Resumen de Cognitive and motor neurobehavioral relationships in people with multiple sclerosis and healthy individuals
Even though cognition and motor behavior have been traditionally conceived as independent processes, a growing body of literature supports that motor and cognitive processes are highly interrelated (Hommel et al., 2016; Mirelman et al., 2018). The relative contribution of cognition -or executive control- to motor behavior has been evidenced by means of a behavioral approach (e.g. dual task) and/or a neurophysiological approach (Clark, 2015). In this context, a deeper understanding of the cognitive-motor interference that arises from the dual task performance of a motor and cognitive task is needed, as well as the characterization of cognitive demand in neural oscillatory activity in motor-related cortical regions of the brain. The general aim of this thesis is to examine the interplay between cognitive and motor processes by means of its effect on behavior and neural correlates in people with Multiple Sclerosis and healthy individuals. It will be achieved through the study of the cognitive-motor interference during dual-task performance in people with Multiple Sclerosis and healthy individuals, as well as through the study of oscillatory brain activity potentially associated with the cognitive demand during motor control in a healthy sample. The focus is not only theoretical but also applied since the cognitive-motor interference is evaluated for its applicability to the cognitive functional assessment of people with Multiple Sclerosis. The first study consisted of a mixed methods systematic review about cognitive-motor interference during gait in people with Multiple Sclerosis and healthy individuals. The mixed-methods approach allowed a comprehensive and detailed review of the highly heterogeneous literature in terms of procedures, and the identification of variables that might account for the differences between studies. It showed that people with Multiple Sclerosis had significant cognitive-motor interference, and that the use of the Verbal Fluency task while walking and the measurement of the gait parameter of double support time were sensitive and specific to cognitive-motor interference in people with Multiple Sclerosis; thus, providing a rationale for the use of the cognitive-motor interference paradigm with this procedure for the assessment of people with Multiple Sclerosis. The need to assess cognitive-motor interference over cognitive performance, give standardized instructions and evaluate between-group (people with Multiple Sclerosis versus healthy controls) as well as intragroup changes was emphasized. The second study examined cognitive-motor interference under different instructions of prioritization and explored its association with other neuropsychological, symptomatic, physiological and clinical variables in people with Relapsing-Remitting Multiple Sclerosis and healthy controls. Results revealed significant cognitive-motor interference over cognitive performance in people with Multiple Sclerosis, but not in healthy controls. The instructions of dual-task prioritization had an effect over motor and cognitive performance. Furthermore, cognitive-motor interference was associated with neuropsychological, symptomatic and psychophysiological variables (P3 component of the event-related potentials) suggesting that it might be a potential marker of cognitive decline in people with Multiple Sclerosis. The third study involved an electroencephalography recording of healthy young adults for the examination of oscillatory beta activity (~13-35 Hz) in supplementary and primary motor cortical regions with respect to cognitive demand during the performance of a center-out visuomotor task. The task consisted on navigating on a digitizing tablet to reach a target shown on the screen with a pen under a normal unperturbed (automatic) condition and an anti-movement (controlled) condition with inverted axes representation. Results revealed significantly greater power in beta oscillations (or less beta desynchronization) in the supplementary motor area during motor preparation in controlled compared to the automatic condition, which was associated with improved motor performance (i.e. less trajectory error to reach the target). The results demonstrate an association of beta oscillations in the supplementary motor area with cognitive control during motor preparation. The findings shed light on cortical oscillatory mechanisms of inhibition and corroborate a role for medial frontal cortex for cautious control in movement execution. Overall, the findings of this thesis add to the evidence supporting the link between cognitive and motor processes.
