 10 sessions of cognitive training with simultaneous tDCS stimulation of the dorsolateral prefrontal cortex, the experimental group showed a significant improvement in the domains of attention and response variability compared to the control group. These studies therefore reflect an interaction between cognitive training and tDCS, and do not allow any conclusions to be drawn about the effect of tDCS on specific processes. It is not yet known whether tDCS alone can positively influence specific cognitive functional impairments. Therefore, the present study wants to investigate whether acute application of tDCS can improve specific cognitive functions. An adapted version of the clinically SDMT was conducted, as this test is one of the most widely used tests to describe cognitive impairments in MS. Based on a meta-analysis by Silva and colleagues (2018), that shows which brain areas are related to the implementation of the SDMT, the parietal cortex (BA7) is stimulated bilaterally with either excitatory (anodal) or inhibitory (cathodal) tDCS.